ITO Cathode Research Articles

Highly efficient inverted organic light-emitting devices by tuning particle size of ZnO nanoparticles

Inverted organic light-emitting devices (OLEDs) have been extensively researched because they can provide many advantages such as low driving voltage and high environmental stability in display applications. However, the electron injection is a critical issue in the inverted OLEDs because the work function of the ITO cathode is too high to inject electrons from the cathode into the adjacent organic layer. In this paper, we enhanced the electron injection by tuning the particle size of ZnO nanoparticles (NPs). Hexagonal wurtzite ZnO NPs with different size were synthesized by the solution precipitation method. As the particle size increases, the photoluminescence spectrum in the visible region shifts to the long wavelength due to the narrowing of band gap. The electrical resistivity decreases with increasing the particle size. The inverted phosphorescent OLEDs with a tris(2-phenylpyridine)iridium(III) emitter have been fabricated using ZnO NPs with different size. As the particle size increases from 3.0 to 6.2 nm, the enhanced injection of electrons from the ZnO NPs to the organic electron transport layer results in the decrease of the driving voltage and the increase of the maximum external quantum efficiency (EQE). The maximum EQE of 26.02 % was achieved in the inverted OLEDs with 6.2 nm ZnO NPs.

Effect of Oxidizing Agent on the Synthesis of ZnO Nanoparticles for Inverted Phosphorescent Organic Light-Emitting Devices without Multiple Interlayers.

Inverted organic light-emitting devices (OLEDs) have been aggressively developed because of their superiorities such as their high stability, low driving voltage, and low drop of brightness in display applications. The injection of electrons is a critical issue in inverted OLEDs because the ITO cathode has an overly high work function in injecting electrons into the emission layer from the cathode. We synthesized hexagonal wurtzite ZnO nanoparticles using different oxidizing agents for an efficient injection of electrons in the inverted OLEDs. Potassium hydroxide (KOH) and tetramethylammonium hydroxide pentahydrate (TMAH) were used as oxidizing agents for synthesizing ZnO nanoparticles. The band gap, surface defects, surface morphology, surface roughness, and electrical resistivity of the nanoparticles were investigated. The inverted devices with phosphorescent molecules were prepared using the synthesized nanoparticles. The inverted devices with ZnO nanoparticles using TMAH exhibited a lower driving voltage, lower leakage current, and higher maximum external quantum efficiency. The devices with TMAH-based ZnO nanoparticles exhibited the maximum external quantum efficiency of 19.1%.

High-performance and selective semi-transparent perovskite solar cells using 3D-structured FTO

Perovskite solar cells (PSCs) have been in the spotlight as a promising next-generation solar cell. With the tremendous development of power conversion efficiency (PCE) over the past decades, a considerable amount of research has focused on semi-transparent perovskite solar cells for applications. However, the short-circuit current density (JSC) greatly decreases in semi-transparent PSCs with an increase in transmittance, and this results in a significant decrease in PCE. In this study, semi-transparent PSCs were fabricated by controlling the absorption layer thickness and aperture ratio using a 3D-structured FTO manufactured via processes that can work large areas (direct printing and mist-CVD). This strategy has an advantage in that the aperture ratio (transmission/entire area) can be controlled easily by adjusting pattern specification. The effect of a 3D-structured FTO enhanced the diffuse transmittance and shortened the carrier travel distance; further, it minimized the decrease in PCE because of an increase in transmittance. Our fully semi-transparent PSCs (F–PSCs) with the ITO cathode achieved a PCE of 12.0 %–14.6 %, and an average visible transmittance (AVT) of 13.4 %–17.0 %. These results demonstrate that the parameter of semi-transparent PSCs (transmittance and PCE) can be easily tailored to the application by controlling the specification of the pattern.

Plasma damage-free deposition of transparent Sn-doped In2O3 top cathode using isolated plasma soft deposition for perovskite solar cells

We developed an isolated plasma soft deposition (IPSD) technique for the plasma damage-free deposition of a Sn-doped In2O3 (ITO) top cathode on semi-transparent perovskite solar cells (PSCs). Unlike the directly faced plasma in conventional magnetron sputtering, the isolated plasma region in the IPSD process prevents the direct irradiation of plasma and facilitates plasma damage-free sputtering. Effective confinement of high-density plasma in isolated regions by using a specific Nd-Fe-B45 magnet array also prevents irradiation of energetic particles sputtered from faced ITO targets. In addition, linear scanning of the substrate in the isolated plasma region resulted in a low-temperature and large-area coating of the ITO top cathode without plasma damage for semi-transparent PSCs. Without intentional substrate heating, the IPSD-processed ITO film with a thickness of 100 nm under optimal conditions exhibited a low sheet resistance of 33.02 Ohm/square, high optical transmittance of 91.27%, root mean square roughness of 0.252 nm, and work function of 4.33 eV. To demonstrate the feasibility of IPSD, we fabricated PSCs with thermally evaporated perovskite active layers. Compared with the power conversion efficiency (PCE: 4.35%) of PSCs with magnetron-sputtered ITO cathode, the PSC with IPSD-processed ITO cathode exhibited a similar PCE (15.52%) because of the absence of plasma damage. Considering the commercialization of PSCs, the IPSD-based top cathode coating process possesses great potential as a key technique for bidirectional or semi-transparent PSCs.

Electric Control of Exchange Bias at Room Temperature by Resistive Switching via Electrochemical Metallization.

Electric field control of exchange bias (EB) plays an important role in spintronics due to its attractive merit of lower energy consumption. Here, we propose a novel method for electrically tunable EB at room temperature in a device with the stack of Si/SiO2/Ta/Pt/Ag/Mn-doped ZnO (MZO)/Pt/FeMn/Co/ITO by resistive switching (RS) via electrochemical metallization (ECM). The device shows enhanced and weakened EB when set at high-resistance state (HRS) and low-resistance state (LRS), respectively. For the device at LRS, the aberration-corrected scanning transmission electron microscopy (STEM) characterizations unambiguously reveal that the Ag filaments grow initially from the Ag anode and then elongate toward the ITO cathode. It is inferred that at LRS, a small portion of Ag filaments have passed through the MZO and the intervening thin Pt layer and extended into the FeMn layer. After applying reverse voltage, these Ag filaments are electrochemically dissolved and ruptured near the MZO/Pt interface. This is considered to be the main mechanism responsible for RS and switchable EB as well. This work presents a new strategy for designing low-power, nonvolatile magnetoelectric random access memory devices.

An investigation of design principles toward near infrared organic upconversion devices

Among the reported Near-infrared (NIR) Organic upconversion devices (OUDs), the devices realized by utilizing NIR sensitive bulk heterojuntion (BHJ) as sensitizers and normal OLED as emitters have been demonstrated as the most typical structure which exhibited higher photon-to-photon conversion efficiency than other OUDs. In this paper, NIR OUDs by integrating lead phthalocyanine (PbPc):C60 BHJ as sensitizer with normal OLED and inverted OLED as emitter were both fabricated and studied. And the impact of carrier blocking layers on the performance of the devices were investigated. Especially for OUDs based on inverted OLED, MoO3 as buffer layer, copper phthalocyanine (CuPc) and 1, 4-bis(1-naphthylphenylamino) biphenyl (NPB) as electron blocking layer (EBL) was inserted between the ITO cathode and the BHJ sensitizer, respectively. It was demonstrated that OUDs with CuPc EBL exhibited best performance, which signified that the performance of the devices can be effectively improved via introducing an electron blocking layer with high hole mobility. Moreover, the brightness and pixel-less imaging capability of both types OUDs dependent on applied voltages in the dark and under illumination were investigated.

Alcohol-Soluble Zwitterionic 4-(Dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate Small Molecule as a Cathode Modifier for Nonfullerene Acceptor-Based Organic Solar Cells.

A new zwitterionic small molecule 4-(dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate (PAS), synthesized from 2-dimethylaminopyrindine (2-DMAP), was developed for the ITO cathode modifier. PAS and 2-DMAP dissolved in methanol can form a thin layer on ITO cathode by a simple spin-coating process. The heteroatom moieties in 2-DMAP (sp2 and sp3 nitrogen) and PAS (sp2 nitrogen and sulfonate ion) can coordinate to the ITO surface and decrease the ITO work function by the induced surface dipoles. The fullerene-based (PBDTT-FTTE:PC71BM) inverted OSCs using PAS and 2-DMAP interlayer can achieve PCEs of 8.95 and 8.26%, respectively, which are superior to the devices without a modifier (PCE = 3.25%) and comparable to the corresponding ZnO-based device (PCE = 8.57%). Nevertheless, 2-DMAP, like other nitrogen-containing polymer interlayer materials, turns out to be not applicable to inverted organic solar cells (I-OSCs) with IT-4F as the n-type electron acceptor because the amino group of 2-DMAP can act as a nucleophile to attack the end-group of IT-4F at the interface. The decomposition of IT-4F by 2-DMAP was carefully proved to be via retro-aldol condensation. As a result, the device (PBDBT-F:IT-4F) modified with 2-DMAP displayed a low PCE of 7.34%. The zwitterionic PAS with reduced nucleophilicity and basicity can modify the ITO surface without decomposing IT-4F. The PBDBT-F:IT-4F-based device modified with PAS maintained a high PCE of 11.41%. Most importantly, the PAS-based device using the well-known Y6 acceptor (PBDBT-F:Y6) can achieve a PCE of 13.82%. This new interfacial material can be universally applied to I-OSCs employing various A-D-A-type acceptors installed with the electrophilic 1,1-dicyanamethylene-5,6-difluoro-3-indanone (FIC) end-group.

Progress of electron injection of ITO cathode for inverted organic light-emitting diodes

Progress of electron injection of ITO cathode for inverted organic light-emitting diodes

Semi-transparent perovskite solar cells with bidirectional transparent electrodes

Abstract In this study, we report on high performance semi-transparent perovskite solar cells (PSCs) with bidirectional transparent electrodes for use in building-integrated photovoltaics (BIPV). Using a typical magnetron sputtered InSnO (ITO) anode and a low energy sputtered InZnSnO (IZTO) cathode, we fabricated bidirectional transparent electrodes for semi-transparent PSCs. In particular, by the sequential sputtering of a thin buffer and then a thick dense IZTO layer (two-step sputtering), we fabricated a transparent IZTO cathode for a p-i-n planar type PSC without any plasma damage. Compared to the power conversion efficiency (PCE 3.43%) of PSCs with an ITO cathode prepared by typical DC magnetron sputtering, the PSC with a two-step sputtered IZTO cathode showed a much higher PCE (15.72%) due to the absence of plasma damage. The high PCE of the semi-transparent PSC with IZTO cathode is comparable to the PCE (17.04%) of an opaque PSC with opaque Ag cathode. Furthermore, with diluted perovskite solution, we able to achieve PCE of 13.61% and AVT of 24.70% both high enough to use as PSC for BIPV. These results demonstrate that the two-step linear facing target sputtering (FTS) process is a feasible approach to make high-quality transparent top cathodes for semi-transparent PSCs. Considering the mass-production of semi-transparent PSCs for BIPV, FTS-based two-step sputtering has great potential to become a key technique for producing smart windows that will replace typical solution coating or other complicated transfer processes.

Highly efficient inverted polymer solar cells based on ethanolamine-treated indium tin oxide as cathode

Abstract Significant performance enhancement has been realized for inverted polymer solar cells (PSCs) with the device structure of glass/indium tin oxide (ITO)/P3HT:PC61BM/MoO3/Ag (P3HT, poly(3-hexyl- thiophene-2,5-diyl), and PC61BM, phenyl-C61-butyric acid methyl ester) by ethanolamine (ETA)-treated ITO as cathode by spin-coating. The power conversion efficiency (PCE) of the inverted PSC increases from 2.64% to 4.95% after ETA treatment, which is also higher than that of a normal device with ZnO as electron-transport layer. The surface characteristics of ETA-treated ITO were studied by contact angle, AFM, UPS, XPS, and PL measurements. As a result, ETA treatment can significantly reduce surface roughness, surface defects, surface potential, and photo-exciton quenching of ITO due to the ETA molecules absorbed on the surface of ITO cathode. This facile ETA-treated surface engineering provides a promising method to enhance the performance of inverted PSCs with ITO as cathode.

Functionalization of fullerene by polyethylene glycol toward promoted electron transport in inverted polymer solar cells

Abstract A novel polyethylene glycol-functionalized fullerene derivative (C60-PEGA) was synthesized by a facile one-step nucleophilic addition reaction. C60-PEGA possessed good solubility in methanol and was estimated as C60-(C8H18N)13H13O with average PEG moiety of 13 by 1H NMR, FT-IR and X-ray photoelectron spectroscopy (XPS). C60-PEGA was applied as an ETL to construct inverted bulk heterojunction polymer solar cells (inverted BHJ-PSCs) based on photoactive layers of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3, 4-b]thiophene-2-carboxylate]: [6,6]-phenyl-C71-butyric acid methyl ester (PTB7-Th: PC71BM), which achieve the best PCE of 9.25%, surpassing that of reference device based on the ZnO ETL (8.61%). The higher ETL performance of C60-PEGA ETL in BHJ-iPSC device relative to that of the ZnO ETL was attributed to the increase of electron mobility and effective electron transport from the active layer to the ITO cathode because that the reduced work function (WF) of ITO via the modification of C60-PEGA leads to the increase of short-circuit current density (Jsc) and consequent PCE.

Passivation effect of composite organic interlayer on polymer solar cells

Abstract Highly efficient inverted polymer solar cells were demonstrated by incorporating a polyfluorene electrolyte to mitigate the intrinsic external defects of ITO cathode. The interfacial compatibility of solution-processed active layer and the cathode was improved using PFN/PFBT composite interlayer due to the optimized surface morphology and increased interfacial area. The hybrid PFN/PFBT electron transport layer suppressed recombination of the photo-excited carriers at the interface and facilitated subsequent charge transfer into the cathode. The leakage current as well as the series resistance of the device was decreased and the device reliability was improved. As a result, the electron collection efficiency from the active layer to the cathode was enhanced and the highest power conversion efficiency of 9.74% was achieved. The incorporated PFBT layer aimed to overcome the intrinsic defects of conventional transparent buffer layer based on the transition metal oxides, which make it spendable to fabricate the commercially viable photovoltaic devices.

Performance enhancement of perovskite solar cells through interfacial engineering: Water-soluble fullerenol C60(OH)16 as interfacial modification layer

Abstract TiO2 is widely used in conventional n-i-p type perovskite solar cells (Pero-SCs) as electron transporting layer (ETL). However, its drawbacks such as photocatalytic properties, low electron mobility, and a process of high temperature sintering, hindered the further improvement of device performance. In this work, a vacuum-deposited fullerene C60 was utilized as ETL, and a easily accessible fullerene derivative, C60(OH)16 fullerenol, was employed between ITO electrode and C60 ETL to modify ITO for the first time. After introducing the C60(OH)16 fullerenol layer, the Pero-SC obtained the favorable energy level alignment between ITO cathode and perovskite layer, and the device based on C60(OH)16/C60 ETL achieved a champion PCE of 16.70%, which showed a 15.41% enhancement compared to the Pero-SC with pristine C60 ETL (14.47%). The mechanisms of performance improvement were systemically discussed with respect to the optimized energy level, efficient charge transport and reduced interfacial resistance. This work exhibited that fullerenol C60(OH)16 is a promising interfacial modification material for the n-i-p type Pero-SCs.

Efficient Inverted Polymer Solar Cells with ITO Cathode Modified by Zinc Oxide and Polyethylene Oxide Bilayers

For inverted polymer solar cells (PSCs), zinc oxide (ZnO) with various advantages are typically used as cathode buffer layer, but the existing surface traps/detects of ZnO layer obviously restrict device performance. In this work, the authors introduce polyethylene oxide (PEO) with high molecular weight of 300 thousands to modify the surface of ZnO layer on ITO cathode for inverted PSCs, where PEO possesses the particular advantages of easy accessibility and low cost. Compared with the ITO modified by pure ZnO and PEO layer, the ITO modified by ZnO/PEO bilayers shows the similarly good transparency, the lowest work function, the best surface morphology, and contact property. ZnO/PEO bilayers can provide the optimal energy alignment and interface contact between ITO and active layer, and efficiently eliminate the surface defects of ZnO layer. Therefore, the ITO/ZnO/PEO-based device exhibits the best photovoltaic performance with the PCE of 9.57% compared to the ITO/ZnO-based device (8.42%) and the ITO/PEO-based device (8.16%). The impressive results suggest that ZnO/PEO bilayers should be promising cathode buffer layer for high-performance inverted PSCs.

Highly efficient inverted organic light-emitting diodes with organic p-n junction as electron injection layer

Organic p-n junction (PNJ) composing of PEDOT:PSS(MoO3)/Bphen:Cs2CO3 is introduced as electron injection layer (EIL) in the bottom-emission inverted organic light-emitting diodes (BIOLEDs). The devices with PNJ of PEDOT:PSS/Bphen:Cs2CO3 or MoO3/Bphen:Cs2CO3 as EIL achieve maximum current efficiency of 87.3 cd/A and 86.6 cd/A and power efficiency of 69.4 lm/W and 63 lm/W, respectively, which are higher than that79.8 cd/A and 60 lm/W of the device with the n-doping Bphen:Cs2CO3 as EIL, and 51% and 55% improvement in the half operational lifetime. The injection of electrons from the interface of PNJ but not directly from the ITO cathode is more effectively comparison with conventional BIOLED with n-doped Bphen:Cs2CO3 as EIL. Thus, reducing the charge accumulation between the electrode and the organic electron transport layer (ETL), moreover, the PNJ is able to control the injection equilibrium of the carriers, and improve the efficiency and stability of the device.

Enhanced Electroluminescence from ZnO Quantum Dot Light‐Emitting Diodes via Introducing Al2O3 Retarding Layer and Ag@ZnO Hybrid Nanodots

AbstractShort‐wavelength light‐emitting diodes (LEDs), a prevalent research topic in modern optoelectronics, have attracted considerable attention in recent years because of their vast application potential in both civil and military domains. Herein, blue‐violet LEDs are constructed via a spin‐coating solution‐processed ZnO quantum dots (QDs) onto p‐GaN: Mg wafers. By inserting a thin Al2O3 dielectric retarding layer into the ZnO QDs side, electrons injected from ITO cathode are effectively slowed and detained in the QDs emissive layer, resulting in a ≈30‐fold improvement of near‐UV electroluminescence intensity from this p‐GaN/ZnO QDs/Al2O3/ZnO QDs LED. Furthermore, by replacing pure ZnO QDs with Ag@ZnO hybrid nanodots (synthesized through a simple one‐step wet chemical route) as the electron transport layer, the device electroluminescence intensity is further increased. Time‐resolved and temperature‐dependent spectroscopy reveals that both the spontaneous emission rate and internal quantum efficiency of the ZnO QDs active layer are simultaneously increased as a result of the exciton‐localized surface plasmon resonant coupling, which leads to the observed blue‐violet electroluminescence enhancement.

Cathode modification with solution-processed hybrid electron extraction layer for improved charge collection of planar heterojunction perovskite solar cells

Abstract Optimal interface modification of perovskite solar cells is critical to achieve efficient and balanced charge transport and collection. We herein demonstrated that a solution-processed hybrid cathode interfacial layer composed of polyetyleneimine ethoxylate and a lithium quinolate complex improves photovoltaic performance of the planar heterojunction perovskite solar cells. The hybrid cathode modifier effectively lowered work function of ITO cathode, which afforded efficient electron transport and collection at ITO. Furthermore, surface roughness of ITO was significantly decreased, leading to enlarged grain size in densely-packed perovskite thin film. Consequently, the perovskite solar cells with hybrid electron extraction layer generated maximum power conversion efficiency up 15.21%, which is 25% improved value than that without hybrid electron extraction layer. Furthermore, highly-flexible flexible devices with a hybrid electron extraction layer exhibited a promising efficiency of 14.41%, demonstrating its potential for high performance perovskite solar cells.

Chemical Modification of n-Type-Material Naphthalene Diimide on ITO for Efficient and Stable Inverted Polymer Solar Cells.

To provide orthogonal solvent processable surface modification and improve the device stability of bulk-heterojunction polymer solar cells (PSCs), n-type semiconducting material naphthalene diimide (NDI) was chemically introduced onto the ITO surface as a cathode interlayer (CIL) using 3-bromopropyltrimethoxysilane (BrTMS) as a coupling agent. After modification, the work function of ITO can be decreased from 4.70 to 4.23 eV. The modified ITO cathode was applied in inverted PSCs based on PTB7-Th:PC71BM. With the CIL modification, a champion power conversion efficiency (PCE) of 5.87% was achieved, showing a dramatic improvement compared to that of devices (PCE = 3.58%) without CIL. More importantly, with these chemical bonded interlayers, the stability of inverted PSCs was greatly enhanced. The improved PCE and stability can be attributed to the increased open-circuit voltage and the formation of robust chemical bonds in NDI-TMS films, respectively. This study demonstrated that chemical modification of ITO with n-type semiconducting materials provides an avenue for not only solving the solvent orthogonal problem but also improving the device performance in terms of the PCE and the stability.

Imidazole-Functionalized Fullerene as a Vertically Phase-Separated Cathode Interfacial Layer of Inverted Ternary Polymer Solar Cells.

By using a facile one-pot nucleophilic addition reaction, we synthesized a novel imidazole (IMZ)-functionalized fullerene (C60-IMZ), and applied it as a third component of inverted ternary polymer solar cells (PSCs), leading to dramatic efficiency enhancement. According to FT-IR, XPS spectroscopic characterizations, and elemental analysis, the chemical structure of C60-IMZ was determined with the average IMZ addition number estimated to be six. The lowest unoccupied molecular orbital (LUMO) level of C60-IMZ measured by cyclic voltammetry was -3.63 eV, which is up-shifted relative to that of 6,6-phenyl C61-butyric acid methyl ester (PC61BM). Upon doping C60-IMZ as a third component into an active layer blend of poly(3-hexylthiophene) (P3HT) and PC61BM, the power conversion efficiency (PCE) of the inverted ternary PSCs was 3.4% under the optimized doping ratio of 10 wt %, dramatically higher than that of the control device ITO/P3HT:PC61BM/MoO3/Ag based on the binary P3HT:PC61BM blend (1.3%). The incorporation of C60-IMZ results in enhancement of the absorption of P3HT:PC61BM blend film, increase of the electron mobility of the device, and rougher film surface of the P3HT:PC61BM active layer beneficial for interfacial contact with the Ag anode. Furthermore, C60-IMZ doped in P3HT:PC61BM blend may migrate to the surface of ITO cathode via vertical phase separation as revealed by XPS depth analysis, consequently forming a cathode interfacial layer (CIL), which can lower the work function (WF) of ITO cathode. Thus, the interfacial contact between the active layer and ITO cathode is improved, facilitating electron transport from the active layer to ITO cathode. The effectiveness of C60-IMZ as a vertically phase-separated CIL on efficiency enhancement of inverted ternary PSCs is further verified by doping it into another active layer system comprised of a low-bandgap conjugated polymer, poly(thieno[3,4-b]-thiophene/benzodithiophene) (PTB7), blended with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Under the optimized C60-IMZ doping ratio of 10 wt %, the PCE of the PTB7:PC71BM-based inverted ternary PSC device reaches 5.3%, which is about 2 times higher than that of the control binary device (2.6%).

Paired photoelectrocatalytic reactions of glucose driven by a photoelectrochemical fuel cell with assistance of methylene blue

This paper reports the paired photoelectrocatalytic reactions of glucose (GLU) by capturing the photogenerated electrons and holes from ultraviolet (UV)-excited TiO2 nanoparticles (NPs) with the assistance of methylene blue (MB) in neutral media. The blue MB in a mixed system containing TiO2 NPs and GLU can rapidly capture the photogenerated electrons upon UV irradiation to form colorless leuco methylene blue (LMB), which is recovered in the dark, representing reversible colorimetric reactions controlled by turning on and off UV light. More interestingly, while employing TiO2/ITO photoanode and ITO cathode to assemble a UV-excited photoelectrochemical fuel cell, GLU existing in anode and cathode compartments can act as reducing and oxidizing agents to involve the paired photoelectrocatalytic reactions promoted by the MB/LMB-based reversible redox system. The cell current shows a linear response to GLU between 0.5 and 2.0molL−1. Meanwhile, while adding 2.0molL−1 GLU and 2.0molL−1 GLU/10.0mmolL−1 MB to the anode and cathode compartments, respectively, the assembled photoelectrochemical fuel cell shows open-circuit photovoltage of 0.828V, short-circuit photocurrent density of 29.2μAcm−2, maximum power density of 7.2μWcm−2 at 0.345V under UV irradiation of 55μWcm−2.