Suppressing phase segregation and nonradiative losses by a multifunctional cross-linker for high-performance all-perovskite tandem solar cells

Abstract

The tunable bandgaps and facile fabrication of metal halide perovskites make them attractive for tandem solar cells. One of the main bottlenecks to achieve high-performance and stable perovskite-based tandems is the notorious light-induced phase segregation of wide bandgap (WBG) I/Br mixed perovskites in the front subcells. Herein, we find that cross-linked network polymers are effective at suppressing the light-induced phase segregation by passivating the defects and alleviating strain within the perovskite films, compared to the counterparts of small molecules and regular chain polymers. A co-polymerization strategy is employed to construct functional groups on the cross-linked polymers, which further reduces defects and increases the light/thermal stability of WBG perovskites. The as-fabricated WBG perovskite solar cells (PSCs) deliver a certified open-circuit voltage (VOC) of 1.37 V with a 1.77 eV perovskite absorber. The VOC deficit is only 0.40 V, which is among the lowest values for certified WBG PSCs. Also, this strategy enables the fabrication of efficient 2-terminal all-perovskite tandem solar cells with an efficiency of 28.3% with VOC of 2.17 V. The tandem device retains 80% of its initial efficiency after 520 hours of operation at maximum power point.