Efficient n-type dopants with extremely low doping ratios for high performance inverted perovskite solar cells

Abstract

N-type doping is an effective way to increase the short circuit current (J_sc) of perovskite solar cells (PSCs), thus enhancing their power conversion efficiency (PCE). However, the largely decreased open circuit voltage (V_oc) and fill factor (FF) are always drawbacks in traditional n-type doping. Moreover, efficient n-type dopants are rare to date and it is therefore desirable and urgent to develop new n-type dopants with a better n-type doping ability for high performance PSCs. Here, a series of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole derivatives have been designed and synthesized, which provides a successful case of tailoring the doping ability of n-type dopants. It has been demonstrated that with a stronger n-type dopant, an extremely low doping ratio would be sufficient to boost the J_sc, while enhancing the FF and minimizing the V_oc loss. By using the strongest n-type dopant, a PCE of over 18% is achieved in an inverted PSC with a remarkably low doping ratio of 0.05% by weight.