# Organic Photoelectric Materials and Organic Photoelectric Devices Based on Smart Image Sensors

Authors: Gang Huang
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

With the development of the times in recent years, people’s requirements for vision are no longer limited to the original foundation. As the core of research in this field, organic electroluminescence has paid great attention to the research points in the application of organic optoelectronic materials and devices in the world. From the relevant scientific research results in recent years, for example, organic light-emitting diodes can be used in flat-panel displays and solid-state lighting, organic photovoltaic cells can be used as a clean and renewable energy source to effectively alleviate the current energy needs of society, and organic storage, sensors, and so on show great promise for application. It can be seen that the research of organic optoelectronic materials and their devices will be the core hot spot of future new energy research. In the past, traditional organic optoelectronic materials are updated through the regulation strategy of covalent modification of the molecular structure. In recent years, new effective methods have been obtained to regulate the properties of excited states through physical stimulation (such as mechanical force, temperature, electric field, and magnetic field). The type of research experiment in this paper is based on the current hot smart image sensor, with the addition of organic complexes of mononuclear metal platinum and iridium metal and the organic optoelectronic device in the form of host and guest doping. The experimental results show that using PVK without energy transfer, polyvinyl carbazole (PVK) had been widely used as blue luminescent material and hole transport layer in electroluminescent device research. Simple mononuclear platinum and iridium metal complexes cannot obtain white light. For OPV devices, by selecting the correct solvent to control the bulk heterojunction, it exhibits better photovoltaic performance. Solvents play an important role in phase separation. In organic solar cells (OPV) consisting of an electron donor (D) and an acceptor (A), optimizing the D-A interface produces efficient charge separation, effectively separating excitons at the D-A interface and forming continuous electron and hole transport channels, and effective charge transport between electrodes plays a positive role.


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## Body

## 1. Introduction

### 1.1. Background

Under the current conditions of rapid economic and social development, the application prospects of organic optoelectronic materials are very attractive. Because there are effective solutions to the problems of luminous brightness, efficiency, and lifespan at present, that is, through the application of light-emitting diodes, electrical energy can be efficiently converted into light energy, which has a wide range of uses in modern society, such as lighting, flat-panel displays, and medical devices. It will be widely used in civil and military in the future. First of all, high-efficiency white light can be used in the field of lighting. Various forms of lamps and lanterns bring new visual impact. Colorful lights can be used in stage lighting design; at the same time, they can also be used to make large-screen full-color high-definition flat-panel displays. It can also be used to make e-books. The textbooks will no longer be heavy and thick paper books, but thin and light e-books. The soft light source will make reading more colorful. In the military, it can be used for display instrument panels of operating platforms such as tanks and airplanes. Compared with organic optoelectronic materials, which have the characteristics of low preparation cost, small workload during processing, and convenient operation, organic optoelectronic devices have low cost, lightweight, easy design, and synthesis of materials and can be made into large-area displays, flexible, and foldable displays [1]. The screen, because of its simple preparation process, etc., can attract more attention from all aspects. In recent years, optoelectronic devices have been developed with their different functions. What is beneficial to modern life is electronic equipment that can be used to retrieve images and smart cards, as well as memory cards and sensors with excellent applications [2]. In the case of organic optoelectronic devices, the interface has a significant impact on the performance and service life of the device. Image sensors use the photoelectric conversion function of photoelectric devices. It converts the light image on the light-sensitive surface into an electrical signal with a corresponding proportional relationship with the light image. Image sensors are widely used in digital cameras and other imaging devices. Light-emitting diode is a common light-emitting device, in the field of electronic display, and is one of the commonly used materials, the study of which can well enhance the efficacy of the response and provide a wider viewing angle.


### 1.2. Significance

In recent years, research on organic electroluminescent devices and photovoltaic equipment and accessories has continued. Related scientific research results are still emerging. It is believed that in the next few years, organic electroluminescent devices will move from the laboratory to the market, and photovoltaic equipment and organic equipment will also be improved. Related research content has developed an organic photovoltaic device with an efficiency of 8.22%. The efficiency of organic solar cells exceeds 15%, which will be the next goal. For some time to come, organic optoelectronic materials and devices will still be the focus of new energy research.


### 1.3. Related Work

For related research, many scholars have laid the foundation for this empirical research. In sensor research, Hasani A investigated the latest developments in the application of two-dimensional materials and MOF in taste sensing applications. From the review, they concluded that these materials will become promising candidates for taste applications, leading to the development of the food industry [3]. Xia et al. demonstrated the most comprehensive performance and performance of organic ferroelectric polymer materials and their composites, as well as the improvement of organic-inorganic hybrid ferroelectric materials. Finally, the future growth rate of ferroelectric materials is predicted to some extent [4]. In the use of wireless sensor networks (WSNs) to achieve accurate perception of agricultural planting information, Fen et al. proposed a hybrid WSN node based on smartphones. Nodes can support traditional central agricultural management functions through terminal/host configuration. Tourists and farmers can also directly visit the node and use on-site information services. The design of the node hardware and the corresponding smartphone application program is discussed, and the test results in the BTH Tourism Farm are given [5]. Based on sensor research and innovation, Andika et al. demonstrated a new nanoporous structure of aluminum 1,8,15,22-tetra29H, 31H chlorinated phthalocyanine (AlPcCl), which is prepared by a template-assisted method for humidity sensor. The nanoporous sensing layer was prepared by wetting the anodic aluminum oxide template with a solution. AlPcCl solutions of different concentrations are spin cast on the template at different speeds. Both capacitance and resistance responses are measured as a function of different relative humidity levels. The sensor shows a wide operating relative humidity range and responds at a relatively low humidity level. The morphological changes were studied by field emission scanning electron microscopy. The sensor shows a wide operating relative humidity range. The sensor shows better performance through improved sensing parameters, highlighting the unique advantages of low-molecular nanostructured sensing layers for humidity sensors [6]. Choi et al. proposed a pixel aperture technology in complementary metal oxide semiconductor (CMOS) image sensors for 3D imaging. In traditional camera systems, the aperture is located between the object and the CMOS image sensor (CIS); this type of image sensor consists of an array of pixels with red, green, and blue (RGB) Bayer pattern color filters [7]. Liu et al. introduced the evaluation of the optical and electrical characteristics of ultrathin body and buried oxide (UTBB) MOSFETs with different structures. UTBB MOSFET can realize photoelectric conversion by integrating a doped well or photodiode under the BOX. For lightly doped wells, well-UTBB (W-UTBB) image sensors are more sensitive to light. On the other hand, the photodiode-UTBB (PD-UTBB) image sensor has a larger full well capacity. The effects of good doping concentration and interface traps at the BOX/well on the optoelectronic properties of the two devices have been studied. A good doping concentration has a great influence on the photosensitivity of W-UTBB. Interface traps will increase the dark current of W-UTBB and reduce the internal quantum efficiency (IQE) of PD-UTBB [8]. In the research on organic optoelectronic materials, Yoon’s multi-pattern nanostructures prepared by synergistically combining block copolymer lithography and nanoimprint lithography have been used as back reflectors to enhance light absorption in organic optoelectronic devices. Due to efficient light scattering and plasma effects, multi-patterned electrodes significantly improve the performance of organic photovoltaics and phototransistors and expand their practical application range. The abovementioned scholars all need an over-professional and in-depth knowledge base for related research, the operation process is complicated, and there is a certain degree of danger.


### 1.4. Innovation

This research mainly carried out optimization and performance research on two aspects of doped organic electroluminescent white light devices and organic photovoltaic devices. (1) In the experiment, the mononuclear iridium (platinum) ring metal complex with nonplanar structure was mainly studied systematically [9], and the doped electroporation was designed with PVK as the main body and platinum and iridium metal complexes as the guest material, and studied the optoelectronic properties of this series of OLEDs. (2) The organic photovoltaic device is mainly based on the PC61BM acceptor and P3HT [10]. In this paper, three materials, P3HT (polymer of 3-hexylthiophene), PFO-ThPz-Tpa copolymer, and PFO-FCz-DBT30 copolymer, are proposed as guest materials to prepare solar cells, and they are optimized in the preparation process to further investigate the performance of photovoltaic devices [11].


## 1.1. Background

Under the current conditions of rapid economic and social development, the application prospects of organic optoelectronic materials are very attractive. Because there are effective solutions to the problems of luminous brightness, efficiency, and lifespan at present, that is, through the application of light-emitting diodes, electrical energy can be efficiently converted into light energy, which has a wide range of uses in modern society, such as lighting, flat-panel displays, and medical devices. It will be widely used in civil and military in the future. First of all, high-efficiency white light can be used in the field of lighting. Various forms of lamps and lanterns bring new visual impact. Colorful lights can be used in stage lighting design; at the same time, they can also be used to make large-screen full-color high-definition flat-panel displays. It can also be used to make e-books. The textbooks will no longer be heavy and thick paper books, but thin and light e-books. The soft light source will make reading more colorful. In the military, it can be used for display instrument panels of operating platforms such as tanks and airplanes. Compared with organic optoelectronic materials, which have the characteristics of low preparation cost, small workload during processing, and convenient operation, organic optoelectronic devices have low cost, lightweight, easy design, and synthesis of materials and can be made into large-area displays, flexible, and foldable displays [1]. The screen, because of its simple preparation process, etc., can attract more attention from all aspects. In recent years, optoelectronic devices have been developed with their different functions. What is beneficial to modern life is electronic equipment that can be used to retrieve images and smart cards, as well as memory cards and sensors with excellent applications [2]. In the case of organic optoelectronic devices, the interface has a significant impact on the performance and service life of the device. Image sensors use the photoelectric conversion function of photoelectric devices. It converts the light image on the light-sensitive surface into an electrical signal with a corresponding proportional relationship with the light image. Image sensors are widely used in digital cameras and other imaging devices. Light-emitting diode is a common light-emitting device, in the field of electronic display, and is one of the commonly used materials, the study of which can well enhance the efficacy of the response and provide a wider viewing angle.


## 1.2. Significance

In recent years, research on organic electroluminescent devices and photovoltaic equipment and accessories has continued. Related scientific research results are still emerging. It is believed that in the next few years, organic electroluminescent devices will move from the laboratory to the market, and photovoltaic equipment and organic equipment will also be improved. Related research content has developed an organic photovoltaic device with an efficiency of 8.22%. The efficiency of organic solar cells exceeds 15%, which will be the next goal. For some time to come, organic optoelectronic materials and devices will still be the focus of new energy research.


## 1.3. Related Work

For related research, many scholars have laid the foundation for this empirical research. In sensor research, Hasani A investigated the latest developments in the application of two-dimensional materials and MOF in taste sensing applications. From the review, they concluded that these materials will become promising candidates for taste applications, leading to the development of the food industry [3]. Xia et al. demonstrated the most comprehensive performance and performance of organic ferroelectric polymer materials and their composites, as well as the improvement of organic-inorganic hybrid ferroelectric materials. Finally, the future growth rate of ferroelectric materials is predicted to some extent [4]. In the use of wireless sensor networks (WSNs) to achieve accurate perception of agricultural planting information, Fen et al. proposed a hybrid WSN node based on smartphones. Nodes can support traditional central agricultural management functions through terminal/host configuration. Tourists and farmers can also directly visit the node and use on-site information services. The design of the node hardware and the corresponding smartphone application program is discussed, and the test results in the BTH Tourism Farm are given [5]. Based on sensor research and innovation, Andika et al. demonstrated a new nanoporous structure of aluminum 1,8,15,22-tetra29H, 31H chlorinated phthalocyanine (AlPcCl), which is prepared by a template-assisted method for humidity sensor. The nanoporous sensing layer was prepared by wetting the anodic aluminum oxide template with a solution. AlPcCl solutions of different concentrations are spin cast on the template at different speeds. Both capacitance and resistance responses are measured as a function of different relative humidity levels. The sensor shows a wide operating relative humidity range and responds at a relatively low humidity level. The morphological changes were studied by field emission scanning electron microscopy. The sensor shows a wide operating relative humidity range. The sensor shows better performance through improved sensing parameters, highlighting the unique advantages of low-molecular nanostructured sensing layers for humidity sensors [6]. Choi et al. proposed a pixel aperture technology in complementary metal oxide semiconductor (CMOS) image sensors for 3D imaging. In traditional camera systems, the aperture is located between the object and the CMOS image sensor (CIS); this type of image sensor consists of an array of pixels with red, green, and blue (RGB) Bayer pattern color filters [7]. Liu et al. introduced the evaluation of the optical and electrical characteristics of ultrathin body and buried oxide (UTBB) MOSFETs with different structures. UTBB MOSFET can realize photoelectric conversion by integrating a doped well or photodiode under the BOX. For lightly doped wells, well-UTBB (W-UTBB) image sensors are more sensitive to light. On the other hand, the photodiode-UTBB (PD-UTBB) image sensor has a larger full well capacity. The effects of good doping concentration and interface traps at the BOX/well on the optoelectronic properties of the two devices have been studied. A good doping concentration has a great influence on the photosensitivity of W-UTBB. Interface traps will increase the dark current of W-UTBB and reduce the internal quantum efficiency (IQE) of PD-UTBB [8]. In the research on organic optoelectronic materials, Yoon’s multi-pattern nanostructures prepared by synergistically combining block copolymer lithography and nanoimprint lithography have been used as back reflectors to enhance light absorption in organic optoelectronic devices. Due to efficient light scattering and plasma effects, multi-patterned electrodes significantly improve the performance of organic photovoltaics and phototransistors and expand their practical application range. The abovementioned scholars all need an over-professional and in-depth knowledge base for related research, the operation process is complicated, and there is a certain degree of danger.


## 1.4. Innovation

This research mainly carried out optimization and performance research on two aspects of doped organic electroluminescent white light devices and organic photovoltaic devices. (1) In the experiment, the mononuclear iridium (platinum) ring metal complex with nonplanar structure was mainly studied systematically [9], and the doped electroporation was designed with PVK as the main body and platinum and iridium metal complexes as the guest material, and studied the optoelectronic properties of this series of OLEDs. (2) The organic photovoltaic device is mainly based on the PC61BM acceptor and P3HT [10]. In this paper, three materials, P3HT (polymer of 3-hexylthiophene), PFO-ThPz-Tpa copolymer, and PFO-FCz-DBT30 copolymer, are proposed as guest materials to prepare solar cells, and they are optimized in the preparation process to further investigate the performance of photovoltaic devices [11].


## 2. Organic Photoelectric Materials Based on Smart Image Sensors

### 2.1. The Development Status of Organic Optoelectronic Materials

In 1963, American scholars first discovered the luminescence phenomenon of organic materials [12]: under 400 V DC voltage, single-crystal anthracene will emit weak fluorescence. Although the turn-on voltage and efficiency were not good at that time, the discovery made humans realize for the first time that organic materials can also emit light, laying the foundation for future research on organic electroluminescence. Until 1987, it was reported that 8-hydroxyquinoline aluminum (Alq3) [13], an organic small molecule light-emitting material, was prepared by vacuum evaporation method to prepare a sandwich structure of green fluorescent OLED (organic electroluminescent display) devices [14]. This is also the world’s first OLED device, device structure, and molecule. The structure is shown in Figure 1. The turn-on voltage of the device is less than 10 V, and the brightness is more than 1000 cd/m2. This research result has attracted worldwide attention as soon as it was reported. People began to pay attention to the potential applications of organic materials in the display field [15, 16]. Organic optoelectronic materials are mainly used in organic solar cells, organic light-emitting diodes, and OLEDs and other displays. Due to the rapid development of the electronic industry, many photoelectric display panel companies need organic optoelectronic materials. Research has gradually stepped onto the stage.Figure 1
Fluorescent OLED and luminescent material Alq3 prepared by Deng Qingyun and others.After years of development, some unique advantages of OLED [17] have been gradually discovered by mankind: no backlight, ultra-fast response speed, wide viewing angle, wide color gamut, flexible and bendable, etc. [18]. Compared with traditional liquid crystal display technology, OLED can better meet human visual requirements [19]. In addition, OLED is also simpler and lower in manufacturing cost than LCD (liquid crystal display) in terms of process, so OLED is also known as the third-generation display technology after LCD. At present, OLED has been commercialized in large-size display screens, small- and medium-size mobile phone screens, car display screens, etc., and has formed a rivalry with LCDs in the market, and the prospects are promising [20].


### 2.2. Working Principle Based on Smart Image Sensor

Image sensors are widely used in imaging devices such as digital cameras. Image sensors in the past used analog signals [21, 22]. The rapid development and progress of image sensors have made it possible to be used in space detection. According to different photodetectors used, image sensors can be divided into grating type and photodiode type [23]. Because organic light-emitting diodes are relatively lighter, thinner, and more flexible, the production process is easier. Therefore, it is analyzed in this paper. Analyzing the photodiode, it is found that when the electric field strength in the space charge region becomes larger, it is more likely to produce drift motion; i.e., the minority carriers in the P and N regions will make directional motion. The depletion region will remain stable when the diffusive motion and drift motion reach equilibrium; it is found that when the diffusion motion and drift motion reach equilibrium, the depletion region will remain stable [24], as shown in Figure 2. At this point, the PN junction is in thermal equilibrium. According to the theory of semiconductor physics, the height of the space charge region, which is the barrier region, is QV0, and the width of the depletion region, W, and the PN junction capacitance, Dc, are expressed as follows:(1)QV0=KtlnN0N1N12.Figure 2
PN combination at zero offset position.TheQV0 in the formula represents the height of the barrier, and its content shows that it is related to the doping concentration.(2)W=2δV0−VqN1+N0N12.Formula (2) shows that the V voltage can affect the width of the junction region, and it also shows that W will become larger if it is a forward bias [25].Considering the sudden change in capacitance based on junction energy:(3)Dc=aQδ2⋅N1N0N1+N0⋅1V0−V.It can be seen from (3) that the capacitance Dc is related to the voltage. The specific performance is Dc when forward bias will become larger; otherwise, it will be reduced.In the above formula,K=1.38×10−23J•k; t represents temperature. A represents the cross-sectional area of junction energy; δ is the electrical constant of the semiconductor. A voltage is applied to the PN junction under the condition of thermal equilibrium:(4)Ld=L0BQv/kt−L0.L0fQV/kt expresses the forward current flowing from the P area to the N area. When V=0, it is in a balanced state. L0 represents that the reverse charge saturation current will grow with the increase in temperature. Therefore, current will be generated by the reverse bias voltage.If a negative resistance is added at this time,Hrs represents that the junction resistance of PN can be ignored. So, the resistance of the load HL can be expressed as follows:(5)Ll=Ld−Lg=L0BQv/kt−L0−Lg.When the photocurrentLg is proportional to the intensity of the incident light,(6)Lg=Es⋅S.The sensitivity of theES meter in the formula is as follows:(7)Ll=Ld−Lg=L0BQv/kt−L0−Es⋅S.When there is no load, in the formulaLl=0, the open-circuit voltage at this time is expressed as follows:(8)Vmn=ktQIn1+LgL0.InLg≫L0, it is generally expressed as follows:(9)Vmn≈ktQInLgL0≈ktQInEs⋅SL0.HL=0, when short circuit is expressed as follows:(10)LEm=Lg=Es⋅S.At this time, the short-circuit current is directly proportional to the intensity of the incident light, and a reverse bias voltage is usually applied to thePN junction. Since the reverse bias voltage is consistent with the direction of the electric field in the junction, the space charge region will become wider and the barrier height will change. When QV0 increases to QV1+Vr, the electric field strength in the space charge region becomes larger, and the photo-generated electron-hole pairs are more likely to drift, so the frequency response characteristics of the device can be improved [26].


### 2.3. Principles of Organic Optoelectronic Devices

Principle of Organic Light-Emitting Diode [27]: the structure of an organic light-emitting diode is shown in Figure 3. It is composed of a high-performance transparent indium tin oxide (ITO) anode, a light transmission layer, an electrical transmission layer, an organic light-emitting layer, and a working metal cathode [28].Figure 3
Organic light-emitting diode structure.The energy level arrangement of the organic material device is shown in Figure4. If a forward electric field is applied, under its influence, holes are injected into the transport layer through the ITO anode with high efficiency, and electrons are injected into the electron transport process through the metal cathode at low power. The electron pair is formed by the recombination of electrons, and the holes are fixed by decomposition, electroplating, quenching, and other methods and easily return from the excited state to the ground state [29].Figure 4
Energy level ranking of organic light-emitting diodes.Principle of Organic Photovoltaic Cells [30]: organic photovoltaic cells are usually composed of a transparent indium tin oxide (ITO) anode, an organic process, and a metal cathode [31]. The model is shown in Figure 5.Figure 5
Organic photovoltaic cell structure.Figure6 illustrates the principle of organic photovoltaic cells. When sunlight passes through the ITO electrode and reaches the organic active layer, the organic material in the active layer absorbs the energy of incident photons to form photo-generated electron pairs. Molecular van der Waals forces work together [32], and the excitation of electrons and incident photons restrain the occurrence of electron pairs [33]. Under the potential of the receptor interaction, the electron pair is separated into electrons and holes, and the electrons jump into the LUMO energy phase of the acceptor and transition to the HOMO energy phase of the free substance [34].Figure 6
Sorting of organic photovoltaic cells.


## 2.1. The Development Status of Organic Optoelectronic Materials

In 1963, American scholars first discovered the luminescence phenomenon of organic materials [12]: under 400 V DC voltage, single-crystal anthracene will emit weak fluorescence. Although the turn-on voltage and efficiency were not good at that time, the discovery made humans realize for the first time that organic materials can also emit light, laying the foundation for future research on organic electroluminescence. Until 1987, it was reported that 8-hydroxyquinoline aluminum (Alq3) [13], an organic small molecule light-emitting material, was prepared by vacuum evaporation method to prepare a sandwich structure of green fluorescent OLED (organic electroluminescent display) devices [14]. This is also the world’s first OLED device, device structure, and molecule. The structure is shown in Figure 1. The turn-on voltage of the device is less than 10 V, and the brightness is more than 1000 cd/m2. This research result has attracted worldwide attention as soon as it was reported. People began to pay attention to the potential applications of organic materials in the display field [15, 16]. Organic optoelectronic materials are mainly used in organic solar cells, organic light-emitting diodes, and OLEDs and other displays. Due to the rapid development of the electronic industry, many photoelectric display panel companies need organic optoelectronic materials. Research has gradually stepped onto the stage.Figure 1
Fluorescent OLED and luminescent material Alq3 prepared by Deng Qingyun and others.After years of development, some unique advantages of OLED [17] have been gradually discovered by mankind: no backlight, ultra-fast response speed, wide viewing angle, wide color gamut, flexible and bendable, etc. [18]. Compared with traditional liquid crystal display technology, OLED can better meet human visual requirements [19]. In addition, OLED is also simpler and lower in manufacturing cost than LCD (liquid crystal display) in terms of process, so OLED is also known as the third-generation display technology after LCD. At present, OLED has been commercialized in large-size display screens, small- and medium-size mobile phone screens, car display screens, etc., and has formed a rivalry with LCDs in the market, and the prospects are promising [20].


## 2.2. Working Principle Based on Smart Image Sensor

Image sensors are widely used in imaging devices such as digital cameras. Image sensors in the past used analog signals [21, 22]. The rapid development and progress of image sensors have made it possible to be used in space detection. According to different photodetectors used, image sensors can be divided into grating type and photodiode type [23]. Because organic light-emitting diodes are relatively lighter, thinner, and more flexible, the production process is easier. Therefore, it is analyzed in this paper. Analyzing the photodiode, it is found that when the electric field strength in the space charge region becomes larger, it is more likely to produce drift motion; i.e., the minority carriers in the P and N regions will make directional motion. The depletion region will remain stable when the diffusive motion and drift motion reach equilibrium; it is found that when the diffusion motion and drift motion reach equilibrium, the depletion region will remain stable [24], as shown in Figure 2. At this point, the PN junction is in thermal equilibrium. According to the theory of semiconductor physics, the height of the space charge region, which is the barrier region, is QV0, and the width of the depletion region, W, and the PN junction capacitance, Dc, are expressed as follows:(1)QV0=KtlnN0N1N12.Figure 2
PN combination at zero offset position.TheQV0 in the formula represents the height of the barrier, and its content shows that it is related to the doping concentration.(2)W=2δV0−VqN1+N0N12.Formula (2) shows that the V voltage can affect the width of the junction region, and it also shows that W will become larger if it is a forward bias [25].Considering the sudden change in capacitance based on junction energy:(3)Dc=aQδ2⋅N1N0N1+N0⋅1V0−V.It can be seen from (3) that the capacitance Dc is related to the voltage. The specific performance is Dc when forward bias will become larger; otherwise, it will be reduced.In the above formula,K=1.38×10−23J•k; t represents temperature. A represents the cross-sectional area of junction energy; δ is the electrical constant of the semiconductor. A voltage is applied to the PN junction under the condition of thermal equilibrium:(4)Ld=L0BQv/kt−L0.L0fQV/kt expresses the forward current flowing from the P area to the N area. When V=0, it is in a balanced state. L0 represents that the reverse charge saturation current will grow with the increase in temperature. Therefore, current will be generated by the reverse bias voltage.If a negative resistance is added at this time,Hrs represents that the junction resistance of PN can be ignored. So, the resistance of the load HL can be expressed as follows:(5)Ll=Ld−Lg=L0BQv/kt−L0−Lg.When the photocurrentLg is proportional to the intensity of the incident light,(6)Lg=Es⋅S.The sensitivity of theES meter in the formula is as follows:(7)Ll=Ld−Lg=L0BQv/kt−L0−Es⋅S.When there is no load, in the formulaLl=0, the open-circuit voltage at this time is expressed as follows:(8)Vmn=ktQIn1+LgL0.InLg≫L0, it is generally expressed as follows:(9)Vmn≈ktQInLgL0≈ktQInEs⋅SL0.HL=0, when short circuit is expressed as follows:(10)LEm=Lg=Es⋅S.At this time, the short-circuit current is directly proportional to the intensity of the incident light, and a reverse bias voltage is usually applied to thePN junction. Since the reverse bias voltage is consistent with the direction of the electric field in the junction, the space charge region will become wider and the barrier height will change. When QV0 increases to QV1+Vr, the electric field strength in the space charge region becomes larger, and the photo-generated electron-hole pairs are more likely to drift, so the frequency response characteristics of the device can be improved [26].


## 2.3. Principles of Organic Optoelectronic Devices

Principle of Organic Light-Emitting Diode [27]: the structure of an organic light-emitting diode is shown in Figure 3. It is composed of a high-performance transparent indium tin oxide (ITO) anode, a light transmission layer, an electrical transmission layer, an organic light-emitting layer, and a working metal cathode [28].Figure 3
Organic light-emitting diode structure.The energy level arrangement of the organic material device is shown in Figure4. If a forward electric field is applied, under its influence, holes are injected into the transport layer through the ITO anode with high efficiency, and electrons are injected into the electron transport process through the metal cathode at low power. The electron pair is formed by the recombination of electrons, and the holes are fixed by decomposition, electroplating, quenching, and other methods and easily return from the excited state to the ground state [29].Figure 4
Energy level ranking of organic light-emitting diodes.Principle of Organic Photovoltaic Cells [30]: organic photovoltaic cells are usually composed of a transparent indium tin oxide (ITO) anode, an organic process, and a metal cathode [31]. The model is shown in Figure 5.Figure 5
Organic photovoltaic cell structure.Figure6 illustrates the principle of organic photovoltaic cells. When sunlight passes through the ITO electrode and reaches the organic active layer, the organic material in the active layer absorbs the energy of incident photons to form photo-generated electron pairs. Molecular van der Waals forces work together [32], and the excitation of electrons and incident photons restrain the occurrence of electron pairs [33]. Under the potential of the receptor interaction, the electron pair is separated into electrons and holes, and the electrons jump into the LUMO energy phase of the acceptor and transition to the HOMO energy phase of the free substance [34].Figure 6
Sorting of organic photovoltaic cells.


## 3. Experimental Research on Organic Optoelectronic Devices Based on Metal-Organic Complexes

In this study, the phosphorescent material platinum-iridium metal-organic complex was doped into the host material, and the organic layer was completed by the suction sheet spin coating process, and the annealing temperature was 120°C. PVK has a strong hole transport ability. The electron transport material PBD(2-(4-biphenyl)-5-phenyl) is added to balance the injection of carriers, and the ratio of PVK to PBD is 7 : 3. The device structure is ITO/PEDOT:PSS (40 nm)/PVK-PBD:sample (75 nm)/LiF (0.5 nm)/Al (100 nm). In the experiment, the solvent is chlorobenzene (CB), and the mass ratio of the guest material to the PVK-PBD (wt%, 7 : 3) blend is 0.5%, 1%, 2%, 4%, and 8%.


### 3.1. OLEDs/OPV Device Manufacturing Process 1

Generally speaking, the preparation process of OLEDs/OPV devices includes the processing of ITO glass substrate, the preparation of organic functional layers, the preparation of cathode modified layers and metal cathodes, and the packaging and testing of devices. The following is a detailed introduction to the specific steps:(1)
The ITO glass resistance used in the ITO glass substrate processing experiment is 15 Ω. First, a glass knife is used to scratch a 15 × 60 mm2 glass substrate, and a layer of vacuum tape is stuck on the side where the ITO is deposited to ensure the tape. The edges are neat and there are no air bubbles, especially the edge part; otherwise, it will be corroded. A utility knife is used to scratch the 3 mm × 80 mm tape, the protruding part of the tape is stuck on the back to prevent the ITO at the edge from being corroded, then the ITO glass substrate is attached face-up, a layer of zinc powder in a Petri dish is spread and corroded with concentrated hydrochloric acid for 25∼30 s, the residue attached to the surface is quickly rinsed with a large amount of water, and finally the tape is removed; the substrate with neat edges is selected, and glass is used. The knife is divided into three equal sections and marked on the back for later use.(2)
Preparation of Organic Functional Layer at Present: there are two main methods for making OLED/OPV organic functional layer: small molecule materials generally use vacuum thermal evaporation; polymer materials use wet spin coating technology.(1)
Vacuum Thermal Evaporation: 20 small molecule thermal evaporation process is usually suitable to ensure that the vacuum degree is ∼10–4 Pa. The remaining gas after the vacuum may have a greater impact on the performance of the device.(2)
Wet Spin Coating Process: the wet spin coating process is mainly divided into the following categories: (a) suction sheet spin coating polymers are usually cross-linked, easily decomposed by heat, and are not easy to evaporate and deposit in the vacuum evaporation chamber. Therefore, in general, it is dissolved in a suitable solvent and deposited on the substrate through a suction sheet spin coating process. However, this limits the properties of the polymer to be soluble; the same solvent can no longer dissolve other polymers; otherwise, the solvent corrosion effect will appear. The production of flexible devices can be based on the principle of similar compatibility between solvents, using different solvents to dissolve different polymers and orderly spin coating to form a film. Although the thickness of the film produced by the spin coating process can be adjusted by controlling the concentration of the polymer in the solution, the spin coating rate, the spin coating temperature, etc., however, it is difficult to produce a film with a certain thickness and control the film thickness by monitoring the deposition process. In the semiconductor display industry, the spin coating process has been applied. However, the production of large-area flat-panel displays cannot be completed smoothly with the spin coating process. (b) Doctor blade process: in this process, the polymer is dissolved in a solvent and then coated on the substrate to form a certain thickness of film thickness, and the excess part is removed by precise doctor blade technology. Compared with the spin coating process, it is easier to make a relatively thick film, but the thickness of the film must not be less than 100 nm. This process is more common in the production of OLEDs. (c) Wet injection molding method: Yang et al. used inkjet printing technology to make OLEDs, which is a major advancement in the wet film manufacturing process. Compared with the wet sucking sheet spin coating process, wet injection molding technology can be used to make double-layer PLEDs, that is, adding organic layers that are not compatible with each other.


### 3.2. Characterization of Physical and Chemical Properties of Materials Made of Light-Emitting Devices Based on Mononuclear Platinum and Iridium Complexes

The thermal stability of mononuclear platinum and iridium metal-organic complexes P1 and P2 are calibrated, as shown in Figure7. Under the protection of nitrogen, the thermal weight loss of the two mononuclear complexes was measured at a temperature program rate of 20°C/min. The two complexes P1 and P2 have good thermal stability, and the temperature (Td) at 5% mass loss is 307°C and 292°C, respectively.Figure 7
Molecular structures of P1 and P2 complexes.The UV-visible absorption spectra of the two mononuclear metal complexes P1 and P2 in CH2Cl2 (10–5 M) are shown in Figure8, and the relevant parameters are shown in Table 3.1. P1 exhibits three absorption peaks with different intensities near 240, 335, and 353 nm. P2 exhibits two weak absorption peaks with different intensities in the 260 nm and 350–450 nm regions. Among them, 240 nm and 260 nm are the π − π∗ transition absorption of platinum-iridium mononuclear metal, the absorption peak at 350∼450 nm is the transition absorption from the metal to the ligand, and the absorption of P1 at 330 nm and 350 nm the peak is attributed to the transition absorption of MLCT.Figure 8
UV-visible light absorption spectrum of metal complexes P1 and P2.Figure9 shows that in CH2Cl2, the complexes P1 and P2 have strong emission peaks near 475 nm and 497 nm. The emission peak around 475 nm can be attributed to the 1MLCT transition emission, and the emission around 497 nm can be attributed to the 3MLCT transition emission. At the same time, we studied the electrochemical properties of the two materials. The HOMO and LUMO energy levels of the material are obtained by the following empirical formula:(11)HLUMO=−Hred+4.38Ev,HLUMO=−H0x+4.38Ev,Hg=−HLUMO+HHOMOEv.Figure 9
PL spectrum of metal complexes P1 and P2 in CH2CI2.The LUMO and HOMO energy levels of P1 areELUMO=3.46Ev and ELUMO=6.63Ev, respectively; the LUMO and HOMO energy levels of P2 are ELUMO=3.2Ev and ELUMO=5.62Ev, respectively.


### 3.3. Characterization of Electroluminescence Performance of Light-Emitting Devices Based on Mononuclear Platinum and Iridium Complexes

The electroluminescence spectrum of the mononuclear platinum complex P1 device at a voltage of 8 V is shown in Figure10. The electroluminescence emission peak of PVK + PBD undoped metal complex device is shown in Figure 10.Figure 10
EL spectrum of metal complexes.It can be seen from Figure10that when the doping ratio is 1%, the EL spectrum presents three peaks: 450nm, 500nm, and 650nm. The peak at 431 nm is attributed to the emission peak of PVK. Starting from the doping concentration of 2%, as the doping ratio increases, the luminescence intensity of PVK at 431 nm gradually decreases, indicating that the concentration increases and the energy transfer efficiency between PVK and P2 gradually increases, which inhibits the luminescence of PVK. At the same time, the increase in the doping concentration also increases the proportion of the metal complexes directly capturing the carrier emission, and the increase in the concentration also causes the complexes to produce exciplex emission, which changes the spectrum.When P1: (PVK + PBD) doping concentration is 0.5%, the spectra under different driving voltages are shown in Figure11. With the increase in the voltage, there is basically no change in the position of the emission peak at 431 nm, but when the voltage is increased to 12 V, the emission intensity of PVK decreases and the excimer emission between the complexes increases. It shows that this luminescence should be related to the environment in which the excited state P1 molecule is located. This is consistent with the phenomenon described in articles reported in the literature. As the voltage increases, the number of carriers increases, the number of potential wells formed by the guest material increases, the number of carriers directly trapped increases, and the luminescence intensity increases, making the luminescence of PVK relatively weak.Figure 11
1EL spectrum under different voltages.The EL spectrum under different voltages is shown in Figure11. The comparison of experimental results shows that when the doping ratio is 1%, the EL spectrum shows three peaks: 431 nm, 476 nm, and 530 nm. The emission peak of P2 has many similarities with P1. The emission peak of PVK is at 431 nm, the emission peak of P2 itself is at 476 nm, and the emission peak at 530 nm is derived from the emission of the excimer between P2 molecules (excimer emission). Starting from the doping concentration of 2%, as the doping ratio increases, the luminescence intensity of PVK at 431 nm gradually decreases, indicating that the concentration increases and the energy transfer efficiency between PVK and P2 gradually increases, which inhibits the luminescence of PVK. At the same time, it can be seen that the emission intensity at 476 nm of P2 gradually decreases, and the emission intensity at 530 nm gradually increases. The decrease in emission intensity at 476 nm may be due to the absorption effect of the complex itself. The increase in luminescence intensity at 530 nm may be due to the increase in doping ratio, and there is interaction between molecules, the probability of transition between molecules increases, and the formation of excimer luminescence.Although the ignition voltage of platinum and iridium mononuclear complexes is relatively low, which is basically between 7 V and 9 V, the white light region luminescence spectrum is obtained, but pure white light is not obtained.


## 3.1. OLEDs/OPV Device Manufacturing Process 1

Generally speaking, the preparation process of OLEDs/OPV devices includes the processing of ITO glass substrate, the preparation of organic functional layers, the preparation of cathode modified layers and metal cathodes, and the packaging and testing of devices. The following is a detailed introduction to the specific steps:(1)
The ITO glass resistance used in the ITO glass substrate processing experiment is 15 Ω. First, a glass knife is used to scratch a 15 × 60 mm2 glass substrate, and a layer of vacuum tape is stuck on the side where the ITO is deposited to ensure the tape. The edges are neat and there are no air bubbles, especially the edge part; otherwise, it will be corroded. A utility knife is used to scratch the 3 mm × 80 mm tape, the protruding part of the tape is stuck on the back to prevent the ITO at the edge from being corroded, then the ITO glass substrate is attached face-up, a layer of zinc powder in a Petri dish is spread and corroded with concentrated hydrochloric acid for 25∼30 s, the residue attached to the surface is quickly rinsed with a large amount of water, and finally the tape is removed; the substrate with neat edges is selected, and glass is used. The knife is divided into three equal sections and marked on the back for later use.(2)
Preparation of Organic Functional Layer at Present: there are two main methods for making OLED/OPV organic functional layer: small molecule materials generally use vacuum thermal evaporation; polymer materials use wet spin coating technology.(1)
Vacuum Thermal Evaporation: 20 small molecule thermal evaporation process is usually suitable to ensure that the vacuum degree is ∼10–4 Pa. The remaining gas after the vacuum may have a greater impact on the performance of the device.(2)
Wet Spin Coating Process: the wet spin coating process is mainly divided into the following categories: (a) suction sheet spin coating polymers are usually cross-linked, easily decomposed by heat, and are not easy to evaporate and deposit in the vacuum evaporation chamber. Therefore, in general, it is dissolved in a suitable solvent and deposited on the substrate through a suction sheet spin coating process. However, this limits the properties of the polymer to be soluble; the same solvent can no longer dissolve other polymers; otherwise, the solvent corrosion effect will appear. The production of flexible devices can be based on the principle of similar compatibility between solvents, using different solvents to dissolve different polymers and orderly spin coating to form a film. Although the thickness of the film produced by the spin coating process can be adjusted by controlling the concentration of the polymer in the solution, the spin coating rate, the spin coating temperature, etc., however, it is difficult to produce a film with a certain thickness and control the film thickness by monitoring the deposition process. In the semiconductor display industry, the spin coating process has been applied. However, the production of large-area flat-panel displays cannot be completed smoothly with the spin coating process. (b) Doctor blade process: in this process, the polymer is dissolved in a solvent and then coated on the substrate to form a certain thickness of film thickness, and the excess part is removed by precise doctor blade technology. Compared with the spin coating process, it is easier to make a relatively thick film, but the thickness of the film must not be less than 100 nm. This process is more common in the production of OLEDs. (c) Wet injection molding method: Yang et al. used inkjet printing technology to make OLEDs, which is a major advancement in the wet film manufacturing process. Compared with the wet sucking sheet spin coating process, wet injection molding technology can be used to make double-layer PLEDs, that is, adding organic layers that are not compatible with each other.


## 3.2. Characterization of Physical and Chemical Properties of Materials Made of Light-Emitting Devices Based on Mononuclear Platinum and Iridium Complexes

The thermal stability of mononuclear platinum and iridium metal-organic complexes P1 and P2 are calibrated, as shown in Figure7. Under the protection of nitrogen, the thermal weight loss of the two mononuclear complexes was measured at a temperature program rate of 20°C/min. The two complexes P1 and P2 have good thermal stability, and the temperature (Td) at 5% mass loss is 307°C and 292°C, respectively.Figure 7
Molecular structures of P1 and P2 complexes.The UV-visible absorption spectra of the two mononuclear metal complexes P1 and P2 in CH2Cl2 (10–5 M) are shown in Figure8, and the relevant parameters are shown in Table 3.1. P1 exhibits three absorption peaks with different intensities near 240, 335, and 353 nm. P2 exhibits two weak absorption peaks with different intensities in the 260 nm and 350–450 nm regions. Among them, 240 nm and 260 nm are the π − π∗ transition absorption of platinum-iridium mononuclear metal, the absorption peak at 350∼450 nm is the transition absorption from the metal to the ligand, and the absorption of P1 at 330 nm and 350 nm the peak is attributed to the transition absorption of MLCT.Figure 8
UV-visible light absorption spectrum of metal complexes P1 and P2.Figure9 shows that in CH2Cl2, the complexes P1 and P2 have strong emission peaks near 475 nm and 497 nm. The emission peak around 475 nm can be attributed to the 1MLCT transition emission, and the emission around 497 nm can be attributed to the 3MLCT transition emission. At the same time, we studied the electrochemical properties of the two materials. The HOMO and LUMO energy levels of the material are obtained by the following empirical formula:(11)HLUMO=−Hred+4.38Ev,HLUMO=−H0x+4.38Ev,Hg=−HLUMO+HHOMOEv.Figure 9
PL spectrum of metal complexes P1 and P2 in CH2CI2.The LUMO and HOMO energy levels of P1 areELUMO=3.46Ev and ELUMO=6.63Ev, respectively; the LUMO and HOMO energy levels of P2 are ELUMO=3.2Ev and ELUMO=5.62Ev, respectively.


## 3.3. Characterization of Electroluminescence Performance of Light-Emitting Devices Based on Mononuclear Platinum and Iridium Complexes

The electroluminescence spectrum of the mononuclear platinum complex P1 device at a voltage of 8 V is shown in Figure10. The electroluminescence emission peak of PVK + PBD undoped metal complex device is shown in Figure 10.Figure 10
EL spectrum of metal complexes.It can be seen from Figure10that when the doping ratio is 1%, the EL spectrum presents three peaks: 450nm, 500nm, and 650nm. The peak at 431 nm is attributed to the emission peak of PVK. Starting from the doping concentration of 2%, as the doping ratio increases, the luminescence intensity of PVK at 431 nm gradually decreases, indicating that the concentration increases and the energy transfer efficiency between PVK and P2 gradually increases, which inhibits the luminescence of PVK. At the same time, the increase in the doping concentration also increases the proportion of the metal complexes directly capturing the carrier emission, and the increase in the concentration also causes the complexes to produce exciplex emission, which changes the spectrum.When P1: (PVK + PBD) doping concentration is 0.5%, the spectra under different driving voltages are shown in Figure11. With the increase in the voltage, there is basically no change in the position of the emission peak at 431 nm, but when the voltage is increased to 12 V, the emission intensity of PVK decreases and the excimer emission between the complexes increases. It shows that this luminescence should be related to the environment in which the excited state P1 molecule is located. This is consistent with the phenomenon described in articles reported in the literature. As the voltage increases, the number of carriers increases, the number of potential wells formed by the guest material increases, the number of carriers directly trapped increases, and the luminescence intensity increases, making the luminescence of PVK relatively weak.Figure 11
1EL spectrum under different voltages.The EL spectrum under different voltages is shown in Figure11. The comparison of experimental results shows that when the doping ratio is 1%, the EL spectrum shows three peaks: 431 nm, 476 nm, and 530 nm. The emission peak of P2 has many similarities with P1. The emission peak of PVK is at 431 nm, the emission peak of P2 itself is at 476 nm, and the emission peak at 530 nm is derived from the emission of the excimer between P2 molecules (excimer emission). Starting from the doping concentration of 2%, as the doping ratio increases, the luminescence intensity of PVK at 431 nm gradually decreases, indicating that the concentration increases and the energy transfer efficiency between PVK and P2 gradually increases, which inhibits the luminescence of PVK. At the same time, it can be seen that the emission intensity at 476 nm of P2 gradually decreases, and the emission intensity at 530 nm gradually increases. The decrease in emission intensity at 476 nm may be due to the absorption effect of the complex itself. The increase in luminescence intensity at 530 nm may be due to the increase in doping ratio, and there is interaction between molecules, the probability of transition between molecules increases, and the formation of excimer luminescence.Although the ignition voltage of platinum and iridium mononuclear complexes is relatively low, which is basically between 7 V and 9 V, the white light region luminescence spectrum is obtained, but pure white light is not obtained.


## 4. Optimization and Performance Research Analysis of Organic Photovoltaic Devices

### 4.1. The Influence of Different Solvents on the Performance of Polymer Devices

The experimental donor material is the copolymer PFO-3-ThPz-Tpa, and the molecular formula is shown in Figure12. The acceptor material is PC61BM, and chlorobenzene (CB) and dichlorobenzene (DCB) are used as solvents.Figure 12
Copolymer PFO-3-ThPz-Tpa structure formula.Due to the difference in the solubility of polymers in different solvents, the morphology of the prepared photosensitive film is different, and the morphology of the photosensitive layer will have a great influence on the photovoltaic characteristics of the device. The polymer PFO-3-ThPz-Tpa has good solubility in aromatic solvents chlorobenzene and dichlorobenzene, and PCBM has good solubility in these two solvents. Therefore, we choose two solvents, chlorobenzene and dichlorobenzene, to make two different photosensitive layers, and the AFM morphology is shown in Figure13.Figure 13
PFO-3-ThPz-Tpa blend AFM morphology of different solvents.The photovoltaic performance of the device is tested under 100 mW/cm2 intensity of light. The photovoltaic performance parameters when DCB is used as a solvent are η = 1.87%, Jsc = 7.83 mA/cm2, Voc = 0.67 V, and FF = 36%; when CB is used as solvent, the photovoltaic performance parameters are η = 2.09%, Jsc = 7.51 mA/cm2, Voc = 0.76 V, and FF = 37%. These differences in photovoltaic performance are due to the different solubility of donor and acceptor materials in different solvents and different solvent volatility, which will have a greater impact on the morphology and phase separation of the film. A suitable solvent can make the two phases fully miscible, to increase the contact area of the donor and acceptor heterojunction phases and form a good interpenetrating network structure, which is conducive to the separation of excitons and the transport of electrons and holes. The recombination of photo-generated carriers is reduced.


### 4.2. The Performance of Polymer Devices with Different Ratios of Donors and Acceptors

In the experiment, we used P3HT as the donor material and PC61BM as the acceptor to study the effect of blends in different proportions on the morphology of the photosensitive layer. The results are shown in Table1.Table 1
Blended photovoltaic parameters of P3HT/PC61BM under different ratios.
P3HT/PC61BMJ (mA/cm2)V%FF1 : 112.210.654.080.511210.850.683.850.521 : 38.090.782.750.441 : 47.140.852.390.38With the increase in the proportion of PCBM, P3HT is gradually covered by PCBM. With the further increase in PCBM mass fraction, PCBM micro-islands in the bulk heterojunction gradually form large islands, which affects the formation of interpenetrating network structure, and the overall performance of photovoltaic cells decreases. In the photovoltaic cell of the P3HT: PC61BM blend system, if the mass ratio of PC61BM is less than 47%, the photovoltaic cell cannot form an effective electron transmission path. When the mass ratio of PCBM is higher than 60%, PC61BM aggregates to form a large island structure that hinders the transmission of electrons and reduces the efficiency of photovoltaic cells. The experiment found that the best ratio of P3HT:PC61BM blending system is 1 : 1. The best ratio of MDMO-PPV:PCBM system and MEH-PPV:PC61BM system is 1 : 4.


### 4.3. The Influence of Additive DIO on the Performance of Polymer Devices

In the experiment, 1,8-diiodooctane (DIO) was used as the interface modifier, and the blend PFO-3-ThPz-Tpa: PC61BM (wt%, 1 : 3) used chlorobenzene as the solvent. A small amount of DIO is added to the polymer blend solution, the volume percentage of DIO and chlorobenzene (CB) is 0%, 2%, 4%, and 8%, the concentration of the solution is 24 mg/mL, and the thickness of the active layer is about 95 nm, the annealing temperature is 150°C, and the annealing time is 15 min. The phase separation and nanomorphology of the obtained bulk heterojunction polymer fullerene film are improved.Table2 lists the performance parameters of the device doped with different proportions of DIO. From the table, it can be seen that the additive DIO has a significant effect on the fill factor and efficiency of the device. When the proportion of additives is 2%, the fill factor reaches the maximum FF = 0.43, and the efficiency is increased by 12% compared with the absence of additives. As the proportion of additives increases, the efficiency begins to decrease, and the fill factor also begins to decrease. This is due to the addition of DIO, and the donor and acceptor form an interpenetrating network structure, forming an effective two-phase separation structure; with the increase in the amount of DIO, the interface contact area between the donor and acceptor is reduced, resulting in stimulation. The separation efficiency of electrons and the transmission efficiency of holes (electrons) are reduced. It can be seen from Figure 14 that the interface morphology changes after the addition of DIO. In addition, the addition of a relatively high proportion of additives is equivalent to increasing the amount of traps in the active layer, which in turn reduces the performance of the device.Table 2
Photovoltaic parameters of doped different ratios of DIO.
DIO:CBJ (mA cm2)VFF%07.520.760.372.092%7.480.740.442.354%7.240.750.381.988%6.230.750.361.69Figure 14
CB AFM image for solvent.


### 4.4. The Influence of Different Cathode Interface Modification Layers on the Performance of Polymer Devices

The physical properties such as humidity and interlayer adhesion of organic and inorganic materials have an important impact on the life and performance of the device. However, in the development of organic photovoltaic devices, the influence of the morphology and charge extraction/recombination of the electrode/organic interface film is often ignored. PCBM is used as the acceptor material, and the polymer PFO-FCz-DBT30 is used as the donor. The structural formula is shown in Figure15. The ultraviolet absorption spectrum is shown in Figure 16.Figure 15
PFO-FCz-DBT30 molecular structure diagram.Figure 16
Ultraviolet absorption spectrum of PFO-FCz-DBT30.PFO-FCz-DBT30 has two strong absorption peaks at 393 nm and 532 nm. The experimentally measured LUMO and HOMO energy levels of the polymer PFO-FCz-DBT30 are ELUMO = −3.34 eV, EHOMO = −5.22 eV, Egel = 1.68 eV, and Egopt = 1.87 eV, respectively.The dark current-voltage and photocurrent-voltage characteristics of the device are all tested by Keithley 2602. The light source is AM1.5G 100 mW/cm2, and the test process is carried out under ambient room temperature conditions of 48 atmospheres. The photovoltaic characteristic parameters of the device are shown in Table 3.Table 3
Different modified interfaces and performance parameters of photovoltaic devices.
Interface modificationJVFF%NO4.560.660.230.65LiF4.360.80.260.9Ca3.740.770.260.78CsF4.230.870.270.99It can be seen from the table that with the introduction of LiF and CsF interface modification layers, the Voc of the device has been improved, but the Jsc has decreased. In electroluminescent devices, there are related literature reports that inserting a LiF interface modification layer between the polymer layer and the Al electrode layer can increase the stability of the device and reduce the electron injection barrier in OLEDs.In the experiment, we found that in PFO-FCz-DBT30 the open-circuit voltage of the PCBM blend system photovoltaic device is not ELUMO(A)-EHOMO(D) = െ3.91 eV(5.22 eV), nor is it a two-electrode work function. The difference between ITO/PEDOT work function is 5.1∼5.2 eV, but is somewhere in between.


## 4.1. The Influence of Different Solvents on the Performance of Polymer Devices

The experimental donor material is the copolymer PFO-3-ThPz-Tpa, and the molecular formula is shown in Figure12. The acceptor material is PC61BM, and chlorobenzene (CB) and dichlorobenzene (DCB) are used as solvents.Figure 12
Copolymer PFO-3-ThPz-Tpa structure formula.Due to the difference in the solubility of polymers in different solvents, the morphology of the prepared photosensitive film is different, and the morphology of the photosensitive layer will have a great influence on the photovoltaic characteristics of the device. The polymer PFO-3-ThPz-Tpa has good solubility in aromatic solvents chlorobenzene and dichlorobenzene, and PCBM has good solubility in these two solvents. Therefore, we choose two solvents, chlorobenzene and dichlorobenzene, to make two different photosensitive layers, and the AFM morphology is shown in Figure13.Figure 13
PFO-3-ThPz-Tpa blend AFM morphology of different solvents.The photovoltaic performance of the device is tested under 100 mW/cm2 intensity of light. The photovoltaic performance parameters when DCB is used as a solvent are η = 1.87%, Jsc = 7.83 mA/cm2, Voc = 0.67 V, and FF = 36%; when CB is used as solvent, the photovoltaic performance parameters are η = 2.09%, Jsc = 7.51 mA/cm2, Voc = 0.76 V, and FF = 37%. These differences in photovoltaic performance are due to the different solubility of donor and acceptor materials in different solvents and different solvent volatility, which will have a greater impact on the morphology and phase separation of the film. A suitable solvent can make the two phases fully miscible, to increase the contact area of the donor and acceptor heterojunction phases and form a good interpenetrating network structure, which is conducive to the separation of excitons and the transport of electrons and holes. The recombination of photo-generated carriers is reduced.


## 4.2. The Performance of Polymer Devices with Different Ratios of Donors and Acceptors

In the experiment, we used P3HT as the donor material and PC61BM as the acceptor to study the effect of blends in different proportions on the morphology of the photosensitive layer. The results are shown in Table1.Table 1
Blended photovoltaic parameters of P3HT/PC61BM under different ratios.
P3HT/PC61BMJ (mA/cm2)V%FF1 : 112.210.654.080.511210.850.683.850.521 : 38.090.782.750.441 : 47.140.852.390.38With the increase in the proportion of PCBM, P3HT is gradually covered by PCBM. With the further increase in PCBM mass fraction, PCBM micro-islands in the bulk heterojunction gradually form large islands, which affects the formation of interpenetrating network structure, and the overall performance of photovoltaic cells decreases. In the photovoltaic cell of the P3HT: PC61BM blend system, if the mass ratio of PC61BM is less than 47%, the photovoltaic cell cannot form an effective electron transmission path. When the mass ratio of PCBM is higher than 60%, PC61BM aggregates to form a large island structure that hinders the transmission of electrons and reduces the efficiency of photovoltaic cells. The experiment found that the best ratio of P3HT:PC61BM blending system is 1 : 1. The best ratio of MDMO-PPV:PCBM system and MEH-PPV:PC61BM system is 1 : 4.


## 4.3. The Influence of Additive DIO on the Performance of Polymer Devices

In the experiment, 1,8-diiodooctane (DIO) was used as the interface modifier, and the blend PFO-3-ThPz-Tpa: PC61BM (wt%, 1 : 3) used chlorobenzene as the solvent. A small amount of DIO is added to the polymer blend solution, the volume percentage of DIO and chlorobenzene (CB) is 0%, 2%, 4%, and 8%, the concentration of the solution is 24 mg/mL, and the thickness of the active layer is about 95 nm, the annealing temperature is 150°C, and the annealing time is 15 min. The phase separation and nanomorphology of the obtained bulk heterojunction polymer fullerene film are improved.Table2 lists the performance parameters of the device doped with different proportions of DIO. From the table, it can be seen that the additive DIO has a significant effect on the fill factor and efficiency of the device. When the proportion of additives is 2%, the fill factor reaches the maximum FF = 0.43, and the efficiency is increased by 12% compared with the absence of additives. As the proportion of additives increases, the efficiency begins to decrease, and the fill factor also begins to decrease. This is due to the addition of DIO, and the donor and acceptor form an interpenetrating network structure, forming an effective two-phase separation structure; with the increase in the amount of DIO, the interface contact area between the donor and acceptor is reduced, resulting in stimulation. The separation efficiency of electrons and the transmission efficiency of holes (electrons) are reduced. It can be seen from Figure 14 that the interface morphology changes after the addition of DIO. In addition, the addition of a relatively high proportion of additives is equivalent to increasing the amount of traps in the active layer, which in turn reduces the performance of the device.Table 2
Photovoltaic parameters of doped different ratios of DIO.
DIO:CBJ (mA cm2)VFF%07.520.760.372.092%7.480.740.442.354%7.240.750.381.988%6.230.750.361.69Figure 14
CB AFM image for solvent.


## 4.4. The Influence of Different Cathode Interface Modification Layers on the Performance of Polymer Devices

The physical properties such as humidity and interlayer adhesion of organic and inorganic materials have an important impact on the life and performance of the device. However, in the development of organic photovoltaic devices, the influence of the morphology and charge extraction/recombination of the electrode/organic interface film is often ignored. PCBM is used as the acceptor material, and the polymer PFO-FCz-DBT30 is used as the donor. The structural formula is shown in Figure15. The ultraviolet absorption spectrum is shown in Figure 16.Figure 15
PFO-FCz-DBT30 molecular structure diagram.Figure 16
Ultraviolet absorption spectrum of PFO-FCz-DBT30.PFO-FCz-DBT30 has two strong absorption peaks at 393 nm and 532 nm. The experimentally measured LUMO and HOMO energy levels of the polymer PFO-FCz-DBT30 are ELUMO = −3.34 eV, EHOMO = −5.22 eV, Egel = 1.68 eV, and Egopt = 1.87 eV, respectively.The dark current-voltage and photocurrent-voltage characteristics of the device are all tested by Keithley 2602. The light source is AM1.5G 100 mW/cm2, and the test process is carried out under ambient room temperature conditions of 48 atmospheres. The photovoltaic characteristic parameters of the device are shown in Table 3.Table 3
Different modified interfaces and performance parameters of photovoltaic devices.
Interface modificationJVFF%NO4.560.660.230.65LiF4.360.80.260.9Ca3.740.770.260.78CsF4.230.870.270.99It can be seen from the table that with the introduction of LiF and CsF interface modification layers, the Voc of the device has been improved, but the Jsc has decreased. In electroluminescent devices, there are related literature reports that inserting a LiF interface modification layer between the polymer layer and the Al electrode layer can increase the stability of the device and reduce the electron injection barrier in OLEDs.In the experiment, we found that in PFO-FCz-DBT30 the open-circuit voltage of the PCBM blend system photovoltaic device is not ELUMO(A)-EHOMO(D) = െ3.91 eV(5.22 eV), nor is it a two-electrode work function. The difference between ITO/PEDOT work function is 5.1∼5.2 eV, but is somewhere in between.


## 5. Conclusions

At present, the highest energy conversion efficiency of organic photovoltaic cells has reached 10.0 ± 0.3%. With the development of technology, batteries with higher energy conversion efficiency will be developed. At that time, low-power electronic products will get rid of the charging problem, and people’s lives will be more convenient. Organic photovoltaic cells have the advantages of lightweight, softness, and foldability. Organic photovoltaic cells can be designed into various shapes, which are convenient to carry and have certain practical value. Organic photovoltaic cells are bound to highlight their incomparable competitive advantages in future energy wars with their superior performance and low cost. In organic photovoltaic devices, controlling the morphology of the active layer and improving the contact between the interfaces to form ohmic contacts is of great significance to the improvement of device performance. To improve the performance of organic photovoltaic devices, the selection of materials and the optimization of the devices complement each other and are indispensable.



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*Source: 4249657-2022-07-21.xml*