Cathode Buffer Layer Research Articles

Influence of molar mass ratio, annealing temperature and cathode buffer layer on power conversion efficiency of P3HT:PC71BM based organic bulk heterojunction solar cell

Abstract In bulk heterojunction (BHJ) solar cells, the molar mass ratio of donor-acceptor polymers, the annealing temperature (T an ) and the cathode buffer layer plays very consequential role in improving the power conversion efficiency (PCE) by tuning the film morphology and enhancing the charge carrier dynamics. A comprehensive understanding of each of these factors is essential in order to optimize the performance of organic solar cells (OSCs). Albeit there are several fundamental reports regarding these factors, an altogether meticulous correlation of these physical processes with experimental evidence of the photo active layer are required. In this work, we systematically analyzed the influence of different molar mass ratio, the annealing temperature (T an ) and the cathode buffer layer of rrP3HT:PC 71 BM based BHJ solar cells and their corresponding photovoltaic performances were correlated carefully with their thin film growth structure and energy level diagram. The device having 1:0.8 molar mass ratio of rrP3HT:PC 71 BM and T an = 150 °C annealing temperature with Bathocuproine (BCP) as the cathode buffer layer having ITO/PEDOT:PSS/rrP3HT:PC 71 BM (molar mass ratio = 1:0.8; (T an = 150 °C)/BCP/Al) configuration showed the best device performance with PCE, ɳ = 4.79%, Jsc = 14.21 mA/cm 2 , V oc = 0.58 V and FF = 57.8%. This drastic variation in PCE of the device having BCP/Al as the cathode contact compared to the other device configurations is due to the coalesced effects of better hole-blocking capacity of BCP along with Al and better phase separation of the active blend layer at 150 °C annealing temperature. These results explicate the cumulate role of all these physical parameters and their combined contribution to the PCE amendment and overall device performance with rrP3HT:PC 71 BM based organic BHJ solar cell.

Efficient Inverted Organic Solar Cells Based on a Fullerene Derivative-Modified Transparent Cathode.

Indium tin oxide (ITO) is a transparent conductive material which is extensively used in organic solar cells (OSCs) as electrodes. In inverted OSCs, ITO is usually employed as a cathode, which should be modified by cathode buffer layers (CBLs) to achieve better contact with the active layers. In this paper, an amine group functionalized fullerene derivative (DMAPA-C60) is used as a CBL to modify the transparent cathode ITO in inverted OSCs based on PTB7 as a donor and PC71BM as an acceptor. Compared with traditional ZnO CBL, DMAPA-C60 exhibited comparable transmittance. OSCs based on DMAPA-C60 show much better device performance compared with their ZnO counterparts (power conversion efficiencies (PCEs) improved from 6.24 to 7.43%). This is mainly because a better contact between the DMAPA-C60 modified ITO and the active layer is formed, which leads to better electron transport and collection. Nanoscale morphologies also demonstrate that the surface of DMAPA-C60-modified ITO is plainer than the ZnO counterparts, which also leads to the better device performance.

Ultra-thin MoOx as cathode buffer layer for the improvement of all-inorganic CsPbIBr2 perovskite solar cells

Controlling the crystallization dynamics is one key in optimizing the performance of perovskite solar cells (PSCs). The present study provides a simple approach using a low temperature stable-transition-film (STF) to prepare highly-dense and pinhole-free CsPbIBr2 thin film with high crystalline quality, as well as a new structural design (FTO/NiOx/CsPbIBr2/MoOx/Au) of all-inorganic perovskite solar cells toward long-term thermal stability. For the first time, we demonstrate that MoOx can independently serve as an outstanding cathode buffer layer on an inorganic perovskite layer. The lower work-function MoOx with ultra-thin thickness (4nm) leads to decreases of the Schottky barrier, the contact resistance and the interface trap-state density. This increases the power conversion efficiency (PCE) of all-inorganic planar PSCs from 1.3% to 5.52%. Inspiringly, the FTO/NiOx/CsPbIBr2/MoOx/Au all-inorganic PSCs were demonstrated to possess excellent long-term thermal stability at high temperatures up to 160°C.

Improved photocurrent of PDPP3T based organic Schottky junctions via solution-processed HAT-CN and TPBi as anode and cathode buffer layers (Phys. Status Solidi A 9∕2017)

Improved photocurrent of PDPP3T based organic Schottky junctions via solution-processed HAT-CN and TPBi as anode and cathode buffer layers (Phys. Status Solidi A 9∕2017)

Investigation of the effect of 2,6-pyridinedimethanol as the cathode buffer layer on the photovoltaic properties

ABSTRACT2,6-pyridinedimethanol (Py-diOH) is applied to the cathode interlayer in inverted polymer solar cells (PSCs) based on the blend of PTB7:PC71BM. A layer of Py-diOH generates a favorable interface dipole at the cathode interface. The power conversion efficiency of the devices with the interlayer reaches up to 7.44% with a Jsc of 14.65 mA/cm2, a Voc of 0.71 V, and a FF of 67.9%, respectively The PCE of the device with Py-2OH is very similar to that of the device with ZnO as the electron collection layer. It is possible to obtain high efficiency PSCs without any high temperature heat treatment.

Cathode modification by the electrostatically self-assembled poly(4-vinylpyridine) derivative for enhancing the performance of polymer solar cells

ABSTRACTA non-conjugated polyelectrolyte, poly(4-vinyl N-ethyl pyridinium bromide) (PVPy-EtBr), is applied to polymer solar cells (PSCs) as a cathode buffer layer either inverted or conventional type polymer solar cells to improve the performances. The Kelvin probe microscopy measurement support the formation of favorable interface dipole at the cathode interface, indicating the reduction of a Schottky barrier for an electron collection from the active layer to the cathode treated with electrostatically self-assembly of PVPy-EtBr. Inverted type PSC with PVPy-EtBr as a cathode buffer layer demonstrate the power conversion efficiency (PCE) of 3.49%, which is better than the device without interlayer (PCE = 2.95%). Most increase in the PCE of the devices with interlayer is resulted from enhancement of the Jsc. This is due to that the reduction of a Schottky barrier at the cathode interface. Conventional type PSC with PVPy-EtBr (3.45%) at the cathode interface also exhibit better the PCE compared to that of the device without interlayer (2.88%).

Enhanced performance in inverted organic light-emitting diodes using Li ion doped ZnO cathode buffer layer

ABSTRACTInverted organic light-emitting diodes (IOLEDs) have great potential application in flat-panel display. In this study, a lithium (Li) ion doped solution processed zinc oxide (Li-ZnO) layer was employed as the cathode buffer layer (CBL) for IOLEDs. The Li-ZnO CBL was prepared by inducing the Li ion of 8-hydroxyquinolatolithium (Liq) to diffuse into ZnO film through thermal annealing the bi-layer ZnO/Liq film. Based on the Li-ZnO CBL with ultraviolet(UV) treatment, the IOLED using tris(8-hydroxyquinoline) aluminum as the emitting layer possessed an optimal current efficiency of 4.42 cd A−1, which was improved by 55% than those of the devices with neat ZnO as CBL. The enhancement of the device performance could be attributed to the enhanced electron mobility and electron injection ability of the Li-ZnO CBL. Our finding indicates that the low-temperature deposited Li-ZnO film has great potential for the application of OLED display.

Efficiency enhancement in DIBSQ:PC71BM organic photovoltaic cells by using Liq-doped Bphen as a cathode buffer layer

We have improved the photovoltaic performance of 2,4-bis[4-(N,Ndiisobutylamino)- 2,6-dihydroxyphenyl] squaraine:[6,6]-phenyl C71-butyric acid methyl ester (DIBSQ:PC71BM) organic photovoltaic (OPV) cells via incorporating Liq-doped Bphen (Bphen-Liq) as a cathode buffer layer (CBL). Based on the Bphen-Liq CBL, a DIBSQ:PC71BM OPV cell possessed an optimal power conversion efficiency of 4.90%, which was 13% and 60% higher than those of the devices with neat Bphen as CBL and without CBL, respectively. The enhancement of the device performance could be attributed to the enhanced electron mobility and improved electrode/active layer contact and thus the improved photocurrent extraction by incorporating the Bphen-Liq CBL. Light-intensity dependent device performance analysis indicates that the incorporating of the Bphen-Liq CBL can remarkably improve the charge transport of the DIBSQ:PC71BM OPV cell and thus decrease the recombination losses of the device, resulting in enhanced device performance. Our finding indicates that the doped Bphen-Liq CBL has great potential for high-performance solution-processed small-molecule OPVs.

Improved photocurrent of PDPP3T based organic Schottky junctions via solution-processed HAT-CN and TPBi as anode and cathode buffer layers

All-solution processed organic Schottky junctions (OSJs) with a near-infrared absorbing donor material poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) of 5 wt.% mixed into [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were fabricated. Solution-processed 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (s-HAT-CN) and N-arylbenzimidazoles (s-TPBi) served as the hole and electron transporting layer (HTL and ETL), which was usually prepared by thermal-evaporation. The power conversion efficiency (PCE) was improved from 1.15 to 1.45%, compared with the control device with traditional poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and bathocuproine (BCP) as the HTL and ETL. It could be ascribed to the efficient hole extraction by s-HAT-CN and smoother surface, and thus, lower trap density of s-TPBi. s-HAT-CN showed a comparable transparency and higher hole mobility than PEDOT:PSS, and was proved to be an efficient and promising HTL for solution-processed OSJs. The dependence of OSJ performances on the evaporation- and solution-processed 4,7-diphenyl-1,10-phenanthroline (Bphen) and TPBi was comparably investigated. s-Bphen and s-TPBi devices both demonstrated a higher photocurrent relative to the evaporation-processed Bphen and TPBi devices.

Research progress of cathode buffer layers of the polymer solar cells

Polymer solar cells (PSCs) have attracted great attention in the clean energy utilization due to their advantages of light weight, low cost and easy fabrication. Recently, the power conversion efficiency (PCE) of the PSCs has been improved gradually. The PCE of the single junction PSCs have been increased over 11%, and the interface buffer layers have become the key factors to significantly influence the device performance. In this review, we summaried the recent progress on the cathode buffer layers (CBLs) of the PSCs. The commonly used CBLs have been introduced from two types: inorganic and organic materials. The inorganic materials include metal oxides, metals and metal compounds. The organic materials include polymers, fullerene derivatives and n-type organic semiconductors. We have also investigated the influences on the device photovoltaic performances by introducing their electric properties, optical properties, energy levels, surface morphology and interface contacts. Finally, we have given a perspective on PSCs.

Spontaneous growth by sol-gel process of low temperature ZnO as cathode buffer layer in flexible inverted organic solar cells

In this study, the sol–gel method was employed to prepare zinc oxide (ZnO) thin films as cathode buffer layers for inverted organic solar cells (IOSCs). We used a low temperature sol-gel process for the synthesis of ZnO thin films, in which the molar ratio of zinc acetate dihydrate (ZAD) to ethanolamine (MEA) was varied; subsequently, using the thin films, we successfully fabricated inverted solar cells on flexible plastic substrates. A ZnO sol–gel was first prepared by dissolving ZAD and MEA in ethylene glycol monomethyl ether (EGME). The molar ratios of ZAD to MEA were set as 1:1.2, 1:1, and 1:0.8, and we investigated the characteristics of the resulting ZnO thin films. We investigated the optical transmittance, surface roughness, and surface morphology of the films. Then, we discussed the reasons about the improvement of the device efficiency. The devices were fabricated using the ZnO thin films as cathode buffer layers. The results indicated that the morphology of the thin films prepared using the ZAD to MEA ratios of 1:1 and 1:0.8 changed to a rippled nanostructure after two-step annealing. The PCE was enhanced because of the higher light absorption in the active layer caused by the nanostructure. The structure of the inverted device was ITO/ZnO/P3HT:PC61BM/MoO3/Ag. The short-circuit current densities (8.59 mA/cm2 and 8.34 mA/cm2) of the devices with films prepared using the ZAD to MEA ratios of 1:1 and 1:0.8 ratios, respectively, and annealed at 125 °C were higher than that of the device containing the ZnO thin film that was annealed at 150 °C. Inverted solar cells with ZnO films that were prepared using the ZAD to MEA ratios of 1:1 and 1:0.8 and annealed at 125 °C exhibited PCEs of 3.38% and 3.30%, respectively. More than that, PCEs of the flexible device can reach up to 1.53%.

Low Temperature Aqueous Solution-Processed ZnO and Polyethylenimine Ethoxylated Cathode Buffer Bilayer for High Performance Flexible Inverted Organic Solar Cells

High performance flexible inverted organic solar cells (OSCs) employing the low temperature cathode buffer bilayer combining the aqueous solution-processed ZnO and polyethylenimine ethoxylated (PEIE) are investigated based on Poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butryric acid methyl ester (P3HT:PC61BM) and Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexy)carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C71-butyric acid methyl ester (PTB-7:PC71BM) material systems. It is found that, compared with pure ZnO or PEIE cathode buffer layer (CBL), the proper combination of low-temperature processed ZnO and PEIE as the CBL enhanced the short circuit current density (JSC), resulting in better device performance. The increased JSC results from the enhanced electron collection ability from the active layer to the cathode. By using the ZnO/PEIE CBL, a power conversion efficiency (PCE) as high as 4.04% for the P3HT:PC61BM flexible device and a PCE as high as 8.12% for the PTB-7:PC71BM flexible device are achieved, which are higher than the control devices with the pure ZnO CBL or pure PEIE CBL. The flexible inverted OSC also shows a superior mechanical property and it can keep 92.9% of its initial performance after 1000 bending cycles with a radius of 0.8 cm. These results suggest that the combination of the low temperature aqueous solution processed ZnO and PEIE can be a promising cathode buffer bilayer for flexible inverted OSCs.

A New Function of N719: N719 Based Solution‐Processible Binary Cathode Buffer Layer Enables High‐Efficiency Single‐Junction Polymer Solar Cells

An N719 based high‐efficiency binary cathode buffer layer (CBL) was developed. The work‐function of the Al cathode was precisely modulated between −3.3 and −3.9 eV due to the cation re‐arrangement between the binary components, induced by finely controlling the binary‐components weight ratio. A 10.50%‐ and 11.46%‐efficiency organic solar cells were reported with the use of the N719 and the binary CBL, respectively.

Direct charge carrier injection into Ga2O3 thin films using an In2O3 cathode buffer layer: their optical, electrical and surface state properties

Conductive Ga2O3 thin films with an In2O3 buffer layer have been prepared on c-plane sapphire substrates using a laser molecular beam epitaxy technique. The effects of the In2O3 buffer layer on the structure and optical, electrical and surface state properties of the Ga2O3 films have been studied. The change in conductivity of the thin films is attributed to different thicknesses of the In2O3 buffer layer, which determine the concentration of charge carriers injected into the upper Ga2O3 layer from the interface of the bilayer thin films. In addition, the increase in flat band voltage shift and capacitance values as the In2O3 buffer layer thickens are attributed to the increase in surface state density, which also contributes to the rapid shrinkage of the optical band gap of the Ga2O3. With transparency to visible light, high n-type conduction and the ability to tune the optical band gap and surface state density, we propose that Ga2O3/In2O3 bilayer thin film is an ideal n-type semiconductor for fabrication of transparent power devices, solar cell electrodes and gas sensors.

Enhanced performance of inverted perovskite solar cells using solution-processed carboxylic potassium salt as cathode buffer layer

Using a novel solution-processed carboxylic potassium salt (F-R-COOK) as cathode buffer layer (CBL), a power conversion efficiency (PCE) of 14.37% is obtained, which is more than 51% increase compared with that of the Ag-only device under similar fabrication conditions. The test result of single electron devices and Electrochemical impedance spectroscopy (EIS) measurements demonstrate that the interlayer decreases charge transport resistance. Ultraviolet photoelectron spectroscopy (UPS) measurements are used to study the interfacial effects induced by the new CBL. It is found that F-R-COOK can reduce the work function of the Ag electrode by forming desired interfacial dipoles. Our work indicates the promising applications of F-R-COOK based CBL in perovskite solar cells and may provide some insights into the design and synthesis of new interfacial materials to further improve the device performance.

Low-Temperature Solution-Processed SnO2 Nanoparticles as a Cathode Buffer Layer for Inverted Organic Solar Cells.

SnO2 recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO2 nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO2 NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO2 NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC60BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO2 NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution-processed SnO2 NPs are considered to be suitable for the low-cost, high throughput roll-to-roll process on a flexible substrate for optoelectronic devices.

Low-temperature dynamic vacuum annealing of ZnO thin film for improved inverted polymer solar cells

Low temperature dynamic vacuum annealing was developed for preparing ZnO cathode buffer layer to improve the performance of IPSCs.

Mechanism of inverted polymer solar cells based on poly(dopamine)/ZnO as composite cathode buffer layer

Inverted polymer solar cells with P3HT:PCBM as active layer are fabricated based on poly(dopamine)/ZnO (PDA/ZnO) as composite cathode buffer layer. Effects of PDA/ZnO composite cathode buffer layer with the different self-polymerization times on the device performance are investigated. According to the results, the short circuit current and photoelectric conversion efficiency of polymer solar cells first increase then decrease with the increase of the self-polymerization time of PDA. For 10-min PDA self-polymerization, the photovoltaic performance of the device achieves the optimal values:open circuit voltage 0.66 V, short circuit curent density 9.70 mA/cm2, fill factor 68.06%, and power conversion efficiency 4.35% under irratiation of light with a strength of 100 mW/cm2. We conclude that the improvement of device performance is due to the PDA/ZnO composite cathode buffer layer reduced the contact resistance between the ZnO and ITO, at the same time, the presence of a large number of nitrogen groups in PDA is advantageous for the electronic collection of the inverted polymer solar cells. Meanwhile, polymer solar cell with PDA/ZnO as composite cathode buffer layer also exhibits excelent stability. In addition, PDA has a strong adhesive force that makes the ZnO interface layer on its surface not easy to fall off. This provides a new way of fabricating the flexible polymer solar cell devices.

TiO2阴极缓冲层对 Rubrene/C70有机太阳能电池性能的改善

TiO₂阴极缓冲层对 Rubrene/C70有机太阳能电池性能的改善

Combined influence of plasmonic metal nanoparticles and dual cathode buffer layers for highly efficient rrP3HT:PCBM-based bulk heterojunction solar cells

The combined influence of plasmonic metal nanoparticles and dual cathode buffer layers resulted in high-performance rrP3HT:PCBM based BHJ solar cells (PCE ∼5.65%).