Lead-Free Perovskite Solar Cells with Efficiencies Reaching 8.29% Based on Single-Crystalline Precursor Solutions

Tin-based perovskite solar cells, with more consummate optical bandgaps, low exciton binding energies, higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a PCE extra 23.6%. The major challenges for Sn-based research are significantly lower open-circuit voltage, poor reproducibility, and environmental instability issues. It has been identified that the oxidation processes take place mainly during preparation of precursor solutions and fabrication of films as the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal resolving and recrystallization technology to suppress the oxidation processes. As a result, PCE of 8.29% (active area of 0.01 cm2) and obtained a PCE of 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of the lead-free perovskite solar cell research.