High-Efficiency Low-Lead Perovskite Photovoltaics Approaching 20% Enabled by a Vacuum-Drying Strategy.

Lead-tin mixed perovskites are excellent photovoltaic materials that can be used in single- or multi-junction perovskite solar cells (PSCs). However, most high-performance Pb-Sn mixed PSCs reported to date are still Pb-dominant. It is highly demanding to develop environmentally friendly low-lead PSCs, but the poor film quality caused by the uncontrollable crystallization kinetics has been hindering the efficiency improvement of low-lead PSCs. Here, a vacuum-drying strategy in the two-step method to fabricate low-lead PSCs (FAPb 0.3 Sn 0.7 I 3 ) with an impressive efficiency of 19.67% is employed. The vacuum treatment induces the formation of low crystalline Pb 0.3 Sn 0.7 I 2 films containing less solvent, thus facilitating the subsequent FAI penetration and suppressing pinholes. Compared with the conventional one-step method, the two-step fabricated low-lead perovskite films with the vacuum-drying treatment exhibit a larger grain size, lower trap density, and weaker recombination loss, thus giving rise to a record-high efficiency near 20% with better thermal stability.