A new polymer donor for efficient polymer solar cells: simultaneously realizing high short-circuit current density and transparency

A polymer donor material with appropriate energy levels and high light-harvesting capability is critical for highly efficient polymer solar cells (PSCs). Especially, it is a challenge to develop polymer donors which can simultaneously achieve both high short-circuit current density (Jsc) and transmittance for semitransparent PSCs. In this work, we designed and synthesized two new conjugated polymers PBT-F and PBT-SF which possess strong absorption features and appropriate energy levels as donor materials for PSCs. By using IT-4F as an acceptor, high Jsc values of over 21 mA cm−2 were obtained for both PBT-F and PBT-SF-based devices, showing promising power conversion efficiencies (PCEs) of 9.14% and 10.51%, respectively. Very importantly, the optimal PBT-SF:IT-4F blend film possesses a thinner thickness (∼80 nm) and high transmittance in the 400–600 nm region. The semitransparent PSCs based on PBT-SF:IT-4F showed an encouraging PCE of 7.76%, with a notable average transmittance of 39% and a high Jsc of 17.48 mA cm−2. These results demonstrate that PBT-SF is a promising polymer donor for high performance opaque and semitransparent PSCs.