Enhanced efficiency in two-terminal all-perovskite tandem solar cells via binary functional high polymer doping strategy

An enhanced power conversion efficiency (PCE) of 26.1 % has been achieved in two-terminal (2 T) all-perovskite tandem perovskite solar cells (TPSCs) via the binary functional high polymer doping strategy. By incorporating methylene diphenyl diisocyanate polyurethane (MDI-PU) and PJ71 into the wide bandgap (WBG) and narrow bandgap (NBG) perovskite layers, respectively, the perovskite crystalline quality of them was significantly improved. The optimized PCE of the WBG top cell and NBG bottom cell achieved 17.6 % and 20.9 %, respectively. After continuous dark storage of 150 days in nitrogen-filled glovebox, the PCE of optimized TPSC remained 94.2 % of initial. TPSCs on flexible substrates of polyethylene naphthalate (PEN) and silk-derived substrate (SDS) were also studied. With the binary polymer doping strategy, the PEN-based TPSC achieved a champion PCE of 22.2 %, and exhibited excellent anti-bending ability compared with control. The champion SDS-based TPSC achieved the PCE of 11.6 %, and showed enhanced anti-stretching ability. We demonstrate that strong coordinate bonding formed between the O atom in the carbonyl group of MDI-PU and the Pb2+ ions at the grain boundaries (GBs) in WBG perovskite. For the NBG layer, the S atoms in the thiophene structure of PJ71 interact with the Pb2+ and Sn2+ ions in the NBG perovskite and effectively passivate the GB defects. The study suggests the potential for developing new generation multi-functional optoelectronic polymers to further boost the performance of 2 T all-perovskite TPSCs.