Exceeding 14% Efficiency for Solution-Processed Tandem Organic Solar Cells Combining Fullerene- and Nonfullerene-Based Subcells with Complementary Absorption

For a highly efficient tandem organic solar cell, it is important for the subcells to minimize the absorption overlap and generate high and balanced currents. Considering the strong absorption and high external quantum efficiency at the short wavelength, developing a highly efficient blend system with a wide-bandgap (WBG) polymer as the donor and a fullerene derivative as the acceptor in the front cell would be an effective strategy. However, it is a challenge to obtain a high short-current density (J_sc) for this blend system. Here, we develop a WBG polymer (PBD1) with an optical bandgap of 1.88 eV. The PBD1:PC₇₁BM blend system with a thickness of 230 nm achieves a power conversion efficiency (PCE) of 9.8% with a high J_sc of 14.6 mA cm^-2. When tandem devices are fabricated with PBD1:PC₇₁BM in the front cell, a PCE of 14.2% with a high J_sc of 12.3 mA cm^-2 is achieved.