PHOTOELECTRIC CONVERSION ELEMENT AND IMAGING DEVICE

A photoelectric conversion element 10A according to an embodiment of the present disclosure includes: a first electrode 21; a second electrode 23 that is disposed to be opposed to the first electrode 21; and a photoelectric conversion layer 22 that is provided between the first electrode 21 and the second electrode 23. The photoelectric conversion layer 22 includes a hole transporting material as a first organic semiconductor material. The hole transporting material absorbs blue light.

TECHNICAL FIELD

The present disclosure relates to a photoelectric conversion element in which, for example, an organic material is used and an imaging device including the photoelectric conversion element.

BACKGROUND ART

For example, PTL 1 discloses a photoelectric conversion element in which a photoelectric conversion layer is formed by using three types of materials. In this photoelectric conversion element, an organic semiconductor material that has the maximum absorption in a predetermined wavelength range is used as one of the three types of materials and organic semiconductor materials each having high transparency in the visible light region are used as the two other materials. This allows the photoelectric conversion element to achieve high photoelectric conversion efficiency for the predetermined wavelength range.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Incidentally, an imaging device has been required to have an extended absorption spectrum.

It is desirable to provide a photoelectric conversion element and an imaging device each having a wide absorption spectrum.

A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode; a second electrode that is disposed to be opposed to the first electrode; and a photoelectric conversion layer that is provided between the first electrode and the second electrode. The photoelectric conversion layer includes a hole transporting material as a first organic semiconductor material. The hole transporting material absorbs blue light.

An imaging device according to an embodiment of the present disclosure includes the one or more photoelectric conversion elements according to the embodiment of the present disclosure described above for each of a plurality of pixels.

In the photoelectric conversion element according to the embodiment of the present disclosure and the imaging device according to the embodiment, the hole transporting material that absorbs the blue light is used for the photoelectric conversion layer as the first organic semiconductor material, thereby extending the absorption spectrum of the photoelectric conversion layer.

MODES FOR CARRYING OUT THE INVENTION

The following describes an embodiment of the present disclosure in detail with reference to the drawings. The following description is a specific example of the present disclosure, but the present disclosure is not limited to the following modes. In addition, the present disclosure is not also limited to the disposition, dimensions, dimension ratios, and the like of the respective components illustrated in the respective diagrams. It is to be noted that description is given in the following order.

1. Embodiment (an example of a photoelectric conversion element including an organic photoelectric conversion layer including a hole transporting material that absorbs blue light)

1-1. Configuration of Photoelectric Conversion Element

1-2. Configuration of Imaging Device

1-3. Workings and Effects

2. Modification Examples

2-1. Modification Example 1 (an example in which a spectrum adjustment layer is added)
2-2. Modification Example 2 (an example in which an organic photoelectric conversion section that detects blue light and an inorganic photoelectric conversion section that detects red light and green light are stacked)
2-3. Modification Example 3 (an example in which organic photoelectric conversion layers each having different spectral characteristics are stacked)

3. Application Examples

4. Practical Application Examples

5. Working Examples

FIG.1illustrates an example of a cross-sectional configuration of a photoelectric conversion element (photoelectric conversion element10A) according to an embodiment of the present disclosure.FIG.2illustrates an example of an overall configuration of an imaging device (imaging device1) including the photoelectric conversion element10A illustrated inFIG.1. The photoelectric conversion element10A is included, for example, in one pixel (unit pixel P) in the imaging device1such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor used, for example, for an electronic apparatus such as a digital still camera or a video camera. The photoelectric conversion element10A according to the present embodiment includes an organic photoelectric conversion section20. An organic photoelectric conversion layer22included in this organic photoelectric conversion section20is formed by using a hole transporting material that absorbs blue light.

1-1. Configuration of Photoelectric Conversion Element

The photoelectric conversion element10A includes, for example, the one organic photoelectric conversion section20. The organic photoelectric conversion section20includes the organic photoelectric conversion layer22between a lower electrode21(first electrode) and an upper electrode23(second electrode) that are disposed to be opposed to each other. The organic photoelectric conversion layer22is formed by using the organic semiconductor material described above as an organic material. The organic photoelectric conversion section20detects a portion or the whole of the wavelength of the visible light region (e.g., 400 nm or more and 760 nm or less).

In the present embodiment, there are provided color filters51(color filters51R.51G, and51B) above the organic photoelectric conversion section20(light incidence side) for the respective unit pixels P (unit pixels Pr, Pg, and Pb). The color filters51(color filters51R,51G, and51B) selectively transmit red light (R), green light (G), and blue light (B). This causes the organic photoelectric conversion section20to detect the red light passing through the color filter51R in the unit pixel Pr provided with the color filter51R and generate the signal charge corresponding to the red light (R). The organic photoelectric conversion section20detects the green light passing through the color filter51G in the unit pixel Pg provided with the color filter51G and generates the signal charge corresponding to the green light (G). The organic photoelectric conversion section20detects the blue light passing through the color filter51B in the unit pixel Pb provided with the color filter51B and generates the signal charge corresponding to the blue light (B).

The photoelectric conversion element10A further includes, for example, one inorganic photoelectric conversion section32. The inorganic photoelectric conversion section32is formed to be buried in a semiconductor substrate30. The inorganic photoelectric conversion section32detects light in a wavelength range different from that of the organic photoelectric conversion section20and performs photoelectric conversion. In other words, the organic photoelectric conversion section20and the inorganic photoelectric conversion section32each detect light in a different wavelength range and perform photoelectric conversion. Specifically, the organic photoelectric conversion section20detects the wavelength of the visible light region and the inorganic photoelectric conversion section32detects the wavelength of the infrared light region (e.g., 700 nm or more and 1000 nm or less).

The organic photoelectric conversion section20and the inorganic photoelectric conversion section32are stacked, for example, in the vertical direction. Specifically, the organic photoelectric conversion section20is disposed, for example, on a light incidence side S1 side and provided, for example, on a first surface30A (back surface) side of the semiconductor substrate30.

This causes the pieces (R, G, and B) of light in the visible light region among the pieces of light passing through the respective color filters51R,51G, and51B to be each absorbed by the organic photoelectric conversion section20. The other light passes through the organic photoelectric conversion section20. Specifically, light in the infrared light region passes through the organic photoelectric conversion section20. This light (that is referred to simply as infrared light (IR) below) in the infrared light region that has passed through the organic photoelectric conversion section20is detected by the inorganic photoelectric conversion section32of each of the unit pixels Pr, Pg, and Pb. Each of the unit pixels Pr, Pg, and Pb generates the signal charge corresponding to the infrared light (IR). In other words, the imaging device1including the photoelectric conversion element10A is able to concurrently generate both a visible light image and an infrared light image.

It is to be noted that, in the present embodiment, a case is described where the electron of a pair (electron-hole pair) of an electron and a hole generated by photoelectric conversion is read out as signal charge (case where an n-type semiconductor region is used as a photoelectric conversion layer). In addition, “+(plus)” attached to “n” indicates a high concentration of n-type impurities in a diagram.

A second surface30B (front surface) of the semiconductor substrate30is provided, for example, with an electric charge holding section33and a pixel transistor and a multilayer wiring layer40that are not illustrated. In the multilayer wiring layer40, for example, wiring layers41,42, and43are stacked in an insulating layer44.

It is to be noted that the diagram illustrates the back surface (first surface30A) side of the semiconductor substrate30as the light incidence side S1 and the front surface (second surface30B) side thereof as a wiring layer side S2.

The organic photoelectric conversion section20has a configuration in which the lower electrode21, the organic photoelectric conversion layer22, and the upper electrode23are stacked in this order from the first surface30A side of the semiconductor substrate30as described above. The lower electrodes21are separately formed, for example, for the respective photoelectric conversion elements10A.FIG.1illustrates an example in which the organic photoelectric conversion layer22and the upper electrode23are provided as continuous layers common between the respective unit pixels Pr, Pg, and Pb, but the organic photoelectric conversion layers22and the upper electrodes23may also be separately formed for the respective unit pixels Pr. Pg, and Pb as with the lower electrodes21.

There is provided, for example, an interlayer insulating layer34between the first surface30A of the semiconductor substrate30and the organic photoelectric conversion section20. For example, the color filter51is provided above the upper electrode23as described above. Although not illustrated, there are provided, for example, optical members such as a planarization layer and an on-chip lens above the color filter51.

There is provided, for example, a through electrode35between the first surface30A of the semiconductor substrate30and the second surface30B. The lower electrode21is electrically coupled to the electric charge holding section33through the through electrode35. In other words, the through electrode35has a function of a connector for the organic photoelectric conversion section20and the electric charge holding section33and also serves as a transmission path for the signal charge generated in the organic photoelectric conversion section20. This allows the photoelectric conversion element10A to favorably transfer the signal charge (electrons here) generated by the organic photoelectric conversion section20on the first surface30A side of the semiconductor substrate30to the second surface30B side of the semiconductor substrate30through the through electrode35and increase the characteristics. There is provided, for example, an insulating film36around the through electrode35. This electrically insulates the through electrode35and a p-well31.

In the organic photoelectric conversion section20according to the present embodiment, light coming from the upper electrode23side is absorbed by the organic photoelectric conversion layer22. The excitons generated by this move to the interface between an electron donor and an electron acceptor included in the organic photoelectric conversion layer22and undergo exciton separation. In other words, the excitons dissociate into electrons and holes. The electric charge (electrons and holes) generated here is transported to different electrodes by diffusion due to a carrier concentration difference and an internal electric field caused by a work function difference between the anode (upper electrode23here) and the cathode (lower electrode21here). The transported electric charge is detected as a photocurrent. In addition, the application of a potential between the lower electrode21and the upper electrode23makes it possible to control the transport directions of electrons and holes.

The following describes configurations, materials, and the like of the respective sections.

The organic photoelectric conversion section20is an organic photoelectric conversion element that absorbs the light corresponding to the wavelength range of a portion or the whole of the visible light region to generate an electron-hole pair.

The lower electrode21is for attracting, as signal charge, electrons of the electric charge generated in the organic photoelectric conversion layer22and transferring the attracted signal charge to the electric charge holding section33. The lower electrode21includes an electrically conducive film having light transmissivity. The lower electrode21includes, for example, ITO (indium tin oxide). However, a tin oxide (SnO2)-based material to which a dopant is added or a zinc oxide-based material obtained by adding a dopant to zinc oxide (ZnO) may be used in addition to this ITO as a material included in the lower electrode21. Examples of the zinc oxide-based material include aluminum zinc oxide (AZO) to which aluminum (Al) is added as a dopant, gallium zinc oxide (GZO) to which gallium (Ga) is added, and indium zinc oxide (IZO) to which indium (In) is added. In addition, CuI, InSbO4, ZnMgO, CuInO2, MgIN2O4, CdO, ZnSnO3, TiO2, or the like may be used as a material included in the lower electrode21. Further, spinel oxide or oxide having a YbFe2O4structure may be used.

The organic photoelectric conversion layer22converts light energy into electric energy. The organic photoelectric conversion layer22is formed to include, for example, two or more types of organic materials that each function as a p-type semiconductor or an n-type semiconductor. The organic photoelectric conversion layer22has a bulk heterojunction structure in the layer. The bulk heterojunction structure is a p/n junction surface that is formed by mixing the p-type semiconductor and the n-type semiconductor and excitons generated by absorbing light are separated into electrons and holes at the p/n junction interface. It is to be noted that the p-type semiconductor relatively functions as an electron donor (donor) and the n-type semiconductor relatively functions as an electron acceptor (acceptor). The organic photoelectric conversion layer22provides a field where excitons generated upon light absorption are separated into electrons and holes. Specifically, the excitons are separated into electrons and holes at the interface (p/n junction surface) between the electron donor and the electron acceptor.

The organic photoelectric conversion layer22may further include, in addition to the p-type semiconductor and the n-type semiconductor, three types of organic materials or so-called dye materials each of which photoelectrically converts light in a predetermined wavelength band while transmitting light in another wavelength band. It is preferable that the p-type semiconductor, the n-type semiconductor, and the dye materials each have a different absorption maximum wavelength. This makes it possible to widely absorb light in the visible light region.

In the present embodiment, a hole transporting material that absorbs blue light is used as one of two or three types of organic materials that form the organic photoelectric conversion layer22. This hole transporting material that absorbs blue light has an absorption maximum wavelength on the shortest wavelength side, for example, among the two or three types of organic materials that form the organic photoelectric conversion layer22. In addition, it is preferable that the hole transporting material which absorbs blue light have a shallower Highest Occupied Molecular Orbital (HOMO) level than the HOMO level of a second organic semiconductor material included in the organic photoelectric conversion layer22described below. Further, it is preferable that the hole transporting material which absorbs blue light have crystallizability and have a herringbone-type molecular arrangement, for example, in the layer of the organic photoelectric conversion layer22.

Examples of such a hole transporting material that absorbs blue light include a dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene derivative (that is referred to as DTBDT derivative below) represented by the following general formula (1) or general formula (2). The DTBDT derivative represented by this general formula (1) or general formula (2) correspond to specific examples of a “first organic semiconductor material” according to the present disclosure.

Specific substituents introduced into R1, R2, R3, and R4 include the following formula (A-1) to formula (A-53). A carbon atom bonded to A in any of the formulas forms a bond with a carbon atom bonded to any of R1, R2, R3, and R4 represented by the general formula (1) or the general formula (2).

As a specific example of the DTBDT derivative represented by the general formula (1) or the general formula (2) described above, for example, the compounds represented by the following formula (1-1) to formula (1-5) are included.

The organic photoelectric conversion layer22may further include an organic semiconductor material having an electron transporting property. This organic semiconductor material having an electron transporting property corresponds to a specific example of the “second organic semiconductor material” according to the present disclosure. Examples of the organic semiconductor material having an electron transporting property include the fullerene Cao represented by the following formula (3) or the fullerene C70represented by the formula (4), a derivative thereof, or the like.

It is possible to form the organic photoelectric conversion layer22by using further an organic material or a so-called dye material that photoelectrically converts light in a predetermined wavelength band of the visible light region and transmits pieces of light in the other wavelength bands as one of the two or three types of organic materials that form the organic photoelectric conversion layer22. This dye material corresponds to a specific example of a “third organic semiconductor material” according to the present disclosure.

Examples of the dye material include subphthalocyanine, dipyrromethene, merocyanine, or squarylium or a derivative thereof that absorbs light in a wavelength band of 500 nm or more and 600 nm or less. In addition, for example, any of naphthalene, anthracene, phenantherene, tetracene, pyrene, perylene, and fluoranthene or derivatives thereof may be used as the dye material. Alternatively, a polymer such as phenylenevinylene, fluorene, carbazole, indole, pyrene, pyrrole, picoline, thiophene, acetylene, or diacetylene or a derivative thereof may be used. Additionally, it is possible to favorably use a metal complex dye, a cyanine-based dye, a merocyanine-based dye, a phenylxanthene-based dye, a triphenylmethane-based dye, a rhodacyanine-based dye, a xanthene-based dye, a macrocyclic azaannulene-based dye, an azulene-based dye, naphthoquinone, an anthraquinone-based dye, a chain compound in which a fused polycyclic aromatic group such as anthracene and pyrene and an aromatic ring or a heterocyclic compound are fused, a cyanine-like dye bonded by two nitrogen-containing hetero rings such as quinoline, benzothiazole, and benzoxazole that have a squarylium group and a croconic methine group as a bonded chain or by a squarylium group and a croconic methine group, or the like. It is to be noted that a dithiol metal complex-based dye, a metallophthalocyanine dye, a metalloporphyrine dye, or a ruthenium complex dye is preferable as the metal complex dye described above, but this is not limitative.

In this way, the organic photoelectric conversion layer22is formed by using a plurality of organic semiconductor materials each having a different absorption maximum wavelength or a hole transporting material that absorbs blue light, a fullerene or a derivative thereof, and a so-called dye material in specific terms. This makes it possible to widely absorb light in the visible light region.

It is to be noted that the organic semiconductor materials described above function as a p-type semiconductor or an n-type semiconductor in accordance with a combination thereof.

For example, the variety of organic semiconductor materials described above are mixed and a vacuum evaporation method is used, thereby making it possible to form the organic photoelectric conversion layer22. In addition, for example, spin coating technology, printing technology, or the like may be used.

The upper electrode23includes an electrically conducive film having light transmissivity as with the lower electrode21.

There may be provided other layers between the organic photoelectric conversion layer22and the lower electrode21and between the organic photoelectric conversion layer22and the upper electrode23. Specifically, for example, an electron blocking film, the organic photoelectric conversion layer22, a hole blocking film, a work function adjustment layer, and the like may be stacked in order from the lower electrode21side. Further, there may be provided an underlying layer and a hole transport layer between the lower electrode21and the organic photoelectric conversion layer22and there may be provided a buffer layer and an electron transport layer between the organic photoelectric conversion layer22and the upper electrode23.

The semiconductor substrate30includes, for example, an n-type silicon (Si) substrate and includes the p-well31in a predetermined region.

The inorganic photoelectric conversion section32includes, for example, a PIN (Positive Intrinsic Negative) type photodiode PD and has a pn junction in a predetermined region of the semiconductor substrate30. The inorganic photoelectric conversion section32detects light (infrared light (IR)) in the wavelength range of a portion or the whole of the infrared light region. The second surface30B of the semiconductor substrate30is provided with pixel transistors including a transfer transistor, an amplification transistor, a reset transistor, and the like in addition to the electric charge holding section33.

The interlayer insulating layer34includes, for example, a single layer film including one of silicon oxide (SiOx), TEOS, silicon nitride (SiNx), silicon oxynitride (SiON), and the like or a stacked film including two or more of them.

It is possible to form the through electrode35by using, for example, metal materials such as aluminum (Al), tungsten (W), titanium (Ti), cobalt (Co), hafnium (H), and tantalum (Ta) in addition to a doped silicon material such as PDAS (Phosphorus Doped Amorphous Silicon).

The insulating film36is for electrically separating the semiconductor substrate30and the through electrode35. It is possible to form the insulating film36by using silicon oxide (SiOx), TEOS, silicon nitride (SiNx), silicon oxynitride (SiON), and the like as with the interlayer insulating layer34.

1-2. Configuration of Imaging Device

The imaging device1is, for example, a CMOS image sensor. The imaging device1takes in incident light (image light) from a subject through an optical lens system (not illustrated). The imaging device1converts the amount of incident light formed on the imaging surface as an image into electric signals in units of pixels and outputs the electric signals as pixel signals. The imaging device1includes a pixel section100serving as an imaging area on the semiconductor substrate30. The imaging device1includes, for example, a vertical drive circuit111, a column signal processing circuit112, a horizontal drive circuit113, an output circuit114, a control circuit115, and an input/output terminal116in a peripheral region of this pixel section100.

The pixel section100includes, for example, the plurality of unit pixels P that is two-dimensionally disposed in a matrix. These unit pixels Pare provided with a pixel drive line Lread (specifically, a row selection line and a reset control line) for each of the pixel rows and provided with a vertical signal line Lsig for each of the pixel columns. The pixel drive line Lread is for transmitting drive signals for reading out signals from the pixels. One end of the pixel drive line Lread is coupled to an output end corresponding to each of the rows of the vertical drive circuit111.

The vertical drive circuit11includes a shift register, an address decoder, and the like and is a pixel driver that drives the respective unit pixels P of the pixel section100, for example, in units of rows. The signals outputted from the respective unit pixels P in the pixel rows selectively scanned by the vertical drive circuit111are supplied to the column signal processing circuits112through the respective vertical signal lines Lsig. Each of the column signal processing circuits112includes an amplifier, a horizontal selection switch, and the like that are provided for each of the vertical signal lines Lsig.

The horizontal drive circuit113includes a shift register, an address decoder, and the like and drives the respective horizontal selection switches of the column signal processing circuits112in order while scanning the horizontal selection switches. This selective scanning by the horizontal drive circuit113outputs the signals of the respective pixels transmitted through the respective vertical signal lines Lsig to a horizontal signal line121in order and transmits the signals to the outside of the semiconductor substrate30through the horizontal signal line121.

The output circuit114performs signal processing on the signals sequentially supplied from the respective column signal processing circuits112through the horizontal signal line121and outputs the signals. The output circuit114performs, for example, only buffering in some cases and performs black level adjustment, column variation correction, various kinds of digital signal processing, and the like in other cases.

The circuit portions including the vertical drive circuit111, the column signal processing circuit112, the horizontal drive circuit113, the horizontal signal line121, and the output circuit114may be formed directly on the semiconductor substrate30or may be provided in external control IC. In addition, those circuit portions may be formed in another substrate coupled by a cable or the like.

The control circuit115receives a clock supplied from the outside of the semiconductor substrate30, data for an instruction about an operation mode, and the like and also outputs data such as internal information of the imaging device1. The control circuit115further includes a timing generator that generates a variety of timing signals and controls the driving of peripheral circuits such as the vertical drive circuit111, the column signal processing circuit112, and the horizontal drive circuit113on the basis of the variety of timing signals generated by the timing generator.

An input/output terminal16exchanges signals with the outside.

1-3. Workings and Effects

It is possible in the photoelectric conversion element10A according to the present embodiment and the imaging device1including the photoelectric conversion element10A to extend the absorption spectrum of the organic photoelectric conversion layer22by forming the organic photoelectric conversion layer22with a hole transporting material that absorbs blue light. The following describes this.

Image sensors in each of which an organic photoelectric conversion film is used have been developed for CCD (Charge Coupled Device) image sensors, CMOS image sensors, and the like. For example, an organic imaging device is proposed in which an organic photoelectric conversion film is used that has a multilayer structure in which an organic photoelectric conversion film having sensitivity to blue light (B), an organic photoelectric conversion film having sensitivity to green light (G), and an organic photoelectric conversion film having sensitivity to red light (R) are sequentially stacked. This image sensor achieves an increase in the sensitivity by extracting B/G/R signals separately from one pixel. In addition, an imaging device has been proposed in which an organic photoelectric conversion film formed by using the one type of organic semiconductor material that has the maximum absorption in a predetermined wavelength range and the two types of organic semiconductor materials that have high transparency in the visible light region as described above is stacked on a semiconductor substrate in which a photodiode is formed as an inorganic photoelectric conversion section. In this imaging device, a signal of one color is extracted by the organic photoelectric conversion film and signals of two colors are extracted by silicon (Si) bulk spectroscopy.

Incidentally, in recent years, image sensors have been requested to be developed that are each able to capture images obtained from both visible light and infrared light (IR). For example, in a case where the organic imaging device described above is applied, it is possible to absorb a wider visible light region, but an issue is raised with difficulty in manufacturing a commercial-size imaging device by the current technology.

Meanwhile, in a case where the above-described organic photoelectric conversion film including the three types of organic semiconductor materials stacked on a semiconductor substrate in which a photodiode is formed as an inorganic photoelectric conversion section is applied as the photoelectric conversion film of the above-described image sensor for visible light, this organic photoelectric conversion film raises an issue with the inability to offer sufficient sensitivity because the organic photoelectric conversion film is configured to selectively absorb a predetermined range of the visible light region.

In contrast, in the present embodiment, a hole transporting material that absorbs blue light is used as an organic material included in the organic photoelectric conversion layer22. This makes it possible to extend the absorption spectrum of the organic photoelectric conversion layer22.

For example, the organic photoelectric conversion layer22is formed by using this hole transporting material that absorbs blue light and one or two types of organic materials that each have an absorption maximum wavelength different from the absorption maximum wavelength of the hole transporting material. This increases light absorption for the blue region as compared with a case where the organic photoelectric conversion layer22is formed by using the one type of organic semiconductor material that has the maximum absorption in the predetermined wavelength range and the two types of organic semiconductor materials that have high transparency in the visible light region described above.

As described above, a hole transporting material that absorbs blue light is used as an organic material included in the organic photoelectric conversion layer22in the photoelectric conversion element10A according to the present embodiment. This makes it possible to extend the absorption spectrum of the organic photoelectric conversion layer22. This makes it possible to provide the photoelectric conversion element10A having a wide absorption spectrum and the imaging device1including the photoelectric conversion element10A.

In addition, in the present embodiment, it is possible to form an organic photoelectric conversion layer that detects the blue light (B) and the red light (R) and an organic photoelectric conversion layer that detects the blue light and the green light (G) by selecting, as appropriate, a dye material that is used along with the hole transporting material which absorbs blue light described above. This makes it possible to decrease, from three layers to two layers or one layer, the number of organic photoelectric conversion films that are stacked in the organic imaging device described above in which the three organic photoelectric conversion films are stacked. In other words, it is possible to manufacture the photoelectric conversion element10A widely having light absorption and the imaging device1including the photoelectric conversion element10A in simple steps.

Next, modification examples 1 to 3 of the present disclosure are described. The following assigns the same signs to components similar to those of the embodiment described above and omits descriptions thereof as appropriate.

2. Modification Examples

FIG.3illustrates an example of a cross-sectional configuration of a photoelectric conversion element (photoelectric conversion element10B) according to a modification example 1 of the present disclosure. The photoelectric conversion element10A described in the embodiment described above may be further provided, for example, a dual bandpass filter71as a spectrum adjustment layer.

The dual bandpass filter71has respective transmission bands for the visible light region and the infrared light region. The dual bandpass filter71is provided, for example, above the color filter51.

In a case where the color filters51R,51G, and51B and the organic photoelectric conversion section20are disposed above the first surface30A of the semiconductor substrate30serving as a light incidence surface as in the embodiment described above, the pieces of infrared light (IR) absorbed by the inorganic photoelectric conversion sections32of the respective unit pixels Pr, Pg, and Pb are the pieces of light that have passed through the respective color filters51R.51G, and51B and the organic photoelectric conversion section20. In other words, the pieces of infrared light (IR) absorbed by the inorganic photoelectric conversion sections32of the respective unit pixels Pr, Pg, and Pb each have a different spectrum. The respective unit pixels Pr, Pg, and Pb are thus different in sensitivity. This raises an issue with the unavailability of the respective unit pixels Pr, Pg, and Pb as IR pixels for generating the same infrared light image.

For this, in the present modification example, providing the dual bandpass filter71causes the pieces of infrared light (IR) detected by the inorganic photoelectric conversion sections32to be pieces of light in the wavelength region of the transmission band of the dual bandpass filter71on the infrared light region side. This allows the respective unit pixels Pr, Pg, and Pb to detect pieces of infrared light (IR) having uniform spectra. This allows the photoelectric conversion element10B to obtain an IR image in which IR signals are used that are obtained from all of the unit pixels Pr, Pg. and Pb arranged two-dimensionally. This makes it possible to provide the imaging device1that is able to obtain an IR image with high resolution in addition to the effects of the embodiment described above.

In addition, it is also possible to use a multilayer film filter81as a spectrum adjustment layer as in a photoelectric conversion element10C, for example, illustrated inFIG.4in addition to the dual bandpass filter71. In the multilayer film filter81, for example, films each including an inorganic material having a high refractive index and films each including an inorganic material having a low refractive index are periodically stacked alternatively in a repetitive manner. Examples of the inorganic material having a high refractive index include silicon nitride (Si3N4), titanium oxide (TiO2), and the like. Examples of the inorganic material having a low refractive index include silicon oxide (SiO2) and the like. It is possible to provide the multilayer film filter81, for example, between the organic photoelectric conversion section20and the interlayer insulating layer34.

In addition, it is also possible to obtain similar effects, for example, by providing a plasmon filter between the organic photoelectric conversion section20and the semiconductor substrate30.

FIG.5schematically illustrates a cross-sectional configuration of a photoelectric conversion element (photoelectric conversion element10D) according to a modification example 2 of the present disclosure. The photoelectric conversion element10D is included in the one unit pixel P in the imaging device (imaging device1) such as a CMOS image sensor that is able to capture, for example, an image obtained from visible light without using any color filter. The photoelectric conversion element10D according to the present modification example is a photoelectric conversion element of a so-called vertical spectral type in which, for example, the one organic photoelectric conversion section20and two inorganic photoelectric conversion sections32G and32R are stacked in the vertical direction.

The organic photoelectric conversion section20and inorganic photoelectric conversion sections32G and32R each selectively detect light in a different wavelength range and perform photoelectric conversion. Specifically, the organic photoelectric conversion section20acquires, for example, a color signal of blue (B). The inorganic photoelectric conversion sections32G and32R respectively acquire color signals of green (G) and red (R) by using different absorption coefficients. This allows an imaging device10to acquire a plurality of types of color signals in one pixel without using any color filter.

The inorganic photoelectric conversion sections32G and32R are formed to be buried in the semiconductor substrate30and are stacked in the thickness direction of the semiconductor substrate30. The second surface (front surface)30B of the semiconductor substrate30is provided, for example, with floating diffusions (floating diffusion layers) FD1, FD2, and FD3, transfer transistors Tr2 and Tr3, an amplifier transistor AMP, a reset transistor RST, a selection transistor SEL, and the multilayer wiring layer40.

For example, the interlayer insulating layer34and an insulating layer37are provided between the first surface30A of the semiconductor substrate30and the lower electrode21. The insulating layer37includes a layer (fixed electric charge layer)37A having fixed electric charge and a dielectric layer37B having an insulation property. There is provided a protective layer52on the upper electrode23. There are provided a planarization layer (not illustrated) and an optical member such as an on-chip lens layer53including an on-chip lens53L above the protective layer52.

In this way, the present technology is also applicable to an imaging device that captures a visible light image. In addition, in the present modification example, the photoelectric conversion element10D has been described in which the one organic photoelectric conversion section20and the two inorganic photoelectric conversion sections32R and32G are stacked, but the photoelectric conversion element according to the present technology may have a configuration in which, for example, two respective organic photoelectric conversion sections that detect the blue light (B) and the green light (G) and one inorganic photoelectric conversion section that detects the red light (R) are stacked.

FIG.6illustrates a cross-sectional configuration of a photoelectric conversion element (photoelectric conversion element10E) according to a modification example 3 of the present disclosure. The photoelectric conversion element10E is included in the one unit pixel P in the imaging device (imaging device1) such as a CMOS image sensor that is able to capture, for example, an image obtained from visible light without using any color filter as with the photoelectric conversion element10D according to the modification example 2 described above. The photoelectric conversion element10E according to the present modification example has a configuration in which a red photoelectric conversion section90R, a green photoelectric conversion section90G, and a blue photoelectric conversion section90B are stacked on the semiconductor substrate30in this order with an insulating layer96interposed in between.

The red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B respectively include organic photoelectric conversion layers92R,92G, and92B between pairs of electrodes. Specifically, the red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B respectively include the organic photoelectric conversion layers92R,92G, and92B between a first electrode91R and a second electrode93R, between a first electrode910and a second electrode93G, and between a first electrode91B and a second electrode93B.

There is provided an on-chip lens98L above the blue photoelectric conversion section90B with a protective layer97and an on-chip lens layer98interposed in between. There are provided a red electricity storage layer310R, a green electricity storage layer310G, and a blue electricity storage layer310B in the semiconductor substrate30. Light entering the on-chip lens98L is photoelectrically converted by the red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B and the signal charge is transmitted from the red photoelectric conversion section90R to the red electricity storage layer310R, from the green photoelectric conversion section90G to the green electricity storage layer310G, and from the blue photoelectric conversion section90B to the blue electricity storage layer310B. Although the signal charge may be electrons or holes generated by photoelectric conversion, the following gives description by exemplifying a case where electrons are read out as signal charge.

The semiconductor substrate30includes, for example, a p-type silicon substrate. The red electricity storage layer310R, the green electricity storage layer310G, and the blue electricity storage layer310B provided in this semiconductor substrate30each include an n-type semiconductor region and signal charge (electrons) supplied from the red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B is accumulated in these n-type semiconductor regions. The n-type semiconductor regions of the red electricity storage layer310R, the green electricity storage layer310G, and the blue electricity storage layer310B are formed, for example, by doping the semiconductor substrate30with an n-type impurity such as phosphorus (P) or arsenic (As). It is to be noted that the semiconductor substrate30may be provided on a support substrate (not illustrated) including glass or the like.

The semiconductor substrate30includes a pixel transistor for reading out electrons from the red electricity storage layer310R, the green electricity storage layer310G, and the blue electricity storage layer310B and transferring the read electrons, for example, to a vertical signal line (vertical signal line Lsig inFIG.2). The floating diffusion of this pixel transistor is provided in the semiconductor substrate30and this floating diffusion is coupled to the red electricity storage layer310R, the green electricity storage layer310G, and the blue electricity storage layer310B. The floating diffusion includes an n-type semiconductor region.

The insulating layer96includes, for example, silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiON), hafnium oxide (HfOx), and the like. The insulating layer96may include a plurality of types of insulating films that is stacked. The insulating layer96may include an organic insulating material. This insulating layer96is provided with plugs and electrodes for coupling the red electricity storage layer310R and the red photoelectric conversion section90R, the green electricity storage layer310G and the green photoelectric conversion section90G, and the blue electricity storage layer310B and the blue photoelectric conversion section90B.

The red photoelectric conversion section90R includes the first electrode91R, the organic photoelectric conversion layer92R, and the second electrode93R in this order from positions close to the semiconductor substrate30. The green photoelectric conversion section90G includes the first electrode91G, the organic photoelectric conversion layer92G, and the second electrode93G in this order from positions close to the red photoelectric conversion section90R. The blue photoelectric conversion section90B includes the first electrode91B, the organic photoelectric conversion layer92B, and the second electrode93B in this order from positions close to the green photoelectric conversion section90G. The insulating layer44is provided between the red photoelectric conversion section90R and the green photoelectric conversion section90G. There is provided an insulating layer95between the green photoelectric conversion section90G and the blue photoelectric conversion section90B. The red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B respectively absorb selectively red (e.g., a wavelength of 600 nm or more and less than 700 nm) light, green (e.g., a wavelength of 480 nm or more and less than 600 nm) light, and blue (e.g., a wavelength of 400 nm or more and less than 480 nm) light to generate electron/hole pairs.

The first electrode91R, the first electrode91G, and the first electrode91B respectively extract the signal charge generated in the organic photoelectric conversion layer92R, the signal charge generated in the organic photoelectric conversion layer92G, and the signal charge generated in the organic photoelectric conversion layer92B. The first electrodes91R.91G, and91B are provided, for example, for each of the pixels. Each of these first electrodes91R,91G, and91B includes, for example, an electrically conductive material having light transmissivity. Specifically, each of these first electrodes91R,91G, and91B includes ITO. Each of the first electrodes91R,91G, and91B may include, for example, a tin oxide-based material or a zinc oxide-based material. The tin oxide-based material is obtained by adding a dopant to tin oxide. Examples of the zinc oxide-based material include aluminum zinc oxide in which aluminum is added to zinc oxide as a dopant, gallium zinc oxide in which gallium is added to zinc oxide as a dopant, indium zinc oxide in which indium is added to zinc oxide as a dopant, and the like. In addition, it is also possible to use IGZO, CuI, InSbO4, ZnMgO, CuInO2, MgIn2O4, CdO, ZnSnO3, and the like.

For example, there may be provided electron transport layers between the first electrode91R and the organic photoelectric conversion layer92R, between the first electrode91G and the organic photoelectric conversion layer92G, and between the first electrode91B and the organic photoelectric conversion layer92B. The electron transport layers are for facilitating the electrons generated in the organic photoelectric conversion layers92R,92G, and92B to be supplied to the first electrodes91R,91G, and91B. Each of the electron transport layers includes, for example, titanium oxide, zinc oxide, or the like. Each of the electron transport layers may include titanium oxide and zinc oxide that are stacked.

Each of the organic photoelectric conversion layers92R,92G, and92B absorbs light in a selective wavelength range for photoelectric conversion and transmits light in another wavelength range. Here, the light in the selective wavelength range is light, for example, in the wavelength range of a wavelength of 600 nm or more and less than 700 nm in the organic photoelectric conversion layer92R, light, for example, in the wavelength range of a wavelength of 480 nm or more and less than 600 nm in the organic photoelectric conversion layer92G, and light, for example, in the wavelength range of a wavelength of 400 nm or more and less than 480 nm in the organic photoelectric conversion layer92B.

Each of the organic photoelectric conversion layers92R,92G, and92B has a configuration similar to that of the organic photoelectric conversion layer12according to the embodiment described above. For example, each of the organic photoelectric conversion layers92R,92G, and92B includes, for example, two or more types of organic semiconductor materials. It is preferable that each of the organic photoelectric conversion layers92R,92G, and92B include, for example, any one or both of a p-type semiconductor and an n-type semiconductor. For example, in a case where each of the organic photoelectric conversion layers92R,92G, and92B includes the two types of organic semiconductor materials of a p-type semiconductor and an n-type semiconductor, for example, one of the p-type semiconductor and the n-type semiconductor is preferably a material having transmissivity to visible light and the other thereof is preferably a material that photoelectrically converts light in a selective wavelength range. Alternatively, it is preferable that each of the organic photoelectric conversion layers92R,92G, and92B include the three types of organic semiconductor materials of a material (dye material) that photoelectrically converts light in a selective wavelength range and the n-type semiconductor and the p-type semiconductor each having transmissivity to visible light.

For example, it is preferable to use, for example, a material (dye material) that allows light in the wavelength range of a wavelength of 600 nm or more and less than 700 nm to be photoelectrically converted for the organic photoelectric conversion layer92R. Examples of such a material include subnaphthalocyanine or a derivative thereof and phthalocyanine or a derivative thereof. For example, it is preferable to use, for example, a material (dye material) that allows light in the wavelength range of a wavelength of 480 nm or more and less than 600 nm to be photoelectrically converted for the organic photoelectric conversion layer92G. Examples of such a material include subphthalocyanine or a derivative thereof or the like. It is preferable to use, for example, a material (dye material) that allows light in the wavelength range of a wavelength of 400 nm or more and less than 480 nm to be photoelectrically converted for the organic photoelectric conversion layer92B. Such a material includes the DTBDT derivative represented by the general formula (1) or the general formula (2) or the like. In addition, it may use, for example, a mixture of coumarin or a derivative thereof and porphyrin or a derivative thereof for the organic photoelectric conversion layer92B in addition to the materials described above.

For example, there may be provided hole transport layers between the organic photoelectric conversion layer92R and the second electrode93R, between the organic photoelectric conversion layer92G and the second electrode93G, and between the organic photoelectric conversion layer92B and the second electrode93B. The hole transport layers are for facilitating the holes generated in the organic photoelectric conversion layers92R,92G, and92B to be supplied to the second electrodes93R,93G, and93B. Each of the hole transport layers includes, for example, molybdenum oxide, nickel oxide, vanadium oxide, or the like. Each of the hole transport layers may include an organic material such as PEDOT (Poly(3,4-ethylenedioxythiophene) and TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine).

The second electrode93R, the second electrode93G, and the second electrode93B are for respectively extracting the holes generated in the organic photoelectric conversion layer92R, the holes generated in the organic photoelectric conversion layer92G, and the holes generated in the organic photoelectric conversion layer92G. The holes extracted from each of the second electrodes93R,93G, and93B are discharged, for example, to a p-type semiconductor region (not illustrated) in the semiconductor substrate30through each of the transmission paths (not illustrated). Each of the second electrodes93R.93G, and93B includes, for example, an electrically conductive material such as gold, silver, copper, and aluminum. As with the first electrodes91R,91G, and91B, each of the second electrodes93R,93G, and93B may include a transparent electrically conductive material. In the photoelectric conversion element10E, the holes extracted from these second electrodes93R.93G, and93B are discharged. For example, in a case where the plurality of photoelectric conversion elements10E is disposed in the imaging device1described below, the second electrodes93R,93G, and93B may be thus provided that are common between the respective photoelectric conversion elements10E (unit pixels P).

An insulating layer94is for insulating the second electrode93R and the first electrode91G. The insulating layer95is for insulating the second electrode93G and the first electrode91B. Each of the insulating layers94and95includes, for example, metal oxide, metal sulfide, or an organic substance. Examples of the metal oxide include silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, tungsten oxide, magnesium oxide, niobium oxide, tin oxide, gallium oxide, and the like. Examples of the metal sulfide include zinc sulfide, magnesium sulfide, and the like. It is preferable that the band gap of a material included in each of the insulating layers94and95be 3.0 eV or more.

As described above, the present technology is also applicable to a photoelectric conversion element (photoelectric conversion element10E) in which the red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B are stacked in this order. The red photoelectric conversion section90R, the green photoelectric conversion section90G, and the blue photoelectric conversion section90B include the respective photoelectric conversion layers (organic photoelectric conversion layers92R,92G, and92B). Each of the photoelectric conversion layers (organic photoelectric conversion layers92R,92G, and92B) includes an organic semiconductor material.

3. Application Examples

The imaging device1described above is applicable to any type of electronic apparatus having an imaging function, for example, a camera system such as a digital still camera and a video camera, a mobile phone having an imaging function, and the like.FIG.7illustrates a schematic configuration of an electronic apparatus1000.

The electronic apparatus1000includes the imaging device1, a DSP (Digital Signal Processor) circuit1001, a frame memory1002, a display unit1003, a recording unit1004, an operation unit1005, and a power supply unit1006. They are coupled to each other through a bus line1007.

The DSP circuit1001is a signal processing circuit that processes a signal supplied from the imaging device1. The DSP circuit1001outputs image data that is obtained by processing the signal from the imaging device1. The frame memory1002temporarily retains the image data processed by the DSP circuit1001in units of frames.

The display unit1003includes, for example, a panel-type display device such as a liquid crystal panel or an organic EL (Electro Luminescence) panel and records the image data of a moving image or a still image captured by the imaging device1in a recording medium such as a semiconductor memory or a hard disk.

The operation unit1005outputs an operation signal for a variety of functions of the electronic apparatus1000in accordance with an operation by a user. The power supply unit1006appropriately supplies the DSP circuit1001, the frame memory1002, the display unit1003, the recording unit1004, and the operation unit1005with various kinds of power for operations of these supply targets.

4. Practical Application Examples

Example of Practical Application to Endoscopic Surgery System

The technology (the present technology) according to the present disclosure is applicable to a variety of products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system.

FIG.9is a block diagram depicting an example of a functional configuration of the camera head11102and the CCU11201depicted inFIG.8.

The example of the endoscopic surgery system to which the technology according to the present disclosure may be applied has been described above. The technology according to the present disclosure may be applied to the image pickup unit11402among the components described above. The application of the technology according to the present disclosure to the image pickup unit11402increases the detection accuracy.

It is to be noted that the endoscopic surgery system has been described here as an example, but the technology according to the present disclosure may be additionally applied, for example, to a microscopic surgery system or the like.

Example of Practical Application to Mobile Body

The technology according to the present disclosure is applicable to a variety of products. For example, the technology according to the present disclosure may be achieved as a device mounted on any type of mobile body such as a vehicle, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a vessel, a robot, a construction machine, or an agricultural machine (tractor).

5. Working Examples

Next, working examples of the present disclosure are described in detail. In an experiment 1, the compound represented by the formula (0-1) described above and the thin film of the organic photoelectric conversion layer22described above were formed as the hole transporting material that absorbs blue light and the spectral characteristics thereof were evaluated. In an experiment 2, the crystallizability of the thin film described above was evaluated. In the experiment 2, the crystal structure of the compound represented by the formula (1-1) described above was evaluated. In an experiment 4, a device sample including the organic photoelectric conversion layer22described above was fabricated and the electric characteristics thereof were evaluated.

Experiment 1: Evaluation of Spectral Characteristics of Thin Film

A sample for evaluating spectral characteristics was fabricated by using the following method. First, a quartz glass substrate cleaned in UV/ozone treatment was moved to a vacuum evaporation device and a film of the compound represented by the formula (1-1) was formed at a substrate temperature of 0° C. under a reduced pressure condition of 1×10−5Pa or less by using a resistive heating method while a substrate holder was rotated. Evaporation was performed at an evaporation speed of 0.1 nm/second to offer a film thickness of 50 nm (experimental example 1-1). Similarly, a film of the compound (rBDT) (experimental example 1-2) represented by the following formula (5) that was usable as the hole transporting material was formed as with the compound represented by the formula (1-1). In addition, along with the compound represented by the formula (1-1) and the compound represented by the formula (5), films of the subphthalocyanine (SubPc) (experimental example 1-3) represented by the following formula (6) and the fullerene Co (experimental example 1-4) represented by the formula (3) described above that were used as materials of an organic photoelectric conversion layer were formed.

In addition, similarly, a thin film (experimental example 1-5) including the three types of organic materials of the compound represented by the formula (1-1), subphthalocyanine (SubPc), and a fullerene C60was formed. The respective evaporation speeds were 0.5 nm/second, 0.5 nm/second, and 0.25 nm/second and the film thickness was 200 nm. Similarly, a thin film (experimental example 1-6) including the three types of organic materials of the compound (rBDT) represented by the formula (5), subphthalocyanine (SubPc), and a fullerene Co was formed. The respective evaporation speeds were 0.5 nm/second, 0.5 nm/second, and 0.25 nm/second and the film thickness was 200 nm. These experimental example 1-5 and experimental example 1-6 were used as samples for evaluating the spectral characteristics of the ternary organic photoelectric conversion layer.

In addition, similarly, a thin film (experimental example 1-7) including the two types of organic materials of the compound represented by the formula (1-1) and subphthalocyanine (SubPc) was formed. The respective evaporation speeds were 0.5 nm/second and 0.5 nm/second and the film thickness was 100 nm. Similarly, a thin film (experimental example 1-8) including the two types of organic materials of the compound (rBDT) represented by the formula (5) and subphthalocyanine (SubPc) was formed. The respective evaporation speeds were 0.5 nm/second and 0.5 nm/second and the film thickness was 100 nm. These experimental example 1-7 and experimental example 1-8 were used as samples for evaluating the spectral characteristics of the binary organic photoelectric conversion layer.

As the spectral characteristics, the absorptivity (%) of light absorbed by each thin film was obtained by measuring the transmittance and the reflectance of the wavelength region corresponding to a wavelength λ=350 to 700 nm for each of the wavelengths with an ultraviolet and visible spectrophotometer. A linear absorption coefficient α (cm−1) of each thin film for each wavelength was evaluated on the basis of the Lambert-Beer law by using this absorptivity of light and the film thickness of the thin film as parameters. λmax(nm) was the wavelength observed on the longest wavelength among the wavelengths indicating the maximum value of the linear absorption coefficient observed in a certain absorption spectrum.

FIG.12illustrates the absorption spectra of a thin film (experimental example 1-1) including the compound represented by the formula (1-1) and a thin film (experimental example 1-2) including the compound (rBDT) represented by the formula (5).FIG.13illustrates the absorption spectra of a thin film (experimental example 1-3) including the experimental example 1-1 and subphthalocyanine (SubPc) and a thin film (experimental example 1-4) including a fullerene C60.FIG.14illustrates the absorption spectra of thin films included in the temary organic photoelectric conversion layer of the experimental example 1-5 and the experimental example 1-6 described above.FIG.15illustrates the absorption spectra of thin films included in the binary organic photoelectric conversion layer of the experimental example 1-7 and the experimental example 1-8 described above.

FIG.12illustrates that the compound represented by the formula (1-1) has a higher linear absorption coefficient in the region of λ=350 to 500 nm than that of the compound (rBDT) represented by the formula (5). In other words, it has been found that the compound represented by the formula (1-1) is a hole transporting material having increased light absorption ability. For example, a in λ=450 nm was 7.3×104cm−1for the compound represented by the formula (1-1) and 0.5×104cm−1for the compound (rBDT) represented by the formula (5). In other words, it has been found that the light absorption ability of the compound represented by the formula (1-1) is increased 15 times on this wavelength. Further, it has been found that α of the compound represented by the formula (5) is substantially 0 in λ=450 to 500 nm and no light is absorbed. Meanwhile, the compound represented by the formula (1-1) exhibits light absorption in even this wavelength range. This indicates that the compound represented by the formula (1-1) is a material having higher light absorption ability than that of the compound (rBDT) represented by the formula (5).

FIG.13illustrates that the compound represented by the formula (1-1), subphthalocyanine (SubPc), and a fullerene C60each efficiently absorb a different wavelength region. For example, it has been found that a of the compound represented by the formula (1-1) is the highest in the blue region of 400 nm to 430 nm and light within this range is efficiently absorbed. It has been found that α of subphthalocyanine (SubPc) is the highest in the green region of 500 nm to 580 nm and light within this range is efficiently absorbed. It has been found that α of a fullerene C60is the highest in the red region of 600 nm to 650 nm and light within this range is efficiently absorbed.

In addition, Table 1 tabulates λmax(nm) of the compound represented by the formula (1-1), subphthalocyanine (SubPc), and a fullerene C60. Table 1 indicates that the compound represented by the formula (1-1), subphthalocyanine (SubPc), and a fullerene C60are different from each other in λmax(nm). Among them, λmax of the compound represented by the formula (1-1) is the shortest wavelength.

The above indicates that the three types of organic materials which form the temary organic photoelectric conversion layer22each absorb light in a different wavelength region and this is effective to increase the light absorption ability of the organic photoelectric conversion layer. This can also be seen fromFIG.14.

In addition,FIG.14illustrates that, in a case where the compound represented by the formula (1-1) is used as a hole transporting material, even a binary organic photoelectric conversion layer has a larger optical absorption coefficient within a range of 350 nm to 500 nm than the use of the compound (rBDT) represented by the formula (5). As can be seen fromFIG.12, this is derived from the higher optical absorption coefficient of the compound represented by the formula (1-1) within a range of 350 nm to 500 nm than that of the compound (rBDT) represented by the formula (5). In other words, it has been found that the use of the compound represented by the formula (1-1) that has high light absorption ability as a hole transporting material allows the temary organic photoelectric conversion layer22to have a panchromatic spectral shape. It is to be noted that a hole transporting material serves to absorb light in the blue region, a dye serves to absorb light in the green region, and an electron transport material serves to absorb light in the red region in this organic photoelectric conversion layer22(experimental example 1-5).

Further,FIG.15illustrates that, in a case where the compound represented by the formula (1-1) is used as a hole transporting material, the optical absorption coefficient within a range of 350 nm to 500 nm is larger than the use of the compound represented by the formula (5). As with the temary organic photoelectric conversion layer (experimental example 1-5), this is derived from the higher optical absorption coefficient of the compound represented by the formula (1-1) within a range of 350 nm to 500 nm than that of the compound represented by the formula (5). In other words, it has been found that the use of the compound represented by the formula (1-1) that has high light absorption ability as a hole transporting material allows the binary organic photoelectric conversion layer22to have a panchromatic spectral shape. It is to be noted that a hole transporting material serves to absorb light in the blue region and a dye serves to absorb light in the green region in this organic photoelectric conversion layer22(experimental example 1-7).

Experiment 2: Evaluation of Crystallizability of Thin Film

A sample for evaluating the crystallizability of a thin film was fabricated by using the following method. First, an ITO film having a thickness of 50 nm was formed on a glass substrate by using a sputtering device. This ITO film was patterned by photolithography and etching and used as an ITO electrode. Subsequently, the glass substrate provided with the ITO electrode was cleaned in UV/ozone treatment and a film of the compound represented by the formula (1-1) was then formed by a vacuum evaporation device at a substrate temperature of 20° C. under a reduced pressure condition of 1×10−5Pa or less in a resistive heating method while a substrate holder was rotated. Evaporation was performed at a vacuum evaporation speed of 0.1 nm/second to offer a film thickness of 50 nm. This was used as a sample for evaluating the crystallizability of a thin film of the compound represented by the formula (1-1) (experimental example 2-1).

Similarly, the compound represented by the formula (1-1), subphthalocyanine (SubPc) and a fullerene C60were co-evaporated on a glass substrate in a resistive heating method at a substrate temperature of 20° C. under a reduced pressure condition of 1×10−5Pa or less by a vacuum evaporation device while a substrate holder was rotated. The glass substrate had been cleaned in UV/ozone treatment. The glass substrate had a film thickness of 50 nm and was provided with the ITO electrode. The respective evaporation speeds were 0.5 nm/second, 0.5 nm/second, and 0.25 nm/second and the film thickness was 230 nm. This was used as a sample for evaluating the crystallizability of a ternary thin film (experimental example 2-2).

To evaluate the crystallizability of the thin film described above, an X-ray diffraction device whose X-ray source was CuKα was used for X-ray radiation and the X-ray diffraction in the out-of-plane direction was measured within the range of 20=2 to 30° by using a grazing incidence method.

FIG.16illustrates the X-ray diffraction pattern of a thin film (experimental example 2-1) including the compound represented by the formula (1-1).FIG.17illustrates the X-ray diffraction pattern of a thin film (experimental example 2-2) including the compound represented by the formula (1-1), subphthalocyanine (SubPc), and a fullerene C60.

It has been found that any of the samples has about three clear peaks within the range of 20=18 to 29°. In addition, no peaks were confirmed in the other regions of any of the samples. Further.FIG.16illustrates these three clear peaks. This indicates that these peaks are derived from the compound represented by the formula (1-1). In other words, it has been found that the compound represented by the formula (1-1) has crystallizability in a case of a thin film. In addition,FIG.17illustrates these peaks at similar positions. This indicates that the compound represented by the formula (1-1) also has crystallizability in a ternary organic photoelectric conversion layer.

In addition, the peak positions and the crystallite sizes of the experimental example 2-1 and the experimental example 2-2 were evaluated by using the following method. The following defines the three clear peaks as a first peak, a second peak, and a third peak in order from the low angle side.

The respective peak positions of the first peak, the second peak, and the third peak were obtained by fitting the respective peaks from the spectrum subjected to background subtraction with the Pearson VII function. The crystallite size was obtained by fitting the second peak with the Pearson VII function to obtain the half width thereof and substituting the half width into the Scherrer's equation. In this case, 0.94 was used as a Scherrer constant K.

Table 2 tabulates the respective peak positions and crystallite sizes of the first peak, the second peak and the third peak.

The peak positions of the first peaks, the peak positions of the second peaks, and the peak positions of the third peaks of a thin film (experimental example 2-1) of the compound represented by the formula (1-1) and a temary thin film (experimental example 2-2) were respectively 19.0° and 19.0°, 23.4° and 23.4°, and 27.9° and 27.9°. The peak positions of the first peaks, the second peaks, and the third peaks are not changed between the experimental example 2-1 and the experimental example 2-2. This means that the first peaks, the second peaks, and the third peaks are each derived from the compound represented by the formula (1-1). The crystallite sizes of the experimental example 2-1 and the experimental example 2-2 were respectively 13.8 nm and 15.2 nm for the first peaks, 10.9 nm and 16.7 nm for the second peaks, and 10.5 nm and 12.8 nm for the third peaks. It has been found that the ternary thin film generally increases in particle size. This indicates that the compound represented by the formula (1-1) is a stable material that does not change the crystallizability even in a case where the compound is mixed with another material and serves as a co-evaporation film.

Experiment 3: Evaluation of Crystal Structure

An experiment 3 studied what molecular arrangement feature of the compound represented by the formula (1-1) caused the first peak, the second peak, and the third peak observed in the experiment 2.

As a sample for evaluating a crystal structure, a single crystal of the compound represented by the formula (1-1) that had the shape of a block of 0.13 mm 0.09 mm×0.07 mm was fabricated in a sublimination purification method. For this sample, an X-ray structural analysis in which a MoKα ray having a wavelength of 0.71073 Å was used as an X-ray source was conducted by using XtaLab AFC11 (RINC).14584reflections in total were measured within the range of θ=2.067 to 27.484°. The structure was solved in the direct method SIR-2004 by using the collected pieces of diffraction data. Structural optimization was performed in a least square method for a structure factor F2. From a result of the structural optimization obtained, the powder X-ray diffraction pattern was obtained in a case where CuKα was used as an X-ray source.

Table 3 tabulates the crystal data and a result of the structure optimization of the compound represented by the formula (1-1).FIG.18illustrates the molecular arrangement of the compound represented by the formula (1-1) viewed from the c axis.FIG.19simulates the powder X-ray diffraction pattern of the compound represented by the formula (1-1) in a case where CuKα is used as an X-ray source.

Table 3 indicates that an R1 factor obtained as a result of structural optimization is 6.28%. This indicates that it is possible to analyze the structure of the compound represented by the formula (1-1) without any problem.

FIG.18indicates that the compound represented by the formula (1-1) has a molecular arrangement referred as herringbone. In the a axis direction, there are an interaction and π-π stacking caused by the overlapping π-electrons of the skeleton of the compound represented by the formula (1-1). In the b axis direction, there is a CH-π interaction caused by the interaction between the hydrogen atoms of the skeleton of the compound represented by the formula (1-1) and the n-electrons of the skeleton. The presence of these interactions causes the compound represented by the formula (1-1) to form a molecular arrangement referred to as herringbone.

As the simulation result ofFIG.19, intense diffraction peaks were confirmed at the three of 19.03°, 23.67°, and 28.09° in a case where CuKα was used as an X-ray source. These three respective diffraction peaks correspond to the diffraction peaks from the plane orientation (111), (020), and (121). All of these diffraction peaks are peaks indicating the formation of a herringbone structure. It has been thus found that, in a case of the thin film and the temary thin film, the compound represented by the formula (1-1) has a herringbone structure in each of the films.

In addition, with respect to the photoelectric conversion element, a hole transporting material having a herringbone structure in the organic photoelectric conversion layer causes molecules to be located at spatially closer positions than those of a randomly dispersed hole transporting material. This makes it expectable to increase the electric charge transporting property in the organic photoelectric conversion layer.

Experiment 4: Evaluation of Electric Characteristics

Next, a device sample for evaluating electric characteristics was fabricated by using the following method and the dark current characteristics and external quantum efficiency (EQE) thereof were evaluated.

First, as an experimental example 3-1, an ITO film having a thickness of 100 nm was formed on a quartz glass substrate by using a sputtering device. This ITO film was patterned by photolithography and etching and used as an ITO electrode. Subsequently, the quartz glass substrate provided with the ITO electrode was cleaned in UV/ozone treatment and the quartz glass substrate was then moved to a vacuum evaporation device. A film of the electron blocking material represented by the following formula (7) was formed at an evaporation speed of 1 Å/sec by using a resistive heating method to have a thickness of 5 nm and form an electron block layer while a substrate holder was rotated under a reduced pressure condition of 1×10−5Pa or less. Next, as an organic photoelectric conversion layer, films of a C60fullerene (formula (3) described above), the subphthalocyanine (SubPc) represented by the following formula (6), and the compound represented by the following formula (1-1) were formed at a substrate temperature of 20° C. at respective film formation rates of 0.025 nm/second, 0.050 nm/second, and 0.050 nm/second to offer 230 nm as the thickness of the mixture layer. This offered an organic photoelectric conversion layer having a composition ratio of 20 vol % (C60fullerene):40 vol % (SubPc):40 vol % (formula (1-1)). Subsequently, a film of the hole blocking material represented by the following formula (8) was formed at an evaporation speed of 0.3 Å/sec to have a thickness of 5 nm and form a hole block layer Finally, an AlSiCu film was formed on the hole block layer in an evaporation method to have a film thickness of 100 nm and this was used as an upper electrode. A photoelectric conversion element (experimental example 3-1) including a photoelectric conversion region of 1 mm×1 mm was fabricated in the fabricating method described above.

In addition, as an experimental example 3-2, the compound (rBDT) represented by the formula (5) was used as a hole transporting material in place of the compound represented by the formula (1-1) to fabricate a photoelectric conversion element (experimental example 3-2) by using a method similar to that of the experimental example 3-1.

The EQE and the dark current characteristics were evaluated by using a semiconductor parameter analyzer. Specifically, specifically, a current value (light current value) obtained in a case where a photoelectric conversion element was irradiated with an amount of light corresponding to 1.62 μW/cm2from a light source through a filter and a bias voltage of −2.6 V was applied between electrodes and a current value (dark current value) obtained in a case where the amount of light was set to 0 μW/cm2were each measured. The EQE and the dark current characteristics were calculated from these values. As the wavelength of the light with which the element was irradiated, the wavelength corresponding to the maximum absorption wavelength of each organic photoelectric conversion layer in the visible range was selected. The selected irradiation wavelength of light was 560 nm in any of the experimental example 3-1 and the experimental example 3-2.

Table 4 tabulates the EQE and the dark current characteristics of the experimental example 3-1 and the experimental example 3-2. The numerical values of the experimental example 3-1 are relative values in a case where the experimental example 3-2 is used as a reference (1.0). A result thereof indicates that the experimental example 3-1 has EQE equivalent to that of the experimental example 3-2 and more favorable dark current characteristics than those of the experimental example 3-2. This indicates that the use of the compound represented by the formula (1-1) as a material included in the organic photoelectric conversion layer offers favorable EQE and dark current characteristics.

In addition, a result of the experiment 1 indicates that the organic photoelectric conversion layer of the experimental example 3-1 is able to absorb the wavelength of a wide region. These results indicate that the use of the compound represented by the general formula (1) or the general formula (2) as a material included in the organic photoelectric conversion layer makes it possible to fabricate a photoelectric conversion element that has excellent electric characteristics and has high light absorption ability.

Although the description has been given with reference to the embodiment, the modification examples 1 to 3, the working examples, the application examples, and the practical application examples, the contents of the present disclosure are not limited to the embodiment and the like described above. The present disclosure may be modified in a variety of ways. For example, the components, disposition, numbers, and the like of the photoelectric conversion elements10A or the like exemplified in the embodiment and the like described above are merely examples. Not all of the components have to be provided. In addition, other components may be further included.

In the embodiment and the like described above, the example has been described in which the organic photoelectric conversion section20that detects the visible light region and the inorganic photoelectric conversion section32that detects light in the infrared light region are stacked, but it is also possible to use the organic photoelectric conversion section20alone.

In addition, in the embodiment and the like described above, the example has been described in which the lower electrode21includes one electrode, but two or three or more electrodes may be used. Further, the present technology has been described in the embodiment and the like described above with reference to a so-called back-illuminated image sensor as an example in which the front (second surface30B) side of the semiconductor substrate30is provided with the multilayer wiring layer40and light comes from the back surface (first surface30A) side, but the present technology is also applicable to a front-illuminated image sensor.

Still further, in the modification example 2 described above, the example has been described in which the red light (R) and the green light (G) are detected in the semiconductor substrate30and the blue light (B) is detected above this semiconductor substrate30as the photoelectric conversion element10D that detects the visible light region, but this is not limitative. For example, the red light (R) may be detected in the semiconductor substrate30and there may be provided two respective organic photoelectric conversion sections that detect the green light (G) and the blue light (B) above this semiconductor substrate30.

It is to be noted that the effects described herein are merely examples, but are not limitative. In addition, there may be other effects.

It is to be noted that the present disclosure may also have configurations as follows. According to the present technology having the following configurations, the photoelectric conversion layer is formed by using the hole transporting material that absorbs blue light as the first organic semiconductor material. This makes it possible to extend the absorption spectrum of the photoelectric conversion layer and provide a photoelectric conversion element and an imaging device each having a wide absorption spectrum.

A photoelectric conversion element including:a first electrode;a second electrode that is disposed to be opposed to the first electrode; anda photoelectric conversion layer that is provided between the first electrode and the second electrode, the photoelectric conversion layer including a hole transporting material as a first organic semiconductor material, the hole transporting material absorbing blue light.
[2]

The photoelectric conversion element according to [1], in whichthe photoelectric conversion layer includes a plurality of organic semiconductor materials each having a different absorption maximum wavelength, andan absorption maximum wavelength of the hole transporting material is shortest among the plurality of organic semiconductor materials.
[3]

The photoelectric conversion element according to [1] or [2], in which the hole transporting material has crystallizability.

The photoelectric conversion element according to any of [1] to [3], in which the hole transporting material has a herringbone-type molecular arrangement.

The photoelectric conversion element according to any of [1] to [4], in which the photoelectric conversion layer further includes a second organic semiconductor material having an absorption maximum wavelength different from an absorption maximum wavelength of the first organic semiconductor material.

The photoelectric conversion element according to any of [1] to [4], in which the photoelectric conversion layer further includes a third organic semiconductor material having an absorption maximum wavelength different from an absorption maximum wavelength of the first organic semiconductor material.

The photoelectric conversion element according to any of [1] to [4], in which the photoelectric conversion layer includes a second organic semiconductor material and a third organic semiconductor material, the second organic semiconductor material and the third organic semiconductor material each having an absorption maximum wavelength different from an absorption maximum wavelength of the first organic semiconductor material.

The photoelectric conversion element according to [7], in whichthe first organic semiconductor material, the second organic semiconductor material, and the third organic semiconductor material each have a different absorption maximum wavelength, andthe absorption maximum wavelength of the first organic semiconductor material is shortest.
[9]

The photoelectric conversion element according to any of [5] to [8], in whichthe second organic semiconductor material includes a fullerene or a fullerene derivative, andthe first organic semiconductor material has a shallower Highest Occupied Molecular Orbital (HOMO) level than a HOMO level of the second organic semiconductor material.
[10]

The photoelectric conversion element according to any of [1] to [9], in which the hole transporting material includes a dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene derivative represented by the following general formula (1) or general formula (2).

The photoelectric conversion element according to any of [1] to [9], in which the hole transporting material includes compounds represented by the following formula (1-1) to formula (1-5).

An imaging device includinga plurality of pixels that is each provided with photoelectric conversion elements as one or more organic photoelectric conversion sections, in whichthe photoelectric conversion elements each includea first electrode,a second electrode that is disposed to be opposed to the first electrode, anda photoelectric conversion layer that is provided between the first electrode and the second electrode, the photoelectric conversion layer including a hole transporting material as a first organic semiconductor material, the hole transporting material absorbing blue light.
[13]

The imaging device according to [12], in which the one or more organic photoelectric conversion sections and one or more inorganic photoelectric conversion sections are stacked in each of the pixels, the one or more inorganic photoelectric conversion sections each performing photoelectric conversion in a wavelength range different from a wavelength range of each of the organic photoelectric conversion sections.

The imaging device according to [13], in whichthe inorganic photoelectric conversion sections are formed to be buried in a semiconductor substrate, andthe organic photoelectric conversion sections are formed on a first surface side of the semiconductor substrate.
[15]

The imaging device according to [14], in which the semiconductor substrate has a second surface opposed to the first surface and has a multilayer wiring layer formed on the second surface side.

The imaging device according to any of [13] to [15], in whichthe organic photoelectric conversion sections each perform photoelectric conversion in a visible light region, andthe inorganic photoelectric conversion sections each perform photoelectric conversion in an infrared light region.
[17]

The imaging device according to any of [12] to [16], in which a plurality of the organic photoelectric conversion sections is stacked in each of the pixels, the plurality of the organic photoelectric conversion sections each performing photoelectric conversion in a different wavelength range.

This application claims the priority on the basis of Japanese Patent Application No. 2019-200097 filed with Japan Patent Office on Nov. 1, 2019, the entire contents of which are incorporated in this application by reference.