In this study, ferrocenedicarboxylic acid (FDA) has been introduced between an ITO electrode and ZnO interlayer to improve the performance of inverted polymer solar cells. The highest power conversion efficiency (PCE) of 9.06% is achieved among the measurements. Besides, the average PCE of FDA/ZnO based devices is observed with 11.9% enhancement (8.73% vs. 7.80%) compared to ZnO-only devices. Electrical characterization, surface morphology, wetting properties, as well as exciton generation rate and dissociation probability were investigated to understand the impact of FDA insertion on the interfacial properties. It was found that exciton dissociation efficiency and charge collection efficiency were significantly improved after inserting FDA, while the surface morphology, average roughness and water contact angle of the ZnO film were not changed. It was thought that FDA connected to the ITO electrode and ZnO film because of its carboxyl groups, which lead to a compact interfacial contact and reduced charge recombination. In addition, the devices based on the FDA/ZnO interlayers displayed improved stability in the argon-filled glove box without any encapsulation for about 1000 h compared to the ZnO-only devices. This study provides a new idea to introduce materials with functional groups between ITO/metal oxides interfaces to achieve more efficient charge collection and device performance.

•A simple chlorobenzene vapor assistant annealing (CB VAA) method has been developed for the first time to produce high quality perovskite films.•It was found that this method had a positive effect on the interfacial contact between perovskite and PCBM.•Planar heterojunction perovskite solar cells produced by this method possessed enhanced Jsc, PCE with reduced hysteresis.•Various measurements were conducted to investigate the influence of CB VAA method on perovskite films, interface properties as well as perovskite solar cells.In this study, chlorobenzene (CB) vapor assistant annealing (VAA) method is employed to make high quality perovskite films and produce high efficiency CH3NH3PbI3-xClx perovskite solar cells. The perovskite films made by this method present several advantages such as increased crystallinity, large grain size and reduced crystal boundaries compared with those prepared by thermal annealing (TA) method, which is beneficial to charge dissociation and transport in hybrid photovoltaic device. In addition, it is found that the CB VAA method could improve the surface property of perovskite film, resulting in a preferable coverage of PCBM layer and a better interfacial contact between perovskite film and upper PCBM film. Consequently, the short circuit current density (Jsc) of the devices is significantly increased, yielding a high efficiency of 14.79% and an average efficiency of 13.40%, which is 13% higher than that of thermal annealed ones. This work not only put forward a simple and efficient approach to prepare highly efficient perovskite solar cells but also provide a new idea to improve the morphology and interfacial contact in one integration step.Chlorobenzene(CB) vapor assistant annealing process was utilized as a simple and effective method to produce perovskite films in high quality. It was also found that the spreadability of PCBM on perovskite layer could be improved through this procedure at the same time. So, enhanced Jsc, PCE as well as a reduced hysteresis were obtained in the photovoltaic devices.

Organic–inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Here, for the first time, graphdiyne (GD), a novel two dimension carbon material, is doped into PCBM layer of perovskite solar cell with an inverted structure (ITO/PEDOT:PSS/CH3NH3PbI3–xClx/PCBM:GD/C60/Al) to improve the electron transport. The optimized PCE of 14.8% was achieved. Also, an average power conversion efficiency (PCE) of PCBM:GD-based devices was observed with 28.7% enhancement (13.9% vs 10.8%) compared to that of pure PCBM-based ones. According to scanning electron microscopy, conductive atomic force microscopy, space charge limited current, and photoluminescence quenching measurements, the enhanced current density and fill factor of PCBM:GD-based devices were ascribed to the better coverage on the perovskite layer, improved electrical conductivity, strong electron mobility, and efficient charge extraction. Small hysteresis and stable power output under working condition (14.4%) have also been demonstrated for PCBM:GD based devices. The enhanced device performances indicated the improvement of film conductivity and interfacial coverage based on GD doping which brought the high PCE of the devices and the data repeatability. In this work, GD demonstrates its great potential for applications in photovoltaic field owing to its networks with delocalized π-systems and unique conductivity advantage.

ZnO nanofilm as a cathode buffer layer has surface defects due to the aggregations of ZnO nanoparticles, leading to poor device performance of organic solar cells. In this paper, we report the ZnO nanoparticles aggregations in solution can be controlled by adjusting the solvents ratios (chloroform vs methanol). These aggregations could influence the morphology of ZnO film. Therefore, compact and homogeneous ZnO film can be obtained to help achieve a preferable power conversion efficiency of 8.54% in inverted organic solar cells. This improvement is attributed to the decreased leakage current and the increased electron-collecting efficiency as well as the improved interface contact with the active layer. In addition, we find the enhanced maximum exciton generation rate and exciton dissociation probability lead to the improvement of device performance due to the preferable ZnO dispersion. Compared to other methods of ZnO nanofilm fabrication, it is the more convenient, moderate, and effective to get a preferable ZnO buffer layer for high-efficiency organic solar cells.Keywords: aggregations of ZnO nanoparticles; cathode buffer layer; inverted organic solar cells; mixed solvents

We reported the favorable cathode buffer layer based on a blend of ZnO nanoparticles (NPs) and TiO2 nanorods (NRs) applied to inverted solar cells. In addition to the high optical transmittance, the resultant blend film gave a relatively dense film with lower roughness than that of the respective single-component film. This improved the interface contact between the buffer layer and photoactive layer and therefore reduced the contact resistance and leakage current. Moreover, the combination of NRs and NPs increased the efficiency of electron transport and collection by providing both a direct path for electron transport from TiO2 NRs and a large contact area between ZnO NPs and the active layer. Consequently, both the short-circuit current density (Jsc) and fill factor (FF) in the device were improved, leading to an improvement of the device performance. The best power conversion efficiency (PCE) based on the blend film as the buffer layer reached 8.82%, which was preferable to those of a single ZnO NP film (7.76%) and a TiO2 NR-based device (7.66%).Keywords: blend film; cathode buffer layer; inverted solar cells; TiO2 nanorods; ZnO nanoparticles;

We reported a significant improvement in the efficiency of organic solar cells by introducing hybrid TiO2:1,10-phenanthroline as a cathode buffer layer. The devices based on polymer thieno[3,4-b]thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) with hybrid buffer layer exhibited an average power conversion efficiency (PCE) as high as 8.02%, accounting for 20.8% enhancement compared with the TiO2 based devices. The cathode modification function of this hybrid material could also be extended to the poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) system. We anticipate that this study will stimulate further research on hybrid materials to achieve more efficient charge collection and device performance.Keywords: 1,10-phenanthroline; hybrid buffer layer; inverted OSC; TiO2;

Highly efficient organic solar cells were successfully demonstrated by incorporating a solution-processed cesium stearate between the photoactive layer and metal cathode as a novel cathode interfacial layer. The analysis of surface potential change indicated the existence of an interfacial dipole between the photoactive layer and metal electrode, which was responsible for the power conversion efficiency (PCE) enhancement of devices. The significant improvement in the device performance and the simple preparation method by solution processing suggested a promising and practical pathway to improve the efficiency of the organic solar cells.Keywords: cesium stearate; efficiency; interfacial layer; organic solar cells; solution-processed;

We used cesium stearate (CsSt) to modify the interface of the electron-extracting contact in inverted organic solar cells. Surface microstructure, optical properties, and electrical characterization as well as exciton generation rate and dissociation probability were investigated to understand the impact of CsSt on the interface contact. The results indicated that by incorporation of CsSt, the surface morphology and energy level as well as conductivity of a zinc oxide (ZnO) film were improved. On the basis of the above properties, highly efficient inverted organic solar cells have been demonstrated by using a ZnO nanoparticle film and CsSt stacked bilayer structure as the cathode interfacial layer. The insertion of a CsSt layer between the ZnO film and active layer improved the electron extraction efficiency, and a high power conversion efficiency (PCE) of 8.69% was achieved. The PCE was improved by 20% as compared to the reference device using a ZnO-only electron extraction layer.Keywords: Cesium stearate; Exciton dissociation; Interfacial modification; Organic solar cells

•ZnO nanoparticles (NPs) modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) are introduced in inverted polymer solar cells as cathode buffer layer.•The morphology improvement of the PyC60/ZnO bilayer film contributes to reducing series loss and interfacial charge recombination.•The preferable interfacial contact between ZnO/PyC60 bilayer film and photoactive layer lowers electron injection barrier between photoactive layer and ZnO film.•The ZnO/PyC60 device based on a blend of PTB7:PC71BM as photoactive layer exhibits higher FF of 72.5% and PCE of 8.76%, respectively.In this paper, we reported that ZnO nanoparticles (NPs) film modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) was used as cathode buffer layer in inverted polymer solar cells. The resultant device with a blend of PTB7:PC71BM as photoactive materials exhibited an open-circuit voltage (Voc) of 0.753 V, a short-circuit current (Jsc) of 16.04 mA cm−2, a fill factor (FF) of 72.5%, and an overall power conversion efficiency (PCE) of 8.76%. It was higher than the control devices based on sole ZnO NPs film or ZnO: PyC60 hybrid film as cathode buffer layer. It was found that the morphology improvement of ZnO/PyC60 film contributed to reducing series loss and interfacial charge recombination. In addition, it improved the interfacial contact with photoactive layer. The results increased electron injection and collection efficiency, and improved FF.ZnO nanoparticles (NPs) modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) are introduced in inverted polymer solar cells as cathode buffer layer. The morphology improvement of the ZnO/PyC60 bilayer film contributes to reducing series loss and interfacial charge recombination. Consequently, the resultant inverted solar cells exhibit an overall power conversion efficiency (PCE) of 8.76%.

•We have developed a facile sol–gel method to synthesize CuS NCs.•The pyridine capped CuS NCs can be used directly as interfacial layer without ligand-exchange.•The hydrophilic CuS NCs can be exchanged with OAm and OA rapidly at room temperature and present hydrophobic characteristic.•The CuS NCs possess the superior interfacial property and can be processed in lower temperature than other metal oxide.CuS NCs were synthesized via a facile sol–gel method without post-thermal treatment. The as-prepared CuS NCs were analyzed and confirmed by XRD, HR-TEM, EDS and XPS as hexagonal covellite CuS. The average diameter of the samples was about 3 nm with narrow size distribution. CuS NCs can form a thin and smooth film without ligand-exchange that can be used as hole transport layer in organic solar cell. These hydrophilic CuS NCs with pyridine ligands can be exchanged with OAm and OA rapidly at room temperature and present hydrophobic characteristic, resulting in forming oil-soluble CuS NCs. This makes it possible tuning the surface property of CuS NCs and has the potential application for different fields.

•We have developed an in situ method to prepare MoO3 thin film.•The composition and microstructure of the thin film were studied.•The MoO3 film possessed columnar morphology.•The MoO3 film was proved to have superior property in organic photovoltaics.Columnar MoO3 in situ growth prepared from direct converting soluble Mo-containing precursor during active layer thermal annealing was utilized as anode buffer layer to fabricate organic bulk heterojunction photovoltaics. The columnar morphology could improve the interface contact between active layer and buffer layer. The structure and phase of in situ formed MoO3 were studied by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We demonstrated that the organic photovoltaic devices based on P3HT:PC61BM using in situ formed columnar MoO3 as anode buffer layer presented a high open-circuit voltage and fill factor leading to an efficiency of 3.92%, which is higher than the controlled PEDOT:PSS-based devices.Graphical abstractColumnar MoO3 in situ growth prepared from direct converting soluble Mo-containing precursor during active layer annealing in organic photovoltaic device fabrication was utilized as anode buffer layer which simultaneously increase short circuit current and fill factor, resulting in enhanced device efficiency.