Stability Of Polymer Solar Cells Research Articles

Hybrid ZnO Electron Transport Layer by Down Conversion Complexes for Dual Improvements of Photovoltaic and Stable Performances in Polymer Solar Cells

Polymer solar cells (PSCs) have shown excellent photovoltaic performance, however, extending the spectral response range to the ultraviolet (UV) region and enhancing the UV light stability remain two challenges to overcome in the development of PSCs. Lanthanide down-conversion materials can absorb the UV light and re-emit it at the visible region that matches well with the absorption of the active layer material PTB7-Th (poly[[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbony]thieno[3,4-b]thiophenediyl]]) and PBDB-T-2F, thus helping to enhance the photovoltaic performance and UV light stability of PSCs. In this research, a down-conversion material Eu(TTA)3phen (ETP) is introduced into the cathode transport layer (ZnO) in PSCs to manipulate its nanostructure morphology for its application in hyperfine structure of PSCs. The device based on the ZnO/ETP electron transport layer can obtain power conversion efficiencies (PCEs) of 9.22% (PTB7-Th–PC71BM ([6,6]-phenylC71-butyric acid methyl ester) device) and 13.12% (PBDB-T-2F–IT-4F device), respectively. Besides, in the research on PTB7-Th-PC71BM device, the stability of the device based on ZnO/ETP layer is prolonged by 70% compared with the ZnO device. The results suggest that the ZnO/ETP layer plays the role of enhanced photovoltaic performance and prolonged device stability, as well as reducing photo-loss and UV degradation for PSCs.

RGO induced structural and microstructural properties of P3HT in the performance and stability of polymer solar cells

With recent technological advancement, interest towards energy efficient flexible devices have grown appreciably. Graphene is one of the most renowned material due to its exclusive physical properties together with ultrahigh specific surface area and high carrier mobility of ∼104 V.s. Filler modified physical properties of reduced graphene oxide (rGO)/Poly[3-hexylthiophene-2,5-diyl] (P3HT) blends with [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) have been reviewed carefully in active layer of the organic solar cells. Physio-chemical properties of rGO modified P3HT blends have been analyzed using peculiar characterization tools such as x-ray diffraction (XRD), scanning electron microscope (SEM), UV–visible (UV–vis), Fourier transform infrared, Raman and photo luminescence (PL) spectroscopic techniques along with cyclic-voltammetry measurements. Open-circuit voltage (Voc) of 0.66 V, current-density (Isc) of ∼10.6 mA cm−2 and efficiency of ∼3.71% have been ascertained for the device with 1.6 wt% of rGO in the active layer. RGO induced additional exciton dissociation sites and efficient carrier transport through the conducting rGO network in the active layer is attributed for the improved performance of the solar cells. The effect of introducing ZnO electron transport layer (ETL) on the device performance as well as the stability of the solar cell is investigated.

Solution‐Processable 2D α‐In2Se3 as an Efficient Hole Transport Layer for High‐Performance and Stable Polymer Solar Cells

Herein, a 2D α‐In2Se3 nanosheet, a binary III–VI group compound semiconductor, is fabricated by liquid‐phase exfoliation method, and the photoelectric properties of α‐In2Se3 material are investigated in depth. It is found that α‐In2Se3 film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, α‐In2Se3 film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D α‐In2Se3 nanosheet is used as a hole transport layer (HTL) in conventional PSCs for the first time, and a relatively high power conversion efficiency (PCE) of 9.58% is achieved with the structure of ITO/α‐In2Se3/PBDB‐T:ITIC/Ca/Al, which is comparable with poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices (9.50%). Interestingly, it is demonstrated that the α‐In2Se3 film possesses excellent thermal stability in the range from room temperature to 280 °C, and a PCE of 9.35% is achieved without annealing treatment of α‐In2Se3 film, which exhibits a great potential of α‐In2Se3 for an annealing‐free approach. Furthermore, the incorporation of α‐In2Se3 HTL also remarkably enhances the long‐term stability of PSCs compared with PEDOT:PSS‐based devices. So, the results show that 2D α‐In2Se3 is a promising candidate to be an efficient and stable hole‐extraction layer.

Mechanistic Insights into the Effect of Polymer Regioregularity on the Thermal Stability of Polymer Solar Cells.

Thermal stability is a bottleneck toward commercialization of polymer solar cells (PSCs). The effect of PCBM aggregation on a multilength scale on the bulk-heterojunction (BHJ) structure, performance, and thermal stability of PSCs is studied here by grazing-incidence small- and wide-angle X-ray scattering. The evolution of hierarchical BHJ structures of a blend film tuned by regioregularity of polymers from the as-cast state to the thermally unstable state is systematically investigated. The thermal stability of PSCs with high polymer regioregularity values can be improved because of the good mutual interaction between polymer crystallites and fullerene aggregates. The insights obtained from this study provide an approach to manipulate the film structure on a multilength scale and to enhance the thermal stability of P3HT-based PSCs.

Novel benzodithiophene type low band gap polymer solar cell application and device stability study with atomic layer deposition encapsulation technique

Novel benzodithiophene type copolymer was synthesized through a solvent evaporation technique. Poly(5-(5-(4, 8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4, 5-b’]dithiophen-2-yl)thiophen-2-yl)-2, 3-bis(3, 4-bis(decyloxy)phenyl)-8-(thiophen-2-yl) quinoxaline) (P-TQTBDT) solar cells were encapsulated with conventional and Atomic Layer Deposition (ALD) techniques. Characterizations of the samples were carried out via nuclear magnetic resonance (NMR), gel permeation chromotagraphy (GPC) and cyclic voltammetry (CV) techniques. Stability studies were carried out both P3HT and P-TQTBDT solar cells for comparison of commercial P3HT and our novel polymer solar cell. Our results confirm that ALD is a promising technique for encapsulation of polymer solar cell since stability of P-TQTBDT improved to 72% durability from 38% durability with ALD encapsulation technique during 300 h under AM1.5 G solar irradiation. P-TQTBDT solar cell showed higher stability (about 10%) than P3HT solar cell for both encapsulation methods. We focused on the stability of polymer solar cell can be improved with ALD encapsulation technique. Our aim was to compare P-TQTBDT polymer solar cell with P3HT solar cell. The stability results of P-TQTBDT showed that P-TQTBDT copolymer could be promising polymer to obtain very high stability of polymer solar cells.

Cold Crystallization Temperature Correlated Phase Separation, Performance, and Stability of Polymer Solar Cells

Summary Fabrication of non-fullerene (NF)-based polymer solar cells (PSCs) has been an arduous task involving various approaches to optimize the morphology of blend film for superior performance. In this work, unique exothermic peaks can be observed in differential scanning calorimetry first heating scan of the blend films, which are assigned to the cold crystallization temperature (TCC) of NF acceptors when blended with different degree of crystallinity polymers, and TCC contains the phase information at quenched stage of the film development. A linear correlation between the phase separation parameters and TCC was established, which helps to select the appropriate donor for a specific acceptor. Utilizing multiple polymer-NF blend systems, we report an expectation TCC value between 210°C and 230°C, which would promise balanced domain size, purity, and consequentially superior performance. Further investigation revealed that TCC can also be used to evaluate the thermal stability.

Small energy loss and high open circuit voltage in conventional structure polymer solar cells with the mixture thin films of polyethylenimine ethoxylated and TiOX as the electron extraction layer and Ag as the cathode

One of the challenges facing the fabrication of high-performance conventional structure polymer solar cells (PSCs) is the development of new interface materials that have better air stability and charge carrier collection and transport ability. In this study, the mixture thin films of polyethylenimine ethoxylated (PEIE) and TiOX are developed as the electron extraction layer (EEL) and Ag as the cathode for the application in PSCs, replacing the Ca/Al composite cathode. Ultraviolet photoelectron spectroscopy (UPS) and space-charge-limited current (SCLC) measurements demonstrate that PEIE:TiOX/Ag shows appropriate energy levels, substantially reduced barrier potential, weakened charge carrier recombination and enhanced electron mobility. As a result, the PEIE:TiOX-based PSCs demonstrate not only an enhanced power conversion efficiency (PCE) of 10.94% but also the photovoltaic performance insensitive to the storage time, yielding an aged PCE that is 92% of the fresh PCE. This result can be further explained by the dependence of the charge carrier mobility on storage time. Our work suggests exploiting the PEIE:TiOX/Ag composite thin films as the composite cathode replacing Ca/Al thin films for successfully enhancing the photovoltaic performance and improving the stability of PSCs.

Pyridine-based additive optimized P3HT:PC61BM nanomorphology for improved performance and stability in polymer solar cells

Photovoltaic (PV) performance of bulk heterojunction polymer solar cells (BHJ PSCs) highly depends on the optoelectronic properties of the photoactive layer. In this regard, additives (solvent or solid) are considered as one of the versatile methods and key morphology directing agents for solution processed PV devices. Herein this contribution, we rationally utilize a new kind of pyridine-based solid additives (2-hydroxypyridine (2-DHP) and 2,4-dihydroxypyridine (2,4-DHP)) to manipulate and engineer the nanomorphology of the poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) photoactive system, that can influence the optoelectronic properties for enhanced performance in BHJ PSCs. The optical, electrical, morphological, surface, structural characteristics of the fabricated BHJ PSCs were systematically examined. The atomic force microscopy and X-ray photoelectron spectra measurements confirmed the structural reorganization, phase separation of polymer and fullerene domains resulting in the formation of well-ordered blend in the additive based devices. BHJ PSCs fabricated with P3HT:PC61BM:2-DHP and P3HT:PC61BM:2,4-DHP yielded a best power conversion efficiency (PCE) of 4.35% and 3.58%, respectively, which in contrast outperformed than the PCE obtained from P3HT:PC61BM device (3.01%). The remarkably improved performance for P3HT:PC61BM:2-DHP can be attributed to the enhanced short-circuit current density induced by the morphology optimization. Additionally, the devices fabricated with the solid additives (2-DHP and 2,4-DHP) exhibited improved air-stability due to the oxygen insensitivity of the functional groups present in the chosen additives. The pyridine and hydroxyl groups in 2-DHP and 2,4-DHP possibly form the intermolecular interactions with the photoactive components (P3HT/PC61BM), contribute to the morphology optimization and subsequent PV performance enhancement in BHJ PSCs. It is believed that our findings can inspire and trigger further advanced research toward the design and development of stable and highly efficient BHJ PSCs by rationally choosing low-cost solid additives.

Improving the efficiency and stability of non-fullerene polymer solar cells by using N2200 as the Additive

Polymer solar cells (PSCs) based on small molecule non-fullerene acceptors typically have a range of disadvantages including unfavorable thermal stability and charge carrier transportation. Here, we developed a high-performance non-fullerene ternary PSCs by incorporating a narrow-bandgap polymer acceptor N2200 into a binary blend film comprising of a wide-bandgap conjugated polymer PTzBI-2FP and a small-molecule non-fullerene acceptor ITIC-4F. The resulting ternary devices exhibit an outstanding power conversion efficiency of 13.0%, which is attributable to the efficient energy transfer, enhanced charge carrier mobility, and improved morphology. These findings indicate that the selection of an appropriate third polymer component that affords improved photovoltaic performance and thermal stability, representing a facile and promising route to enhance the performance and stability of PSCs.

The effect of dihydronaphthyl-based C60 bisadduct as a third-component material on Charge-Carrier dynamics, photovoltaic performance, and stability

We describe a ternary photoactive layer based on PffBT4T-2OD as a donor with a blend of dihydronaphthyl-based C60 bisadduct (NCBA) and PC71BM as the acceptor. It offers ideal exciton dissociation, an ideal charge-carrier recombination and photovoltaic performance relationship, and improves the power-conversion efficiency (PCE) and stability of polymer solar cells (PSCs). NCBA has a broad visible-light absorption spectrum and shallower lowest unoccupied molecular orbital (LUMO) energy levels, which enhance exciton dissociation and charge-carrier transport and suppress charge-carrier recombination. This remarkably increases the photocurrent density and fill factor. An optimized PCE of 9.79% was achieved for the ternary PffBT4T-2OD:NCBA:PC71BM(1:0.24:0.96)-based PSCs. The mechanism was exciton dissociation at the PffBT4T-2OD/NCBA, PffBT4T-2OD:PC71BM, and NCBA/PC71BM interfaces. This simultaneously enhances the exciton-dissociation ratio and charge-carrier transport. Meanwhile, PSCs with 20% NCBA as third-component materials exhibit improved thermal stability and photo-stability leading to a lower ratio of PCE under long-time thermal-annealing and visible-light-illuminated treatment. This work indicates that NCBAs are third-component materials that significantly improve PSC performance.

Effect of Side-Chain Engineering of Bithienylbenzodithiophene-alt-fluorobenzotriazole-Based Copolymers on the Thermal Stability and Photovoltaic Performance of Polymer Solar Cells

Side-chain engineering of conjugated polymer donor materials is an important way for improving photovoltaic performances of polymer solar cells (PSCs). On the basis of the polymer J61 synthesized in our group, here, we design and synthesize three new 2D-conjugated polymers J62, J63, and J64 with different types of side chains to further investigate the effect of side chain on their physicochemical and photovoltaic properties. With the narrow bandgap n-type organic semiconductor (n-OS) ITIC as acceptor, the optimized PSCs based on polymer donor of J62 with linear octyl, J63 with linear unsaturated hexylene, and J64 with cyclohexane side chains display power conversion efficiency (PCE) of 10.81%, 8.13%, and 8.59%, respectively. After thermal treatment at 200 °C for 2 h on the active layer,the PCE of the PSC based on J63 still keeps 92% of the original value, which verifies that the cross-linking of the polymer can improve the thermal stability of PSCs. Morphological studies show that the active layer based ...

High-Performance Ternary Nonfullerene Polymer Solar Cells with Both Improved Photon Harvesting and Device Stability.

Efficiency and stability of polymer solar cells (PSCs) are the two most significant decisive factors for the purpose of actual applications. Here, highly efficient and stable ternary PSCs were fabricated by incorporating two well-compatible polymer donors (poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b;4,5- b0]dithiophene-2,6-diyl- alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b]thiophene-)-2-carboxylate-2-6-diyl] and poly[[9-(1-octylnonyl)-9 H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]) with one narrow band gap nonfullerene acceptor (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3- d:2',3'- d']- s-indaceno[1,2- b:5,6- b']dithiophene)). It is found that Förster resonance energy transfer acts as an efficient pathway to further strengthen photon harvesting in this ternary system, which results in a significant improvement in current density ( JSC) without sacrificing the strong absorption of binary blends in the near-infrared region. Meanwhile, both of the inverted and conventional ternary PSCs exhibit better stability compared with the related binary PSCs in air condition because of the interlocked morphology in ternary films. The optimized ternary PSCs exhibit an outstanding power conversion efficiency (PCE) of 9.53% resulting from the synchronous improvements in JSC and fill factor. Moreover, this ternary strategy can be further confirmed by the use of an ultranarrow-band gap nonfullerene acceptor IEICO-4F, and the champion PCE of ternary PSCs reaches to 12.15%.

Sulfanilic Acid Pending on a Graphene Scaffold: Novel, Efficient Synthesis and Much Enhanced Polymer Solar Cell Efficiency and Stability Using It as a Hole Extraction Layer.

In this contribution, we describe a novel, facile, and scalable methodology for high degree functionalization toward graphene by the reaction between bulk graphite fluoride and in situ generated amine anion. Using this, the rationally designed sulfanilic acid pending on a graphene scaffold (G-SO3H), a two-dimensional (2D) π-conjugated counterpart of poly(styrenesulfonate), is available. Combined reliable characterizations demonstrate that a very large quantity of sulfanilic blocks are linked to graphene through the foreseen substitution of carbon-fluorine units and an unexpected reductive defluorination simultaneously proceeds during the one-step reaction, endowing the resultant G-SO3H with splendid dispersity in various solvents and film-forming property via the former, and with recovered 2D π-conjugation via the latter. Besides, the work function of G-SO3H lies at -4.8 eV, well matched with the P3HT donor. Awarded with these fantastic merits, G-SO3H behaves capable in hole collection and transport, indicated by the enhanced device efficiency and stability of polymer solar cells (PSCs) based on intensively studied P3HT:PCBM blends as an active layer. In particular, comparison with conventional poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) and recently rising and shining graphene oxide, G-SO3H outperforms above 17 and 24%, respectively, in efficiency. More impressively, when these three unencapsulated devices are placed in a N2-filled glovebox at around 25 °C for 7 weeks, or subject to thermal treatment at 150 °C for 6 h also in N2 atmosphere, or even rudely exposed to indoor air, G-SO3H-based PSCs exhibit the best stability. These findings enable G-SO3H to be a strongly competitive alternative of the existing hole extraction materials for PSC real-life applications.

Thermally Stable High-Performance Polymer Solar Cells Enabled by Interfacial Engineering.

Interfacial engineering plays an important role in determining the performance and stability of polymer solar cells (PSCs). In this study, thermally stable highly efficient PSCs are fabricated by incorporating a solution-processed cathode interfacial layer (CIL), including 4,4'-({[methyl(4-sulfonatobutyl)ammonio]bis(propane-3,1-diyl)}bis(dimethylammoniumdiyl))bis(butane-1-sulfonate) (MSAPBS) and polyethylenimine (PEI). For PSCs based on blends of poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-[4-(2-ethylhexyl)-3fluorothieno[3,4-b]thiophene-2-carboxylate-2,6-diyl]} (PBDTTT-EFT) and [6,6]-phenyl C71 -butyric acid methyl ester (PC71 BM), the maximum power conversion efficiency (PCE) of inverted PSCs reaches 8.1 % and 7.2 % for MSAPBS and PEI CILs, respectively. The inverted PEI devices exhibit remarkable stability (lifetime >6000 h) under accelerated thermal aging (at 80 °C in ambient environment), which is much superior to that of the device with commonly used LiF CIL (lifetime≈33 h). This stability represents the best result reported for PSCs. The promising results based on this strategy can stimulate further work on the development of novel CILs for PSCs and pave the way towards the realization of commercially viable PSCs with high performance and long-term stability.

Ternary polymer solar cells based on two highly efficient fullerene acceptors with high efficiency and stability under long-time thermal annealing treatment

By introducing a dihydronaphthyl-based C60 bisadduct (NCBA) small molecule acceptor as an third component materials to typical polymer donor:fullerene acceptor binary polymer solar cells (PSCs), we demonstrate that the short-circuit current density (JSC), open circuit voltage (VOC), fill factor (FF), power conversion efficiency (PCE), and thermal stability can be enhanced simultaneously. The ternary photoactive layer enhances photogenerated charge-carrier generation efficiency through complementary short wavelength visible-light absorption between the donor molecule and fullerene acceptors. Simultaneously, the improved PSC performance is mainly attributed to the enhanced exciton dissociation and charge-carrier transport. Furthermore, we find that the NCBA as third component materials can reduce charge-carrier recombination and enhancement of thermal stability in ternary PSCs as well. The results bring new insight into the future development of high-efficiency ternary PSCs.

Enhancement of Inverted Polymer Solar Cells Performances Using Cetyltrimethylammonium-Bromide Modified ZnO.

In this study, the performance and stability of inverted bulk heterojunction (BHJ) polymer solar cells (PSCs) is enhanced by doping zinc oxide (ZnO) with 0–6 wt % cetyltrimethylammonium bromide (CTAB) in the sol-gel ZnO precursor solution. The power conversion efficiency (PCE) of the optimized 3 wt % CTAB-doped ZnO PSCs was increased by 9.07%, compared to a PCE of 7.31% for the pristine ZnO device. The 0–6 wt % CTAB-doped ZnO surface roughness was reduced from 2.6 to 1 nm and the number of surface defects decreased. The X-ray photoelectron spectroscopy binding energies of Zn 2p3/2 (1021.92 eV) and 2p1/2 (1044.99 eV) shifted to 1022.83 and 1045.88 eV, respectively, which is related to strong chemical bonding via bromide ions (Br−) that occupy oxygen vacancies in the ZnO lattice, improving the PCE of PSCs. The concentration of CTAB in ZnO significantly affected the work function of PSC devices; however, excessive CTAB increased the work function of the ZnO layer, resulting from the aggregation of CTAB molecules. In addition, after a 120-hour stability test in the atmosphere with 40% relative humidity, the inverted device based on CTAB-doped ZnO retained 92% of its original PCE and that based on pristine ZnO retained 68% of its original PCE. The obtained results demonstrate that the addition of CTAB into ZnO can dramatically influence the optical, electrical, and morphological properties of ZnO, enhancing the performance and stability of BHJ PSCs.

Efficient Polymer Solar Cells with Alcohol-Soluble Zirconium(IV) Isopropoxide Cathode Buffer Layer

Interfacial materials are essential to the performance and stability of polymer solar cells (PSCs). Herein, solution-processed zirconium(IV) isopropoxide (Zr[OCH(CH3)2]4, ZrIPO) has been employed as an efficient cathode buffer layer between the Al cathode and photoactive layer. The ZrIPO buffer layer is prepared simply via spin-coating its isopropanol solution on the photoactive layer at room temperature without any post-treatment. When using ZrIPO/Al instead of the traditionally used Ca/Al cathode in PSCs, the short-circuit current density (Jsc) is significantly improved and the series resistance of the device is decreased. The power conversion efficiency (PCE) of the P3HT:PCBM-based device with ZrIPO buffer layer reaches 4.47% under the illumination of AM1.5G, 100 mW/cm2. A better performance with PCE of 8.07% is achieved when a low bandgap polymer PBDTBDD is selected as donor material. The results indicate that ZrIPO is a promising electron collection material as a substitute of the traditional low-work-function cathode for high performance PSCs.

Bispentafluorophenyl-Containing Additive: Enhancing Efficiency and Morphological Stability of Polymer Solar Cells via Hand-Grabbing-Like Supramolecular Pentafluorophenyl-Fullerene Interactions.

A new class of additive materials bis(pentafluorophenyl) diesters (BFEs) where the two pentafluorophenyl (C6F5) moieties are attached at the both ends of a linear aliphatic chain with tunable tether lengths (BF5, BF7, and BF13) were designed and synthesized. In the presence of BF7 to restrict the migration of fullerene by hand-grabbing-like supramolecular interactions induced between the C6F5 groups and the surface of fullerene, the P3HT:PC61BM:BF7 device showed stable device characteristics after thermal heating at 150 °C for 25 h. The morphologies of the active layers were systematically investigated by optical microscopy, grazing-incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy. The tether length between the two C6F5 groups plays a pivotal role in controlling the intermolecular attractions. BF13 with a long and flexible tether might form a BF13-fullerene sandwich complex that fails to prevent fullerene's movement and aggregation, while BF5 with too short tether length decreases the possibility of interactions between the C6F5 groups and the fullerenes. BF7 with the optimal tether length has the best ability to stabilize the morphology. In sharp contrast, the nonfluorinated BP7 analogue without C6F5-C60 physical interactions does not have the capability of morphological stabilization, unambiguously revealing the necessity of the C6F5 group. Most importantly, the function of BF7 can be also applied to the high-performance PffBT4BT-2OD:PC71BM system, which exhibited an original PCE of 8.80%. After thermal heating at 85 °C for 200 h, the efficiency of the PffBT4BT-2OD:PC71BM:BF7 device only decreased slightly to 7.73%, maintaining 88% of its original efficiency. To the best of our knowledge, this is the first time that the thermal-driven morphological evolution of the high-performance PffBT4BT-2OD polymer has been investigated, and its morphological stability in the inverted device can be successfully preserved by the incorporation of BF7. This research also demonstrates that BF7 is not only effective with PC61BM but also to PC71BM.

Improved longtime stability of highly efficient polymer solar cells by accurately self-formed metal oxide interlayer at metal electrode

Al as a cheap and air-stable metal material has been widely applied to polymer solar cells (PSCs) as an efficient electrode. However, there are few care whether Al is a right electrode in PSCs for longtime stability. The inverted PSCs with the structure of ITO/ZnO/PTB7-Th:PC71BM/MoO3/Metal electrode were fabricated and the performance and stability of inverted PSCs with Al and AgAl electrodes were investigated. PSCs with AgAl electrode got the highest PCE value of 9.3% without aging. While the PCE of PSCs with Al electrode can be gradually improved and reach the highest value of 7.8% after aging for 36h, which is attributed to the formation of AlOx interlayer at the interface of MoO3/Al. PSCs with AgAl electrode still retained 69% of the initial PCE value and got 6.6% of PCE aging for 796days, showing amazing stability. However, PSCs with Al electrode was dropped to 3.7% of PCE aging for 796days due to the continuously increased thickness of AlOx interlayer, which can greatly increase the series resistance of cells. PSCs with AgAl electrode can be further improved and reach 10.2% of PCE using AZO (Al doped ZnO) instead of ZnO and show better UV-light resistance. The enhanced stability of PSCs with AgAl electrode is attributed to the dense and limited thick AlOx interlayer self-formed at the MoO3/AgAl interface due to the low content of Al. Our results demonstrated that Ag alloy electrode such as AgAl is a good strategy to accurately control the thickness of the metal oxidation interlayer, which can overcome the disadvantage of Al electrode and greatly improve the longtime stability of devices.

Organic Photovoltaics: Self‐Organization of Polymer Additive, Poly(2‐vinylpyridine) via One‐Step Solution Processing to Enhance the Efficiency and Stability of Polymer Solar Cells (Adv. Energy Mater. 17/2017)

Organic Photovoltaics: Self‐Organization of Polymer Additive, Poly(2‐vinylpyridine) via One‐Step Solution Processing to Enhance the Efficiency and Stability of Polymer Solar Cells (Adv. Energy Mater. 17/2017)