High-Performance Rigid and Flexible Perovskite Solar Cells with Low-Temperature Solution-Processable Binary Metal Oxide Hole-Transporting Materials

To achieve high performance in perovskite solar cells (PSC), the hole-transporting layer (HTL) is very important. In this work, we introduce a novel copper-chromium binary metal oxide as the hole-transporting material for PSC application. This low temperature solution-process HTL enables high performance PSC. The energy levels and phase compositions of the binary metal oxide can be modulated with different copper acetylacetonate (y)/chromium acetylacetonate (z) volume ratios in the reacting solution precursors. X-ray diffraction and X-ray photoelectron spectroscopy show that both mono CuyO(z = 0) or CrzO(y = 0) and binary CuCrO2 and CuCr2O4 phases can be formed. The Cr-terminated polar CuCrO2 component leads to films with superior wettability and compatibility with perovskite precursor solution, while the formation of high coverage uniform perovskite films is favorable for device fabrication. Unlike copper oxides, the copper-chromium binary metal oxide films have wide band gaps of around 3.1 eV, as well as suitable energy levels for both electron-blocking and hole-transporting. As a result, PSCs with this low-temperature solution processed copper-chromium binary metal oxide HTL have achieved high PCE of 17.19% on glass and 15.53% on flexible PET substrates, which is a significant enhancement over mono-metal oxide based devices.