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In this article, we in situ fabricated copper sulfide (CuS) on fluorinated tin oxide (FTO) substrate using a low temperature and low cost hydrothermal method and then organic solar cells (OSCs) were fabricated by using a thin layer of CuS film as hole transporting layer (HTL). Our CuS films, consisting of two-dimensional (2D) intersected hexagonal nanosheets, are stoichiometric and show p-type electrical conductivity, a good transparency and a high hole mobility. The Fermi level, valence and conduction band energies for CuS HTL are characterized in detail through photoelectron spectroscopy studies. The small energy barrier between the valance band of CuS and the HOMO of poly(3-hexylthiophene) (P3HT) and the high hole mobility and electrical conductivity of CuS nanosheet film benefit for the hole transporting. Therefore, CuS HTL to OSCs results in a power conversion efficiency of 3.4% with P3HT and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer, which is a 13.3% increase in performance than devices with a poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) HTL. Therefore, low-cost, environmental friendly and stable CuS is an appropriate choice for hole transporting materials (HTMs) in OSCs. [ABSTRACT FROM AUTHOR]

Abstract: Efficient bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on poly (3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) were fabricated with lithium fluoride (LiF) as electron collecting buffer layer and UV–ozone (UVO) treated molybdenum trioxide (MoO3) as hole collecting buffer layer. LiF is observed to be critical for the device performance, significantly enhancing the fill factor (FF) and the efficiency compared to the device without LiF layer. MoO3 layer is also critical to the device performance, efficiently extracting holes to prevent the exciton quenching and reducing the interfacial resistance because of alignment of energy band. After UVO treatment on MoO3 film, its surface morphology, transmittance and film quality can be improved, therefore, it is beneficial to the performance of the PSCs. The optimal thickness of MoO3 and UVO treatment time on MoO3 was 12nm and 15min, respectively. Based on these optimal parameters, a power conversion efficiency (PCE) of 6.43% was obtained under AM1.5G 100mW/cm2 illumination. [Copyright &y& Elsevier]