Solution-Synthesized Cu2O As a Hole Transport Layer for a ZnO-Based Planar Heterojunction Perovskite Solar Cell Fabricated at Room Temperature

The race towards modern photovoltaic devices necessitates the development of more efficient and stable perovskite solar cells (PSC) at reliable cost. Metal oxides are exploited as better materials for electron and hole transport in PSCs. ZnO has emerged as a better substitute for the TiO2 electron transport layer (ETL) owing to its higher electron mobility, low cost, simple synthesis methodologies and low annealing temperature which facilitates its application on flexible substrates. Most high-performance PSCs using ZnO ETL employ various organic hole transport layers (HTL) such as spiro-OMeTAD, which are high cost, unstable and involves complex fabrication processes. Metal oxide HTLs are commonly fabricated as p type HTL of ZnO-based inverted p-i-n structures of PSC. Cu2O has emerged as a p-type layer for various p-i-n configurations using ETLs such as TiO2 and phenyl c-61 butyric acid methyl ester (PCBM). The application of metal oxides such as Cu2O as the p type top HTL of PSC is considered as complex in fabrication. The work focusses on the fabrication of Cu2O and NiO as the top layer for ZnO n-i-p planar configuration, fluorine-doped tin oxide (FTO)/ZnO/CH3NH3PbI3/Cu2O/Au and (FTO)/ZnO/CH3NH3PbI3/NiO/Au. Moreover, the metal oxides are synthesized by a simple solution synthesis process and used in their pure form without any doping or surface treatments. Different layers were grown using spin coating at room temperature. The fabricated n-i-p structure, FTO/ZnO/CH3NH3PbI3/Cu2O/Au exhibited a stable power conversion efficiency of 6.02% with J(sc) of 12 mA/cm(2), V-oc of 0.76 V and fill factor of 0.63. The performance of this structure was compared with the second structure which showed a power conversion efficiency of 5.02%. Cu2O thus proves to be a reliable inorganic HTL that can be employed for ZnO n-i-p planar configuration.