Ultrafast Dynamics Group
Frédéric Laquai's Group

Page 07/17/2018 16:19:55

Wide‐Bandgap Small Molecular Acceptors Based on a Weak Electron‐Withdrawing Moiety for Efficient Polymer Solar Cells

Y. Gong, Z. Kan, W. Xu, Y. Wang, S.H. AlShammari, F. Laquai, W.Y. Lai, W. Huang
non‐fullerene acceptors, organic photovoltaics, polymer solar cells, small molecular acceptors, wide‐bandgap acceptors
​Narrow‐bandgap small molecular acceptors (SMAs) with absorption extending into the near‐infrared spectral region such as ITIC derivatives is widely investigated, while the development of their wide‐bandgap counterparts remains largely unexplored. Wide‐bandgap non‐fullerene acceptors (NFAs) is highly desirable and beneficial for constructing efficient device layouts such as ternary blend and tandem solar cells that require multiple light‐harvesting materials with different regions of absorption. In this contribution, we present the design and synthesis of two wide‐bandgap SMAs (IDT‐TBA and IDDT‐TBA), consisting of a weak electron‐withdrawing moiety (1,3‐diethyl‐2‐thiobarbituric acid, TBA). Compared to ITIC, this molecular design strategy results in energetically down‐shifted HOMO levels and hence much enlarged bandgaps of 1.91 eV for IDT‐TBA and 1.78 eV for IDDT‐TBA, respectively. Further photovoltaic performance evaluation demonstrates power conversion efficiencies (PCEs) of 6.5% for IDT‐TBA and 7.5% for IDDT‐TBA, respectively, with using PBDB‐T as the electron donor polymers. In addition, time‐delay collection field (TDCF) experiments suggested that both IDT‐TBA and IDDT‐TBA based cells exhibited field‐independent charge generation with external charge generation efficiencies exceeding 90%, implying negligible geminate recombination losses. The results demonstrate that TBA units are promising and attractive building blocks as weak electron‐withdrawing acceptors to construct wide‐bandgap high‐efficiency SMAs for efficient organic photovoltaic devices.