The new era for organic solar cells: polymer acceptors

Organic solar cells (OSCs) have made fast advance with prominent power conversion efficiencies (PCEs) achieved in non-fullerene OSCs in recent years [1]. Among various types of OSCs, all-polymer solar cells (APSCs) consisting of a polymer donor and a polymer acceptor are promising power sources for portable and wearable electronics due to their intrinsic advantages in device stability and mechanical flexibility [2]. Duan group [3] demonstrated an APSC that maintained 97% of its initial PCE after continuous heating at 65 °C for 300 h, which is much superior to the small molecular acceptor-based OSCs. Kim group [4] compared the mechanical properties of the active layers of APSCs and fullerene acceptor-based OSCs containing the same polymer donor. It was demonstrated that the elongation at the break and toughness of all-polymer blend were 60 and 470 times, respectively, higher than those of polymer:fullerene blend. These advantageous mechanical properties are desirable for practical application of OSCs [5,6]. However, the development of APSCs lags much behind that of small molecular acceptor-based OSCs. In particular, there is a big gap in PCE between APSCs and small molecular acceptor-based OSCs, which is mainly caused by the lack of polymer acceptors with desirable optoelectronic properties and difficulties in morphology control of the active layer.