Efficient monolithic all-perovskite tandem solar modules with small cell-to-module derate

All-perovskite tandem solar modules are promising to reduce the cost of photovoltaic systems with their high efficiency and solution fabrication, but their sensitivity to air still imposes a great challenge. Here a hot gas-assisted blading method is developed to accelerate the perovskite solidification, forming compact and thick narrow bandgap (NBG) perovskite films. Adding a reduction agent into NBG films followed by a short period of air exposure and a post-fabrication storage surprisingly increases carrier recombination lifetime and enables laser scribing in ambient conditions without obvious loss of device performance. This combination suppresses tin and iodide oxidation and forms a thin SnO2 layer on the NBG film surface. Monolithic all-perovskite tandem solar modules showed a champion efficiency of 21.6% with a 14.3 cm2 aperture area, corresponding to an active area efficiency of 23.0%. The very small cell-to-module derate of 6.5% demonstrates the advantage of a tandem monolithic structure for solar modules. Scaling up all-perovskite tandem solar modules is challenging due to the degradation of the low-bandgap subcell during processing in ambient conditions. Here Dai et al. devise an additive- and hot gas-assisted blade-coating process that enables modules with 21.6% efficiency over an aperture area of 14.3 cm2.