Patent Description:
The present invention relates to display technology, more particularly, to a top-emission type organic light emitting diode display substrate, a top-emission type organic light emitting diode display apparatus, and a method of forming a top-emission type organic light emitting diode display substrate.

Organic light emitting diode (OLED) display apparatuses are self-emissive devices, and do not require backlights. OLED display apparatuses also provide more vivid colors and a larger color gamut as compared to the conventional liquid crystal display (LCD) apparatuses. Further, OLED display apparatuses can be made more flexible, thinner, and lighter than a typical LCD.

An OLED display apparatus typically includes an anode, an organic layer including an organic light emitting layer, and a cathode. OLEDs can either be a bottom-emission type OLED or a top-emission type OLED. In bottom-emission type OLEDs, the light is extracted from an anode side. In bottom-emission type OLEDs, the anode is generally transparent, while a cathode is generally reflective. In a top-emission type OLED, light is extracted from a cathode side. The cathode is optically transparent, while the anode is reflective. <CIT> provides an electro-optical apparatus including an element substrate that includes a display region in which a plurality of light-emitting elements are arranged, and a peripheral region in which a terminal is disposed. The light-emitting element has a structure in which a reflective electrode, an optical adjustment layer, a first electrode, a light-emitting layer, and a second electrode are laminated, and the first electrode is electrically connected to a contact electrode. The terminal has a structure in which a first terminal layer that is formed by a first conductive film which is the same as the reflective electrode, a second terminal layer that is formed by a second conductive film which is the same as the contact electrode, and a third terminal layer that is formed by a third conductive film which is the same as the first electrode are laminated. <CIT> provides an OLED(Organic Light Emitting Diode) display device and a manufacturing method thereof to reduce the number of processes and process costs by forming the same electroluminescent layer on magenta, red, blue, and green light emitting cells. The constitution is that first to third light emitting cells emit red light and blue light and include the same cell structure. A fourth light emitting cell emits green light and has a different structure from the first to third light emitting cells. A first color filter(RCF) is formed on the second light emitting cell. A first color filter blocks the blue light and transmits the red light. A second color filter(BCF) is formed on a third light emitting cell. The second color filter transmits the blue light and blocks the red light. <CIT> provides a structure of a light-emitting device that can make the foregoing planarization easier. The same layer as a wiring formed on a first film is used to manufacture a second film. Herewith, a portion of the first film below a light-emitting element can be prevented from being etched to form unevenness at a surface of the first film during the formation of the wiring. In addition, a surface of a third film is made higher by providing the second film to enable local planarization. <CIT> provides an OLED display element, its manufacturing method and a display device. The OLED display element includes a light-emitting pixel unit. The light-emitting unit includes an anode arranged above a base substrate, a cathode arranged opposite to the anode, and a micro cavity formed between the anode and the cathode. The micro cavity includes an organic light-emitting layer, and the anode includes an ITO layer arranged opposite to the cathode and a metal oxide conductor layer arranged at a side of the ITO layer that is farther away from the cathode than the other side of the ITO layer. <CIT> provides a light emitting device, which includes a transistor, a light reflection layer, a first insulation layer that includes a first layer thickness part, a second layer thickness part, and a third layer thickness part, a pixel electrode that is provided on the first insulation layer, a second insulation layer that covers a peripheral section of the pixel electrode, a light emission functional layer, a facing electrode, and a conductive layer that is provided on the first layer thickness part. The pixel electrode includes a first pixel electrode which is provided in the first layer thickness part, a second pixel electrode which is provided in the second layer thickness part, and a third pixel electrode which is provided in the third layer thickness part. The first pixel electrode, the second pixel electrode, and the third pixel electrode are connected to the transistor through the conductive layer.

The present invention is defined in independent claims <NUM> and <NUM>. Further aspects of the invention are defined in the dependent claims.

Optionally, an orthographic projection of the drain electrode on the base substrate substantially covers or overlaps with that of a light emitting region of the organic light emitting layer.

Optionally, the orthographic projection of the drain electrode on the base substrate substantially covers or overlaps with that of the first electrode layer.

Optionally, the drain electrode is made of a low-reflectivity metal material, such as molybdenum or nickel.

Optionally, the second electrode is made of a metallic material, such as magnesium:silver alloy.

Optionally, the first electrode has a thickness in a range of approximately <NUM>Å (ie. <NUM>) to approximately <NUM>Å.

Optionally, the planarization layer has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å.

Optionally, forming the second electrode is performed by a vapor deposition process.

The disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of some embodiments are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

To enhance aperture ratio of conventional organic light emitting diode display apparatus, typically a top-emission type organic light emitting diode display substrate is used. In the conventional top-emission type organic light emitting diode display substrate, relatively strong microcavity effects are observed. In the conventional display substrate, the anode and the cathode constitute two reflective mirrors of the microcavity. The optical distance of the microcavity is relatively small resulting in relatively strong microcavity effects. Due to the strong microcavity effects, light emitted from the conventional top-emission type organic light emitting diode display substrate has a narrow spectrum. Thus, the microcavity effects make it very difficult to achieve a full-spectrum light emission in the conventional top-emission type organic light emitting diode display substrate. The performance and light emission quality of the conventional organic light emitting diode display apparatus are limited.

Accordingly, the present disclosure provides, inter alia, a top-emission type organic light emitting diode display substrate, a top-emission type organic light emitting diode display apparatus, and a method of forming a top-emission type organic light emitting diode display substrate that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. The top-emission type organic light emitting diode display substrate is configured to emit light substantially along a direction from the first electrode to the second electrode.

As used herein, the term "subpixel area" refers to an area in an array substrate corresponding to a subpixel in a display panel having the array substrate. A subpixel area includes a subpixel region and an inter-subpixel region. As used herein, the term "substantially transparent" mean at least <NUM> percent (e.g., at least <NUM> percent, at least <NUM> percent, at least <NUM> percent, at least <NUM> percent, and at least <NUM> percent) of light in the visible wavelength range transmitted therethrough.

<FIG> is a schematic diagram illustrating the structure of a top-emission type organic light emitting diode display substrate in some embodiments according to the present disclosure. Referring to <FIG>, the top-emission type organic light emitting diode display substrate in some embodiments includes a base substrate <NUM>, a thin film transistor <NUM> on the base substrate <NUM>, a passivation layer <NUM> on a side of the thin film transistor <NUM> distal to the base substrate <NUM>, and an organic light emitting diode <NUM> on a side of the passivation layer <NUM> distal to the thin film transistor <NUM>. The thin film transistor <NUM> in some embodiments includes, inter alia, a drain electrode <NUM>, an active layer <NUM>, and a gate electrode <NUM>. The drain electrode <NUM> is electrically connected to a drain electrode contact region of the active layer <NUM>. Optionally, the organic light emitting diode <NUM> is on a side of the passivation layer <NUM> distal to the drain electrode <NUM>.

In some embodiments, the organic light emitting diode <NUM> includes a first electrode <NUM> on a side of the passivation layer <NUM> distal to the drain electrode <NUM>, an organic layer <NUM> on a side of the first electrode <NUM> distal to the passivation layer <NUM>, and a second electrode <NUM> on a side of the organic layer <NUM> distal to the first electrode <NUM>. Optionally, the top-emission type organic light emitting diode display substrate is configured to emit light substantially along a direction from the first electrode <NUM> to the second electrode <NUM>. The first electrode <NUM> is electrically connected to the drain electrode <NUM>. Optionally, the first electrode <NUM> is a substantially transparent electrode. Optionally, the first electrode <NUM> is an anode of the organic light emitting diode <NUM>, and the second electrode <NUM> is a cathode of the organic light emitting diode <NUM>.

The organic layer <NUM> in some embodiments includes an organic light emitting layer 11a. The organic light emitting layer 11a has a light emitting region E, as shown in <FIG>. In some embodiments, an orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially covers that of a light emitting region E of the organic light emitting layer 11a. Optionally, the orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially overlaps with that of the light emitting region E of the organic light emitting layer 11a. Optionally, the orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially covers that of the organic light emitting layer 11a. Optionally, the orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially overlaps with that of the organic light emitting layer 11a. Optionally, a width of the drain electrode <NUM> is substantially equal to or greater than that of the light emitting region E of the organic light emitting layer 11a. Optionally, a width of the drain electrode <NUM> is substantially equal to or greater than that of the organic light emitting layer 11a. Optionally, the orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially covers that of the first electrode layer <NUM>. Optionally, the orthographic projection of the drain electrode <NUM> on the base substrate <NUM> substantially overlaps with that of the first electrode layer <NUM>. Optionally, the width of the drain electrode <NUM> is substantially equal to or greater than that of the first electrode layer <NUM>. Optionally, the width of the drain electrode <NUM> is substantially equal to that of the first electrode layer <NUM>. Optionally, the width of the drain electrode <NUM> is substantially equal to that of the second electrode layer <NUM>.

<FIG> is a schematic diagram illustrating the structure of an organic layer in some embodiments according to the present disclosure. Referring to <FIG> and <FIG>, the organic layer <NUM> in some embodiments includes a first hole injection layer <NUM> on the first electrode <NUM>, a second hole injection layer <NUM> on a side of the first hole injection layer <NUM> distal to the first electrode <NUM>, a red light emitting layer <NUM> on a side of the second hole injection layer <NUM> distal to the first hole injection layer <NUM>, a green light emitting layer <NUM> on a side of the red light emitting layer <NUM> distal to the second hole injection layer <NUM>, a first electron transport layer <NUM> on a side of the green light emitting layer <NUM> distal to the red light emitting layer <NUM>, a first charge generating layer <NUM> on a side of the first electron transport layer <NUM> distal to the green light emitting layer <NUM>, a third hole injection layer <NUM> on a side of the first charge generating layer <NUM> distal to the first electron transport layer <NUM>, a hole transport layer <NUM> on a side of the third hole injection layer <NUM> distal to the first charge generating layer <NUM>, a blue light emitting layer <NUM> on a side of the hole transport layer <NUM> distal to the third hole injection layer <NUM>, a second electron transport layer <NUM> on a side of the blue light emitting layer <NUM> distal to the hole transport layer <NUM>, and a second charge generating layer <NUM> on a side of the second electron transport layer <NUM> distal to the blue light emitting layer <NUM>.

Referring to <FIG>, the top-emission type organic light emitting diode display substrate in some embodiments further includes a buffer layer <NUM> between the active layer <NUM> and the base substrate <NUM>. Optionally, the top-emission type organic light emitting diode display substrate further includes a gate insulating layer <NUM> between the gate electrode <NUM> and the active layer <NUM>. Optionally, the top-emission type organic light emitting diode display substrate further includes an inter-layer dielectric layer <NUM> between the gate electrode <NUM> and the drain electrode <NUM>. Optionally, the top-emission type organic light emitting diode display substrate further includes a source electrode in a same layer as the drain electrode <NUM>. Optionally, the top-emission type organic light emitting diode display substrate further includes a protective layer <NUM> on a side of the second electrode <NUM> distal to the base substrate <NUM>.

In some embodiments, the top-emission type organic light emitting diode display substrate further includes a planarization layer <NUM> on a side of the drain electrode <NUM> distal to the base substrate <NUM>. Optionally, the passivation layer <NUM> is on a side of the planarization layer <NUM> distal to the drain electrode <NUM>. Optionally, the planarization layer <NUM> and the passivation layer <NUM> are between the drain electrode <NUM> and the first electrode <NUM>.

In some embodiments, the top-emission type organic light emitting diode display substrate further includes a first via <NUM> extending through the inter-layer dielectric layer <NUM> and the gate insulating layer <NUM>. The drain electrode <NUM> is electrically connected to the active layer <NUM> through the first via <NUM>.

In some embodiments, the top-emission type organic light emitting diode display substrate further includes a second via <NUM> extending through the planarization layer <NUM> and the passivation layer <NUM>. The first electrode <NUM> is electrically connected to the drain electrode <NUM> through the second via <NUM>.

Various appropriate reflective conductive materials may be used for making the drain electrode <NUM>. Examples of appropriate reflective conductive materials include reflective conductive materials having a relatively low reflectivity. Optionally, the drain electrode <NUM> is made of a low-reflectivity metal such as molybdenum and nickel. Having a drain electrode <NUM> made of a reflective conductive material having a relatively low reflectivity further reduces microcavity effects in the top-emission type organic light emitting diode display substrate. Optionally, the drain electrode <NUM> includes a plurality of sub-layers laminated together. In one example, the drain electrode <NUM> is include a titanium/aluminum/titanium three-layer structure. As used herein, the term "low-reflectivity" refers to a layer or a material that reflects no more than approximately <NUM> percent (e.g., no more than approximately <NUM> percent, no more than approximately <NUM> percent, no more than approximately <NUM> percent, no more than approximately <NUM> percent, and no more than approximately <NUM> percent) of light in the visible wavelength range.

Various appropriate conductive materials may be used for making the first electrode <NUM>. Examples of appropriate conductive materials include substantially transparent conductive materials such as a metal oxide material. Optionally, the first electrode <NUM> is made of indium tin oxide. By having the first electrode <NUM> made of a substantially transparent conductive material, the reflectivity of the first electrode <NUM> is much reduced, further reducing microcavity effects in the top-emission type organic light emitting diode display substrate.

Various appropriate insulating materials may be used for making the planarization layer <NUM>. Examples of appropriate insulating materials include insulating materials having a relatively low refractive index, e.g., insulating polymer materials having a relatively low refractive index. Optionally, the planarization layer <NUM> is made of polydimethylsiloxane (PDMS). By having the planarization layer <NUM> made of an insulating material having a relatively low refractive index, light reflection by the drain electrode <NUM> can be further reduced, minimizing microcavity effects in the top-emission type organic light emitting diode display substrate.

Various appropriate insulating materials may be used for making the passivation layer <NUM>. Examples of appropriate insulating materials include silicon nitride (SiNx).

Various appropriate conductive materials may be used for making the second electrode <NUM>. Examples of appropriate conductive materials include substantially transparent metal materials. Optionally, the second electrode <NUM> is made of magnesium:silver alloy (Mg:Ag). Optionally, the second electrode <NUM> is made of nano-silver. By having a substantially transparent metallic second electrode <NUM>, the fabrication process of the display substrate obviates the need of sputtering a substantially transparent metal oxide material for making the second electrode <NUM>. The potential damages to the organic layer caused by the sputtering process can be entirely avoided, thereby simplifying the fabrication process and enhancing the quality and life time of the product. Optionally, the second electrode <NUM> is formed by a vapor deposition process, e.g., a plasma-enhanced chemical vapor deposition process.

Optionally, the buffer layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the buffer layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the active layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the active layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the gate insulating layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the gate insulating layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the gate electrode <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the gate electrode <NUM> has a thickness of approximately <NUM>Å.

Optionally, the inter-layer dielectric layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the inter-layer dielectric layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the drain electrode <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the drain electrode <NUM> has a thickness of approximately <NUM>Å.

Optionally, the planarization layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the planarization layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the passivation layer <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the passivation layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the first electrode <NUM> has a thickness in a range of approximately <NUM>Å to approximately <NUM>Å. Optionally, the first electrode <NUM> has a thickness of approximately <NUM>Å.

Optionally, the first hole injection layer <NUM> has a thickness of approximately <NUM>Å, the second hole injection layer <NUM> has a thickness of approximately <NUM>Å, the red light emitting layer <NUM> has a thickness of approximately <NUM>Å, the green light emitting layer <NUM> has a thickness of approximately <NUM>Å, the first electron transport layer <NUM> has a thickness of approximately <NUM>Å, the first charge generating layer <NUM> has a thickness of approximately <NUM>Å, the third hole injection layer <NUM> has a thickness of approximately <NUM>Å, the hole transport layer <NUM> has a thickness of approximately <NUM>Å, the blue light emitting layer <NUM> has a thickness of approximately <NUM>Å, the second electron transport layer <NUM> has a thickness of approximately <NUM>Å, and the second charge generating layer <NUM> has a thickness of approximately <NUM>Å.

Optionally, the planarization layer <NUM> has a refractive index of approximately <NUM>. Optionally, the passivation layer <NUM> has a refractive index of approximately <NUM>. Optionally, the first electrode <NUM> has a refractive index of approximately <NUM>. Optionally, each of the sub-layers in the organic layer <NUM> (e.g., the organic light emitting layer 11a, the first hole injection layer <NUM>, the green light emitting layer <NUM>, etc.) has a refractive index of approximately <NUM>.

Optionally, the planarization layer <NUM> includes a plurality of sub-layers. Optionally, each of the plurality of sub-layers of the planarization layer <NUM> has a different refractive index. Optionally, the refractive indexes of the plurality of sub-layers of the planarization layer <NUM> change in a step-wise fashion or in a linear fashion along the depth of the planarization layer <NUM>. Optionally, the refractive indexes of the plurality of sub-layers of the planarization layer <NUM> decrease (e.g., in a step-wise fashion or in a linear fashion) along a thickness direction away from the base substrate <NUM>. Similarly, in some embodiments, any of the other layers in the present display substrate may include a plurality of sub-layers, and the refractive indexes of the plurality of sub-layers may change in a step-wise fashion or in a linear fashion along the depth of the particular layer. Optionally, the refractive indexes of the plurality of sub-layers decrease (e.g., in a step-wise fashion or in a linear fashion) along a thickness direction away from the base substrate <NUM>.

Referring to <FIG>, the drain electrode <NUM> and the second electrode <NUM> according to the present invention form a microcavity structure M. As used herein, the term "microcavity" refers to a resonant optical cavity in a solid-state light emitting device. According to the present invention the drain electrode <NUM> and the second electrode <NUM> constitute two reflective mirrors in the microcavity structure M. Optionally, the microcavity structure M has an optical distance substantially equal to a sum of optical path lengths of layers between the drain electrode <NUM> and the second electrode <NUM>. As used herein, the term "optical path length" refers to a value obtained by multiplying a refractive index n of a medium through which the measurement light travels by a distance the measurement light travels through the medium having the refractive index n, i.e., the optical path length is equal to a distance the measurement light would travel through a vacuum during the time it takes for the measurement light to travel through the medium having the refractive index n.

According to the present invention the optical distance of the microcavity structure M is a non-integer multiple of 2πλ, λ is a wavelength of light emitted from the organic light emitting layer. By having the optical distance of the microcavity structure M to be a non-integer multiple of 2πλ, the microcavity effects of the microcavity structure M can be effectively reduced.

In some embodiments, the optical distance of the microcavity structure M is substantially equal to a sum of optical path lengths of the passivation layer <NUM>, the planarization layer <NUM>, the organic layer <NUM>, and the first electrode <NUM>. Optionally, the optical distance of the microcavity structure M is substantially equal to DPLN8*NPLN8 + DPVX9*NPVX9 + DIT010*NITO10 + DHIL111*NHIL111 + DHIL112*NHIL112 + DREML113*NREML113 + DGEML114*NGEML114 + DETL115*NETL115 + DCGL116*NCGL116 + DHIL117*NHIL117 + DHTL118*NHTL118 + DBEML119*NBEML119 + DETL120*NETL120 + DCGL121*NCGL121. Optionally, the optical distance of the microcavity structure M is substantially equal to 20000Å*<NUM> + 1000Å*<NUM> + 1500Å*<NUM> + 50Å*<NUM> + 330Å*<NUM> + 100Å*<NUM> + <NUM>Å*<NUM> + 100Å*<NUM> + 200Å*<NUM> + 1100Å*<NUM> + 100Å*<NUM> + 250Å*<NUM> + 400Å*<NUM> + 1000Å*<NUM> = 41774Å, and substantially not equal to k*2πλ, wherein DPLN8 is the thickness of the planarization layer <NUM>; NPLN8 is the refractive index of the planarization layer <NUM>; DPVX9 is the thickness of the passivation layer <NUM>; NPVX9 is the refractive index of the passivation layer <NUM>; DIT010 is the thickness of the first electrode <NUM>; NITO10 is the refractive index of the first electrode <NUM>; DHIL111 is the thickness of the first hole injection layer <NUM>; NHIL111 is the refractive index of the first hole injection layer <NUM>; DHIL112 is the thickness of the second hole injection layer <NUM>; NHIL112 is the refractive index of the second hole injection layer <NUM>; DREML113 is the thickness of the red light emitting layer <NUM>; NREML113 is the refractive index of the red light emitting layer <NUM>; DGEML114 is the thickness of the green light emitting layer <NUM>; NGEML114 is the refractive index of the green light emitting layer <NUM>; DETL115 is the thickness of the first electron transport layer <NUM>; NETL115 is the refractive index of the first electron transport layer <NUM>; DCGL116 is the thickness of the first charge generating layer <NUM>; NCGL116 is the refractive index of the first charge generating layer <NUM>; DHIL117 is the thickness of the third hole injection layer <NUM>; NHIL117 is the refractive index of the third hole injection layer <NUM>; DHTL118 is the thickness of the hole transport layer <NUM>; NHTL118 is the refractive index of the hole transport layer <NUM>; DBEML119 is the thickness of the blue light emitting layer <NUM>; NBEML119 is the refractive index of the blue light emitting layer <NUM>; DETL120 is the thickness of the second electron transport layer <NUM>; NETL120 is the refractive index of the second electron transport layer <NUM>; DCGL121 is the thickness of the second charge generating layer <NUM>; NCGL121 is the refractive index of the second charge generating layer <NUM>; k is a positive integer, and λ is a wavelength of light emitted from the organic light emitting layer.

The planarization layer <NUM> includes a plurality of sub-layers. The optical path length of the planarization layer <NUM> is substantially equal to the sum of optical path lengths of the plurality of sub-layers of the planarization layer <NUM>. Similarly, in some embodiments, any of the other layers in the present display substrate may include a plurality of sub-layers, and the optical path length of a particular layer is substantially equal to the sum of optical path lengths of the plurality of sub-layers of that particular layer.

In the present display substrate, the optical distance of the microcavity structure M is designed to be a non-integer multiple of 2πλ, λ is a wavelength of light emitted from the organic light emitting layer. For example, the optical distance of the microcavity structure M may be set by choosing a thickness and a refractive index for each layer between the drain electrode <NUM> and the second electrode <NUM>. By having this design, the microcavity effects of the microcavity structure M can be effectively reduced.

<FIG> is a comparison between emission spectra of a conventional organic light emitting diode display substrate and a top-emission type organic light emitting diode display substrate in some embodiments according to the present disclosure. Referring to <FIG>, the emission spectrum of the conventional organic light emitting diode display substrate is denoted as "A", and the emission spectrum of the present top-emission type organic light emitting diode display substrate is denoted as "B". The present top-emission type organic light emitting diode display substrate has reduced microcavity effects as compared to the conventional organic light emitting diode display substrate. As shown in <FIG>, the present top-emission type organic light emitting diode display substrate has a broader emission spectrum as compared to that of the conventional organic light emitting diode display substrate. Thus, the present top-emission type organic light emitting diode display substrate achieves a full spectrum emission of light.

<FIG> is a schematic diagram illustrating the structure of a top-emission type organic light emitting diode display substrate in some embodiments according to the present disclosure. Referring to <FIG>, the top-emission type organic light emitting diode display substrate in some embodiments does not include a passivation layer (as compared to that in <FIG>). The planarization layer <NUM> is between the first electrode <NUM> and the drain electrode <NUM>. Specifically, the planarization layer <NUM> is on a side of the drain electrode <NUM> distal to the base substrate <NUM>, and the first electrode <NUM> is on a side of the planarization layer <NUM> distal to the drain electrode <NUM>. The second via <NUM> extends through the planarization layer <NUM>, and the first electrode <NUM> is electrically connected to the drain electrode <NUM> through the second via <NUM>.

The optical distance of the microcavity structure M is substantially equal to a sum of optical path lengths of the planarization layer <NUM>, the organic layer <NUM>, and the first electrode <NUM>.

In some embodiments not forming part of the present display substrate, a microcavity is not formed between the first electrode <NUM> and the second electrode <NUM>, but between the drain electrode <NUM> and the second electrode <NUM>. The first electrode <NUM> is disposed at a position corresponding to the drain electrode <NUM>. The width of the drain electrode <NUM> is equal to or greater than that of the first electrode <NUM>. The microcavity structure in the present display substrate has a much greater optical distance as compared to that in the conventional display substrate, resulting in much reduced microcavity effects. The present display substrate achieves a full spectrum emission of light and enhanced light emission properties. The first electrode <NUM> is made of a substantially transparent conductive material such as a substantially transparent metal oxide, reducing reflectivity of the first electrode <NUM> and microcavity effects. The second electrode <NUM> is made of a metal material, obviating a sputtering process for depositing electrode material for forming the second electrode <NUM>, thus avoiding any damages to the organic layer <NUM> accompanied by the sputtering process. A simplified fabricating process and enhanced product quality and life time can be achieved. By choosing the thicknesses and refractive indexes for each of the layers between the drain electrode <NUM> and the second electrode <NUM>, the optical distance can be set to be a non-integer multiple of 2πλ, further reducing microcavity effects in the present display substrate.

In another aspect, the present disclosure provides a top-emission type organic light emitting diode display apparatus having a top-emission type organic light emitting diode display substrate described herein. Optionally, the top-emission type organic light emitting diode display substrate is a white light emitting display substrate. Optionally, the top-emission type organic light emitting diode display apparatus further includes a color filter substrate facing the light emitting side of the top-emission type organic light emitting diode display apparatus. Optionally, the top-emission type organic light emitting diode display apparatus includes an encapsulating layer on the light emitting side of the top-emission type organic light emitting diode display substrate, and the color filter substrate is on a side of the encapsulating layer distal to the top-emission type organic light emitting diode display substrate.

In another aspect, the present disclosure provides a method of forming a top-emission type organic light emitting diode display substrate in accordance with claim <NUM>. Optionally, the step of forming the organic light emitting diode includes forming a first electrode on a side of the drain electrode distal to the base substrate, the first electrode is formed using a substantially transparent conductive material and formed to be electrically connected to the drain electrode; forming an organic layer on a side of the first electrode distal to the drain electrode, the organic layer including an organic light emitting layer; and forming a second electrode on a side of the organic layer distal to the first electrode. Optionally, the top-emission type organic light emitting diode display substrate is formed to emit light substantially along a direction from the first electrode to the second electrode.

Optionally, the drain electrode and the organic light emitting layer are formed so that an orthographic projection of the drain electrode on the base substrate substantially covers that of a light emitting region of the organic light emitting layer. Optionally, the drain electrode and the organic light emitting layer are formed so that the orthographic projection of the drain electrode on the base substrate substantially overlaps with that of the light emitting region of the organic light emitting layer. Optionally, the drain electrode and the first electrode layer are formed so that the orthographic projection of the drain electrode on the base substrate substantially covers that of the first electrode layer. Optionally, the drain electrode and the first electrode layer are formed so that the orthographic projection of the drain electrode on the base substrate substantially overlaps with that of the first electrode layer.

The method further includes forming a planarization layer on a side of the drain electrode distal to the base substrate. Optionally, the method further includes forming a passivation layer on a side of the planarization layer distal to the drain electrode.

Claim 1:
A top-emission type organic light emitting diode display substrate having a plurality of subpixel areas in each of which the top-emission type organic light emitting diode display substrate comprises:
a base substrate (<NUM>);
a thin film transistor (<NUM>) on the base substrate (<NUM>) and comprising a drain electrode (<NUM>);
a planarization layer (<NUM>) on a side of the drain electrode (<NUM>) distal to the base substrate (<NUM>) ; an organic light emitting diode (<NUM>) on the planarization layer (<NUM>);
wherein the drain electrode (<NUM>) is a reflective electrode;
the organic light emitting diode (<NUM>) comprises:
a first electrode (<NUM>) on the planarization layer (<NUM>);
the first electrode (<NUM>) is a substantially transparent electrode and electrically connected to the drain electrode (<NUM>);
an organic layer (<NUM>) on a side of the first electrode (<NUM>) distal to the drain electrode (<NUM>), the organic layer (<NUM>) comprises an organic light emitting layer (11a); and
a second electrode (<NUM>) on a side of the organic layer (<NUM>) distal to the first electrode (<NUM>),
the second electrode (<NUM>) is a substantially transparent electrode;
the drain electrode (<NUM>) and the second electrode (<NUM>) form a microcavity structure (M);
the microcavity structure (M) has an optical distance substantially equal to a sum of optical path lengths of layers between the drain electrode (<NUM>) and the second electrode (<NUM>);
the optical distance is a non-integer multiple of 2πλ, λ is a wavelength of light emitted from the organic light emitting layer (11a);
the planarization layer (<NUM>) comprises a plurality of sub-layers; and the refractive indexes of the plurality of sub-layers of the planarization layer (<NUM>) decrease in a step-wise fashion along a thickness direction away from the base substrate (<NUM>).