Novel cathode buffer layer enabling over 21.6%/20.9% efficiency in wide bandgap/inorganic perovskite solar cells

Different types of hybrid organic/inorganic halide perovskite solar cells (PSCs) have attracted extensive research attention and showed extremely considerable practical application potential in current energy field, for instance, wide bandgap (WBG) PSCs are widely used in fabricating high-efficiency tandem devices, while inorganic perovskite solar cells (IPSCs) had been sought after by researchers due to its excellent thermal stability. However, either WBG PSCs or IPSCs were severely influenced by the carrier extraction and transport between the electron transfer layer and anode/cathode. On this basis, an in-situ oxygen plasma treated Ti doped ZnO film named TZO (O) was used as cathode buffer layer to regulate the energy-level alignment between the SnO2 layer and ITO electrode, optimize the crystal quality of perovskite and passivate perovskite defects through providing superior SnO2 film. It is found that the more suitable energy levels for the interlamination availably polished up carrier transport effect to a great extent, which could be seen in steady-state and time-resolved photoluminescence spectra, in addition to this, the perovskite film covered on TZO (O)/ SnO2 demonstrated larger perovskite crystals and less surface defects. As a consequence, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈ 1.66 eV up to 21.62%, and the efficiency of CsPbI2.85Br0.15 IPSCs is enhanced from 19.21% to 20.92%. Moreover, the unencapsulated TZO (O)-treated wide bandgap PSCs shows enhanced stability, retaining 89.47% of its initial efficiency after 1000 h in a N2 filled environment, while the unencapsulated IPSCs-based TZO (O) still remains 83.77% of its initial efficiency under continuous illumination in air for 325 h. This work exhibited that the buffer layer TZO (O) is a promising interfacial modification material for both n-i-p type wide bandgap PSCs and IPSCs.