Sol-Gel Prepared Spinel HTLs for Assembling 20% Efficiency Perovskite Solar Cell in Air Without Using Anti-Solvent and Toxic Solvent

Low-temperature sol-gel prepared ZnCo₂O₄ spinel-based thin films are developed as high-performance hole transporting layer (HTL) for coating perovskite film (NA-Psk) from the basic MAPbI₃/ACN/CH₃NH₂ solution in air without using anti-solvent. Inverted PSC based on 2 mole% (vs Zn) Cu²⁺ doped ZnCo₂O₄ (2%Cu@ZnCo₂O₄) HTL and NA-Psk absorber exhibit the maximum power conversion efficiency (PCE) of 20.0% with no current hysteresis while the cell based on ZnCo₂O₄ and PEDOT:PSS HTL (using NA-Psk absorber) achieves the PCE of 15.79% and 12.3% with a current hysteresis index of 9.8% and 32.4%, respectively. Without encapsulation, PSCs based on 2%Cu@ZnCo₂O₄, ZnCo₂O₄, and PEDOT:PSS HTLs maintain 90%, 77%, and 12%, respectively of the original efficiency by standing in ambient atmosphere (temperature: 20–25 °C, RH:30%–40%) for 1800 h. Large area (10 cm × 10 cm substrate) perovskite mini-module (PSM) with PCE over 15% is also demonstrated by using sol-gel prepared 2%Cu@ZnCo₂O₄ HTL. The poor photovoltaic performance of PEDOT:PSS HTL is due to the basic MAPbI₃/ACN/CH₃NH₂ solution will deprotonate the acidic PEDOT:PSS to reduce its conductivity whereas ZnCo₂O₄ HTL are not affected by basic perovskite precursor solution.