Tandem organic solar cells with efficiency over 19% via the careful subcell design and optimization

The series-connected tandem device strategy is an effective approach to promote the efficiency of organic solar cells (OSCs) with broadened absorption range and alleviated thermalization and transmission loss. In this article, two nonfullerene acceptors, FBr-ThCl and BTP-4Se, with complementary absorptions covering the range from 300 to 1,000 nm were designed and synthesized for the front and rear cell, respectively. The front cell based on D18:FBr-ThCl exhibited a V-oc of 1.053 V with high external quantum efficiency (EQE) response values ranging from 300 to 740 nm. The rear cell with a ternary active layer PM6:BTP-4Se: F-2F was optimized and afforded the V-oc of 0.840 V and J(sc) of 26.88 mA cm(-2). Subsequently, the tandem device was constructed with a fully solution-processed interconnected layer of ZnO/PEDOT:PSS/PMA, and demonstrated a power conversion efficiency (PCE) of 19.55% with a V-oc of 1.880 V, a J(sc) of 13.25 mA cm(-2) and an FF of 78.47%.