Cross-linked hole transport layers for high-efficiency perovskite tandem solar cells

Perovskite tandem solar cells have recently received extensive attention due to their promise of achieving power conversion efficiency (PCE) beyond the limits of single-junction cells. However, their performance is still largely constrained by the wide-bandgap perovskite solar cells which show considerable open-circuit voltage (VOC) losses. Here, we increase the VOC and PCE of wide-bandgap perovskite solar cells by changing the hole transport layer (HTL) from commonly used poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) to in-situ cross-linked small molecule N4,N4′-di(naphthalen-1-yl)-N4,N4′-bis(4-vinylphenyl) biphenyl-4,4′-diamine (VNPB). The stronger interaction and lower trap density at the VNPB/perovskite interface improve the PCE and stability of wide-bandgap perovskite solar cells. By using the cross-linked HTL for front wide-bandgap subcells, PCEs of 24.9% and 25.4% have been achieved in perovskite/perovskite and perovskite/silicon tandem solar cells, respectively. The results demonstrate that cross-linkable small molecules are promising for high-efficiency and cost-effective perovskite tandem photovoltaic devices.