Rational Organic Subcell Engineering Enables Efficient Organic-Perovskite Tandem Solar Cells

Organic subcells are an essential component of organic-perovskite tandem solar cells, yet current choices are limited to those with low open-circuit voltages (VOCs) and efficiencies. By designing and synthesizing benzo[d][1,2,3]triazole-substituted acceptors, LBz-F and LBz-Cl, which exhibit shallower frontier orbital energy levels and narrower optical bandgaps than the typical nonfullerene acceptor L8-BO, we overcome this limitation. LBz-F and LBz-Cl can form alloys with L8-BO in the active layer, broadening the absorption, optimizing charge carrier dynamics, and reducing energy losses of the devices, which results in improved short-circuit currents and fill factors without compromising a high VOC in the organic subcell. By combining PM6:L8-BO:LBz-F as the back cell with a wide bandgap (1.72 eV) perovskite front cell, efficiencies of 22.11% and 20.18% with high VOCs approaching 2.1 V are achieved for small and large area tandem devices, respectively, highlighting the effectiveness of rational organic subcell engineering for efficient, large-area organic-perovskite tandem solar cells.