Development of efficient and mechanically stable polymer acceptors for all-polymer solar cells via incorporation of flexible alkyl segments

Abstract

Recently, all-polymer solar cells (all-PSCs) have been in the spotlight for their stretchable and extendable potential to wearable electronics. For practical applications, not only high efficiency but also mechanical robustness of the device is considered as important factors. From this point of view, a technical strategy incorporating a flexible conjugation-break spacer (FCBS) has been reported to achieve mechanically robust and high efficient all-PSCs. The incorporation of FCBS increases both the mechanical properties and photovoltaic performances of all-PSCs by effectively controlling the crystallinity and pre-aggregation of the polymer acceptors ($P_A$s), and achieving an optimal blend morphology with polymer donor. In this study, we report the optimal alkyl linker length point at the $P_A$s. The all-PSC based on PYTS-C2 as a $P_A$ and a polymer donor (PBDB-T) shows a high power conversion efficiency (PCE) of 11.37%, superior mechanical stretchability with a crack onset strain (COS) of 12.39% and toughness of 2.09 $MJ$ $m^{-3}$, which is significantly improved compared to those of devices with the $P_A$s without FCBS (PYT-C0 : PCE = 5.15% and COS = 2.75%) or with the longer length of FCBS (PYTS-C4 : PCE = 3.28%, COS = 0.68%, PYTS-C8 : PCE = 3.17% and COS = 0.45%). These results demonstrate that the incorporation of the proper length of FCBS into the conjugated backbone is highly feasible approach to simultaneously enhance the PCE and stretchability of all-PSCs.