Overcoming efficiency loss of large-area all-polymer solar cells via asymmetric alkyl side-chain engineering of naphthalene diimide-based n-type polymer

Abstract

All-polymer solar cells (all-PSCs) are considered to be the priority in the commercialization process of organic photovoltaics due to their excellent stability. However, it faces the key challenge of device area enlargement leading to degradation of photovoltaic performance because of the significantly different shear forces at center and edges of the substrate. In this work, we designed and synthesized a NDI-based n-type polymer P(NDIHDDT-T2) with asymmetric alkyl side-chain to overcome this key challenge. All-PSCs based on P(NDIHDDT-T2) showed impressive high power conversion efficiency (PCE) of 11.2% for 0.04 cm2 device and 10.4% (reduced by about 7%) for 1 cm2 device, respectively, both of which outperformed the 10.7% for 0.04 cm2 device and 9.1% (reduced by about 15%) for 1 cm2 all-PSCs based on P(NDI2OD-T2). To the best of our knowledge, this is the highest PCE achieved for 1 cm2 NDI-based all-PSCs. We analyzed the interrelationship between the lengths of alkyl side-chain, crystalline and aggregation behavior, and photovoltaic performance of 1 cm2 device, which proved the advance of asymmetric alkyl side-chain engineering for constructing high-performance large-area all-PSCs, and may promote the commercialization process of all-PSCs.