Power Conversion Efficiency Degradation Research Articles

Excellent Intrinsic Long‐Term Thermal Stability of Co‐Evaporated MAPbI3 Solar Cells at 85 °C

AbstractThermal stability is a critical criterion for assessing the long‐term stability of perovskite solar cells (PSCs). Here, it is shown that un‐encapsulated co‐evaporated MAPbI3 (TE_MAPbI3) PSCs demonstrate remarkable thermal stability even in an n‐i‐p structure that employs Spiro‐OMeTAD as hole transport material (HTM). TE_MAPbI3 PSCs maintain over ≈95% and ≈80% of their initial power conversion efficiency (PCE) after 1000 and 3600 h respectively under continuous thermal aging at 85 °C. TE_MAPbI3 PSCs demonstrate remarkable structural robustness, absence of pinholes, or significant variation in grain sizes, and intact interfaces with the HTM, upon prolonged thermal aging. Here, the main factors driving TE_MAPbI3 stability are assessed. It is demonstrated that the excellent TE_MAPbI3 thermal stability is related to the perovskite growth process leading to a compact and almost strain‐stress‐free film. On the other hand, un‐encapsulated PSCs with the same architecture, but incorporating solution‐processed MAPbI3 or Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 as active layers, show a complete PCE degradation after 500 h under the same thermal aging condition. These results highlight that the control of the perovskite growth process can substantially enhance the PSCs thermal stability, besides the chemical composition. The TE_MAPbI3 impressive long‐term thermal stability features the potential for field‐operating conditions.

Simple Adaptive Rectifier with High Efficiency over a Range of 21 dBm Input Power for RF Energy Harvesting Applications

This paper presents a novel simple adaptive and efficient rectifier for Radio Frequency (RF) energy harvesting applications. Traditional rectifiers have maximum RF-DC Power Conversion Efficiency (PCE) over a narrow range of RF input power due to diode breakdown voltage restrictions. The proposed adaptive design helps to extend the PCE over a wider range of RF input power at 2.45GHz using a simple design. Two alternative paths arecontrolled depending on the RF input power level. Low input power levels activate the first path connected to a single rectifier; low power levels make the diode operate below its breakdown voltage and therefore avoiding PCE degradation. High input power levels activate the second path dividing it into three rectifiers. This keeps input power at each rectifier at a low power level to avoid exceeding the diode break down voltage. Simulated PCE of this work is kept above 50% over a range of 21.4 dBm input power from -0.8dBm to 20.6dBm.

Titanium Nanopillar Arrays Functioning as Electron Transporting Layers for Efficient, Anti-Aging Perovskite Solar Cells.

Electron transporting layers (ETLs), required to be optically transparent in perovskite solar cells (PSCs) having regular structures, possess a determinant effect on electron extraction and collection. Metal oxides (e.g., TiO2 ) have overwhelmingly served as ETLs, but usually have low electron mobility (μe < 10-2 cm2 V-1 s-1 ) not favorable for photovoltaic conversion. Here, metal oxides are replaced with metals (e.g., Ti with μe ≈ 294 cm2 V-1 s-1 ) that are sculptured via glancing angle deposition to be a close-packed nanopillar array (NaPA), which vertically protrudes on a transparent electrode to obtain sufficient optical transmission for light harvesting in perovskite. Ti NaPAs, whose rough surfaces are passivated with 5 nm thick TiO2 (i.e., Ti NaPAs@TiO2 ) to suppress exciton recombination, lead to the champion power conversion efficiency (PCE) of 18.89% that is superior to that of MAPbI3 PSCs without Ti NaPAs@TiO2 or containing TiO2 NaPAs@TiO2 , owing to high surface wettability, high μe , and relatively low work function of Ti. Furthermore, Ti NaPAs@TiO2 effectively prevents the decomposition of MAPbI3 to achieve long-term shelf stability whereby 50-day aging only causes 15% PCE degradation. This work paves the way toward widening the material spectrum, from semiconductors to metals, to generate a diverse range of ETLs for producing efficient optoelectronic devices with long-term shelf stability.

Water‐Assisted Crystal Growth in Quasi‐2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

AbstractOrganic–inorganic hybrid quasi‐2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi‐2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water‐controlled crystal growth of quasi‐2D perovskites are presented to achieve high‐efficiency solar cells. It is demonstrated that the (BA)2MA4Pb5I16‐based PSCs (n = 5) processed with water‐containing precursors display an increased short‐circuit current density (Jsc) of 19.01 mA cm−2 and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI∙H2O), leading to modulations on the crystal orientation and phase distribution of various n‐value components, which facilitate interphase charge transfer and charge sweepout throughout the device. The water‐assisted crystallization is further applied to triple cation‐based (BA)2(MA0.8FA0.15Cs0.05)4Pb5I16 quasi‐2D perovskites, which generate a remarkable PCE of 18.04%. Despite the presence of water in the precursors, the devices exhibit a satisfactory thermal stability with the PCE degradation &lt;15% under continuous thermal aging at 60 °C for over 500 h.

Cs-Doped TiO2 Nanorod Array Enhances Electron Injection and Transport in Carbon-Based CsPbI3 Perovskite Solar Cells

Carbon-based CsPbI3 perovskite solar cells (CsPbI3 C-PSCs) without hole-transporting materials have been attracting much attention because of their high stability. However, the electron transport layer (ETL) of TiO2 mesoporous scaffolds has hindered electron transport. Herein, we solve the above problem by employing a Cs-doped TiO2 (Cs-TiO2) nanorod array as an ETL, which provides a direct and fast electron path. Cs doping well increases the free charge carrier density in the TiO2 nanorod array to enhance the electron transport. Besides, electron injection is accelerated because of the upshift of conduction band levels and the improvement in the pore-filling of the perovskite layer. Consequently, CsPbI3 C-PSCs based on Cs-TiO2 nanorod arrays achieved a significantly higher power conversion efficiency (PCE) of 9.5%, compared to the devices based on TiO2 nanorod arrays (5.8%). Furthermore, the nonencapsulated devices based on Cs-TiO2 nanorod arrays show almost no PCE degradation after 3000 h of storage in ambient air (20–30% relative humidity, 20–30 °C).

Cleaning cycle optimization and cost evaluation of module dust for photovoltaic power plants in China

The photovoltaic (PV) power plants installed in the northwest and northeast areas of China have a serious dust pollution problem. In this paper, a model for optimizing the cleaning cycle of module dust and evaluating the cost for the PV power plants in China was proposed by the use of dust deposition monitoring with image recognition and two cleaning technologies. Outdoor experimental results showed that the degradation of power conversion efficiency changed linearly with increasing the image gray value and the dust deposition density had an asymptotic relationship with dust deposition time. Based on the proposed model and corresponding dry and wet cleaning technologies, the optimal cleaning cycles for a PV power plant in northeast China were approximately 10.1 and 22.8 days when the power conversion efficiency was reduced by 4.5% and 10.2%, respectively. The annual cost resulting from dust on the PV power modules in China was estimated to be $0.0161–0.0222 million per MW with current fixed cleaning cycle and wet cleaning technology. However, the annual cost could be reduced to 36.5–50.3% by using the optimized cleaning cycle and applying dry cleaning technology.

Performance and stability improvement of single junction a-Si:H solar cell by interface engineering

In this study, the influence of p/i interface on the stability of amorphous silicon solar cells has been investigated by light-induced degradation study. To peruse this study a series of p-i-n solar cells with and without p/i interface buffer layer have been fabricated using plasma enhanced chemical vapor deposition (PECVD) technique. In the light soaking experiment, the samples were kept under one sun illumination for 1000 h. The degradation results reveal that the stability of the solar cell with buffer layer at p/i interface has significantly improved. It has been found that the solar cell with p/i buffer layer has only 13.42% degradation in power conversion efficiency after 1000 h light soaking. Whereas the cell without any interface treatment, the degradation in efficiency has reached 23.56%. The quantum efficiency and dark current measurement were also performed to establish the correlation between interface degradation and stability of the a-Si:H solar cells. Our extensive light soaking studies indicate that the light-induced degradation in a-Si:H solar cell is not only a bulk or material degradation effect. The p/i interface deterioration also has a major influence on the instability of the cell. Based on this hypothesis, a solar cell designed through proper device engineering has shown improved performance and stability against light soaking.

Hysteresis-Less CsPbI2Br Mesoscopic Perovskite Solar Cells with a High Open-Circuit Voltage Exceeding 1.3 V and 14.86% of Power Conversion Efficiency

High-performance and hysteresis-less mesoscopic CsPbI2Br perovskite solar cells (PSCs) are demonstrated by adapting hole-transporting materials (HTMs) with controlled highest occupied molecular orbital (HOMO) values. The used model HTMs are poly-3-hexylthiophene (P3HT), poly-triarylamine (P-TAA), poly-fluoren-8-triarylamine (PF8-TAA), and poly-indenofluoren-8-triarylamine (PIF8-TAA), and their HOMO energy levels position to -4.98, -5.09, -5.45, and -5.52 eV, respectively. By controlling the HOMO of the HTMs, the average open-circuit voltages of 25 mesoscopic CsPbI2Br PSCs are controllable from 1.11 ± 0.030 V for a P3HT HTM-based device to 1.17 ± 0.023, 1.21 ± 0.027, and 1.27 ± 0.028 V for P-TAA, PF8-TAA, and PIF8-TAA HTM-based devices. As a result, the PIF8-TAA HTM-based mesoscopic PSC exhibits the highest open-circuit voltage of 1.31 V and power conversion efficiency (PCE) of 14.20% for the forward scan condition and 14.86% for the reverse scan condition under 1 sun illumination (100 mW/cm2 AM 1.5G). In addition, the unencapsulated mesoscopic CsPbI2Br PSCs exhibited 10-14% of PCE degradation compared to their initial efficiency in maximum power point tracking under continuous 1 sun light soaking at 85 °C for 1000 h.

Cu-doped nickel oxide interface layer with nanoscale thickness for efficient and highly stable printable carbon-based perovskite solar cell

The power conversion efficiency (PCE) of hole conductor free carbon-based perovskite solar cells (PSCs) is restricted by the poor charge extraction and recombination losses at the carbon-perovskite interface. For the first time we successfully demonstrated incorporation of thin layer of copper doped nickel oxide (Cu:NiOx) nanoparticles in carbon-based PSCs, which helps in improving the performance of these solar devices. Cu:NiOx nanoparticles have been synthesized by a facile chemical method, and processed into a paste for screen printing. Extensive X-ray Absorption Spectroscopy (XAS) analysis elucidates the co-ordination of Cu in a NiOx matrix and indicates the presence of around 5.4% Cu in the sample. We fabricated a monolithic perovskite module on a 100 cm2 glass substrate (active area of 70 cm2) with a thin Cu:NiOx layer (80 nm), where the champion device shows an appreciated power conversion efficiency of 12.1% under an AM 1.5G illumination. To the best of our knowledge, this is the highest reported efficiency for such a large area perovskite solar device. I-V scans show that the introduction of Cu:NiOx mesoporous scaffold increases the photocurrent, and yields fill factor (FF) values exceeding 57% due to the better interface and increased hole extraction efficiency. Electrochemical Impedance Spectroscopy (EIS) results reinforce the above results by showing the reduction in recombination resistance (Rrec) of the PSCs that incorporates Cu:NiOx interlayer. The perovskite solar modules with a Cu:NiOx layer are stable for more than 4500 h in an ambient environment (25 °C and 65% RH), with PCE degradation of less than 5% of the initial value.

High-Performance and Stable Mesoporous Perovskite Solar Cells via Well-Crystallized FA0.85MA0.15Pb(I0.8Br0.2)3.

The overall performance of perovskite solar cells (PSCs) depends particularly on the chemical composition and crystalline quality of the perovskite light harvester. Here, the well-crystallized mixed-cation lead mixed-halide perovskite films with the optimized composition of FA0.85MA0.15Pb(I0.8Br0.2)3 were achieved by antisolvent-assisted single-step spin-coating in ambient conditions. The resulting PSCs with the well-crystallized FA0.85MA0.15Pb(I0.8Br0.2)3 exhibit impressive power conversion efficiency (PCE) over 20% under standard AM 1.5 illumination with excellent reproducibility. Remarkably, no perceivable degradation in PCE was detected from the PSCs stored in ambient conditions without any encapsulation after 7000 h (nearly 300 days), which was among the best shelf stability ever reported for PSCs. The superior performance was mainly attributed to the improved structural quality of the FA0.85MA0.15Pb(I0.8Br0.2)3 layer with reduced grain boundaries, reduced trap-state density, and prolonged carrier lifetime, as well as the better intrinsic stability of the mixed perovskite with an optimized composition.

Management of Crystallization Kinetics for Efficient and Stable Low-Dimensional Ruddlesden-Popper (LDRP) Lead-Free Perovskite Solar Cells.

Low‐dimensional Ruddlesden–Popper (LDRP) lead‐free perovskite has great potential due to its improved stability and oriented crystal growth, which is mainly attributed to the effective control of crystallization kinetics. However, the crystallization kinetics of LDRP lead‐free perovskite films are highly limited by Lewis theory. Here, the management of the crystallization kinetics of LDRP tin (Sn) perovskite films jointly controlled by Lewis adducts and the ion exchange process using a mixture of polar aprotic solvent dimethyl sulfoxide (DMSO) and ion liquid solvent methylammonium acetate (MAAc) (the process named as “L‐I”) is demonstrated. Homogeneous nucleated LDRP Sn perovskite films with average grain size close to 9 µm are achieved. Both low electron and hole defect density with a magnitude of 1016, high carrier mobility, and excellent electrical performance are obtained. As a result, the LDRP Sn perovskite solar cell (PSC) with power conversion efficiency (PCE) of 4.03% is achieved using a simple one‐step method without antisolvents, which is one of the best LDRP Sn PSCs. Most importantly, the PSC exhibits excellent stability with no degradation in PCE after 94 d in a nitrogen atmosphere owing to the high‐quality film and the inhibition of the oxidation of Sn2+.

High-performance metal-oxide-free perovskite solar cells based on organic electron transport layer and cathode

Abstract We introduced phenyl-C61-butyric acid methyl ester (PCBM) as an electron transport layer to improve the performance of metal-oxide-free perovskite solar cells (PSCs) using high-conductivity poly(3,4-ethylenedioxylenethiophene):poly(styrene sulfonate) (PEDOT:PSS) as the cathode. The work function of the PEDOT:PSS was tuned from −5.08 to −4.05 eV by using polyethylenimine, improving the electron collection. Using PCBM improved the electron transport and suppressed the charge recombination of the PSCs. The power-conversion efficiency (PCE) of the rigid PSCs (on glass substrates) was significantly improved from 12.5% to 13.9%, and the open-circuit voltage, short-circuit current density, and fill factor were improved simultaneously. The long-term stability of the PSCs was also improved: the PCE degradation of the PSCs without encapsulation decreased from 18.4% to 13.0% after 114 h. Using a 37-nm PCBM layer, the flexible PSCs on polyethylene naphthalate substrates exhibited a high PCE of 11.4% with good bendability. Our results indicate that using PCBM as an electron transport layer in metal-oxide-free PSCs is a feasible method for the large-scale roll-to-roll production of PSCs.

Low-temperature-processed ZnO thin films as electron transporting layer to achieve stable perovskite solar cells

Morphology and surface property of ZnO thin films as electron transporting layer in perovskite solar cells are crucial for obtaining high-efficient and stable perovskite solar cells. In this work, two different preparation methods of ZnO thin films were carried out and the photovoltaic performances of the subsequent perovskite solar cells were investigated. ZnO thin film prepared by sol–gel method was homogenous but provided high series resistance in solar cells, leading to low short circuit current density. Lower series resistance of solar cell was obtained from homogeneous ZnO thin film from spin-coating of colloidal ZnO nanoparticles (synthesized by hydrolysis–condensation) in a mixture of 1-butanol, chloroform and methanol. The perovskite solar cells using this film achieved the highest power conversion efficiency (PCE) of 4.79% when poly(3-hexylthiophene) was used as a hole transporting layer. In addition, the stability of perovskite solar cells was also examined by measuring the photovoltaic characteristic for six consecutive weeks with the interval of 2 weeks. It was found that using double layers of the sol–gel ZnO and ZnO nanoparticles provided better stability with no degradation of PCE in 10 weeks. Therefore, this work provides a simple method for preparing homogeneous ZnO thin films in order to achieve stable perovskite solar cells, also for controlling their surface properties which help better understand the characteristics of perovskite solar cells.

Precursor effects on methylamine gas-induced CH3NH3PbI3 films for stable carbon-based perovskite solar cells

Carbon-based perovskite solar cells (PSCs) without hole transport material have attracted much attention due to their high stability. However, their power conversion efficiency (PCE) is still low because of the lack of suitable perovskite deposition methods. In this work, a facile solid-gas reaction method was explored to prepare high quality perovskite and the effects of precursor composition (PbI2, PbI2 + HI, HPbI3 and PbI2 + NH4I) on the CH3NH2 (MA) gas-induced perovskite were systematically investigated. The lack of H+/I− and/or HI suppressed the conversion of PbI2 precursor to MAPbI3, while rapid and complete conversion was achieved for (PbI2 + HI), HPbI3 and (PbI2 + NH4I) precursors. Compared with HPbI3 precursor, the presence of H2O molecules in (PbI2 + HI) precursor lowered the perovskite crystallinity, while the release of NH3 from (PbI2 + NH4I) precursor slower the interaction of MA molecules with MAPbI3 for achieving the highest quality MAPbI3 layer. The application of an anti-solvent treatment during precursor deposition further improved the quality of HPbI3 and (PbI2 + NH4I)-processed perovskite layers, which as a result, significantly promoted the photovoltaic performance of C-PSCs. Both devices exhibited considerably high stability, especially for the (PbI2 + NH4I)-processed C-PSCs, who did not show any PCE degradation after storage in air atmosphere at room temperature for 120 days.

High-performance inverted two-dimensional perovskite solar cells using non-fullerene acceptor as electron transport layer

Ruddlesden–Popper type two-dimensional (2D) and quasi-2D perovskite-based photovoltaics have been attracting increasing attention due to their high power conversion efficiency (PCE) and long-term stability. In this work, we fabricated inverted 2D perovskite solar cells (PSCs) using a non-fullerene acceptor as electron transport material. Employing a 55-nm thick 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthienyl)-dithieno[2,3-d:2′,3′-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene (ITIC-Th) as electron transport layer, an average PCE of 8.4% was achieved for the 2D PSCs, which was comparable to that of 2D PSCs based on phenyl-C61-butyric acid methyl ester (PCBM). However, the long-term stability of the 2D PSCs was improved as the degradation of PCE was reduced from 19.8 to 14.6% following a 15-day duration, which can be attributed to the strong hydrophobic property of the ITIC-Th. The best sample based on the 55-nm thick ITIC-Th exhibited a high PCE of 8.9% with a stable power output and negligible hysteresis, indicating the superior electron transport property of ITIC-Th. Our results demonstrate that ITIC-Th is an effective alternative to PCBM to fabricate highly efficient and stable 2D PSCs.

The Stability of CdS QDSCs Based on Optimized MWCNs/CuS Counter Electrodes

In order to enhance the stability of CdS quantum dot sensitized solar cells (QDSCs), the CdS quantum dots (QDs) sensitizer is loaded with ZnS QDs as a passivation layer and Pt counter electrode (CE) material is replaced by multiwall carbon nanotubes (MWCNTs) combined with CuS QDs. The microstructure of CEs is observed by SEM and TEM. The results show acid-treated MWCNTs can possess a larger specific surface area resulting in loading more CuS QDs. CuS QDs with uniform nanometer size are deposited on the external wall of acid-treated MWCNTs. The electrocatalytic activity of CEs is analyzed by electrochemical impedance spectroscopy (EIS) and Tafel curves. The results exhibit that the electrocatalytic activity of acid-treated MWCNTs improves after the introduction of CuS QDs. Under 24 h one-sun illumination, the electrocatalytic activity of Pt CEs decreases remarkably, even less than acid-treated MWCNTs/CuS QDs CEs. The photoelectric property of QDSCs is analyzed with J–V curves. The photoelectric parameters of QDSCs can be improved considerably after loading CuS QDs into acid-treated MWCNT CEs. Power conversion efficiency (PCE) of the QDSC with acid-treated MWCNTs/CuS QDs CE is lower than that of Pt CE based one, but after 24 h one-sun illumination, it does not change in comparison with sharp PCE degradation of the Pt CE based QDSC. The mechanism of improved QDSC stability is discussed systematically through optimizing the CEs.

Performance and stability of semitransparent OPVs for building integration: A benchmarking analysis

Semitransparent (ST) organic photovoltaics (OPVs) are demonstrating great potential for building integration applications, especially in windows. For that purpose, ST-OPVs should achieve adequate transparency and performance stability. In this regard, the present research deals with the experimental performance of three different building-integrated ST-OPV technologies (technology A: developed in the frame of the present study; technologies B and C: commercial modules). More specifically, spectral transmittance and electrical measurements have been conducted in order to determine the characteristics of the modules for building integration and electricity generation purposes. Results regarding the transmittance reveal that technology A outperforms technologies B and C. The stability analysis of the modules verifies that module C is the most stable one with almost no decrease (3.6%) in the power conversion efficiency (PCE). Furthermore, the PCE of technology B is slightly higher than in the case of technology C, which experiences a PCE degradation of about 10–15% over the whole time period. Finally, technology A presents a 20% reduction in PCE at around 500 h.

Single Component Organic Solar Cells Based on Oligothiophene‐Fullerene Conjugate

AbstractA new donor (D)–acceptor (A) conjugate, benzodithiophene‐rhodanine–[6,6]‐phenyl‐C61 butyric acid methyl ester (BDTRh–PCBM) comprising three covalently linked blocks, one of p‐type oligothiophene containing BDTRh moieties and two of n‐type PCBM, is designed and synthesized. A single component organic solar cell (SCOSC) fabricated from BDTRh–PCBM exhibits the power conversion efficiency (PCE) of 2.44% and maximum external quantum efficiency of 46%, which are the highest among the reported efficiencies so far. The SCOSC device shows efficient charge transfer (CT, ≈300 fs) and smaller CT energy loss, resulting in the higher open‐circuit voltage of 0.97 V, compared to the binary blend (BDTRh:PCBM). Because of the integration of the donor and acceptor in a single molecule, BDTRh‐PCBM has a specific D–A arrangement with less energetic disorder and reorganization energy than blend systems. In addition, the SCOSC device shows excellent device and morphological stabilities, showing no degradation of PCE at 80 °C for 100 h. The SCOSC approach may suggest a great way to suppress the large phase segregation of donor and acceptor domains with better morphological stability compared to the blend device.

Degradation in perovskite solar cells stored under different environmental conditions

Investigations carried out on the degradation of perovskite solar cells (PSCs) stored in different open air environmental conditions are reported here. The solar cells were stored in the open in the dark inside the laboratory (relative humidity 47 ± 5%, temperature 23 ± 4 °C), under compact fluorescent lamp (CFL) illumination (irradiance 10 mW cm2, relative humidity 47 ± 5%, temperature 23 ± 4 °C) and under natural sunlight outside the laboratory. In the outdoor storage situation the surrounding conditions varied from time to time and the environmental conditions during the day (irradiance 100 mW/cm2, relative humidity ~18%, temperature ~45 °C at noon) were entirely different from those at night (irradiance 0 mW/cm2, relative humidity ~66%, temperature ~16 °C at midnight). The photovoltaic parameters were measured from time to time inside the laboratory as per the International Summit on Organic Photovoltaic Stability (ISOS) protocols. All the photovoltaic parameters, such as short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE), of the solar cells stored outdoors decayed more rapidly than those stored under CFL or in the dark. The solar cells stored in the dark exhibited maximum stability. While the encapsulated solar cells stored outdoors were completely dead after about 560 h, the solar cells stored under CFL illumination retained >60% of their initial efficiency even after 1100 h. However, the solar cells stored in the dark and tested up to ~1100 h did not show any degradation in PCE but on the contrary exhibited slight improvement, and this improvement was mainly because of improvement in their Voc. Rapid degradation in the open air outside the laboratory under direct sunlight compared with the dark and CFL storage has been attributed to high temperature during the day, high humidity at night, high solar illumination intensity and the presence of ultra-violet and infra-red radiation in incident solar light. Under CFL storage the top Ag electrode decomposed and reacted with the active layer. The decomposition and reaction of Ag electrode was accelerated in the outdoor conditions under direct sunlight. These results suggest that Ag is a good electrode material for efficient PSCs but is not good for their long term stability.

Efficient Inverted ITO-Free Organic Solar Cells Based on Transparent Silver Electrode with Aqueous Solution-Processed ZnO Interlayer

Efficient inverted organic solar cells (OSCs) with the MoO3(2 nm)/Ag (12 nm) transparent cathode and an aqueous solution ZnO electron extraction layer processed at low temperature are investigated in this work. The blend of low bandgap poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methylester (PC71BM) is employed as the photoactive layer here. A power conversion efficiency (PCE) of 5.55% is achieved for such indium tin oxide- (ITO-) free OSCs under AM 1.5G simulated illumination, comparable to that of ITO-based reference OSCs (PCE of 6.11%). It is found that this ZnO interlayer not only slightly enhances the transparency of MoO3/Ag cathode but also obtains a lower root-mean-square (RMS) roughness on the MoO3/Ag surface. Meanwhile, ITO-free OSCs also show a good stability. The PCE of the devices still remains above 85% of the original values after 30 days, which is slightly superior to ITO-based reference OSCs where the 16% degradation in PCE is observed after 30 days. It may be instructive for further research of OSCs based on metal thin film electrodes.