Efficient near-infrared harvesting in perovskite-organic tandem solar cells

The broad bandgap tunability of both perovskites and organic semiconductors enables the development of perovskite-organic tandem solar cells with promising theoretical efficiency. However, the certified efficiencies of reported perovskite-organic tandem solar cells remain lower than those of single-junction perovskite solar cells, primarily because of insufficient near-infrared photocurrent in narrow-bandgap organic subcells^1-3. Here we design and synthesize an asymmetric non-fullerene acceptor (NFA), P2EH-1V, featuring a unilateral conjugated π-bridge to reduce the optical bandgap to 1.27 eV while maintaining ideal exciton dissociation and nanomorphology. Transient absorption spectroscopy confirms efficient hole transfer from P2EH-1V to the donor PM6. Devices based on P2EH-1V exhibit reduced non-radiative voltage losses of 0.20 eV without compromising charge-generation efficiency. We achieve a 17.9% efficiency for the organic bottom cell, with a high short-circuit current density (J_sc) of 28.60 mA cm^-2. Furthermore, we minimize interface recombination losses, enabling the perovskite top cell to achieve an impressive open-circuit voltage (V_oc) of 1.37 V and a fill factor (FF) of 85.5%. These advancements result in perovskite-organic tandem solar cells achieving a record efficiency of 26.7% (certified at 26.4%) over an aperture area greater than 1 cm².