Effect of side chain modification on edge‐on oriented dithienobenzodithiophene‐based non‐fullerene acceptors for organic solar cells

Abstract

AbstractTwo non‐fullerene acceptors (NFAs), DTBDT‐ICN and DTBDT‐SEH, based on dithienobenzodithiophene (DTBDT) and a 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene) malononitrile (IC) with different side chains of alkylthienyl and alkylthio‐thienyl, respectively, were designed and used as electron acceptors in organic solar cells (OSCs). Both NFAs provide suitable energy level configurations that ensure efficient charge transfer with the donor polymer PBDB‐T, as confirmed by significant photoluminescence reduction in the blend films. However, due to the high planarity together with strong π‐π stacking interactions, the DTBDT‐ICN presented significant aggregation and phase separation in the blend films, leading to suboptimal charge generation. In addition, grazing incidence wide‐angle x‐ray scattering measurements revealed a predominance of edge‐on molecular orientations, which are unfavorable for vertical charge transport. On the other hand, DTBDT‐SEH exhibited less pronounced molecular aggregation and edge‐on orientation properties compared to DTBDT‐ICN, resulting in improved carrier mobility (μe of 3.86 × 10−6 compared to 7.59 × 10−7) and mitigated recombination losses (1.19 kT/q compared to 1.21 kT/q) in OSC devices. The improved morphological features of PBDB‐T:DTBDT‐SEH led to a high power conversion efficiency of 3.31%, which is three times higher than that of PBDB‐T:DTBDT‐ICN‐based devices (1.55%). Furthermore, paired with the high performance polymer PM6, PM6:DTBDT‐SEH demonstrated an enhanced efficiency, reaching 7.03%.