Porphyrin-based donor with asymmetric ending groups enables 16.31% efficiency for ternary all-small-molecule organic solar cells

A great attention has been aroused by all-small-molecule organic solar cells (ASM OSCs), thanks to characteristics of small molecules such as well-defined chemical structure and excellent reproducibility between batches. However, it is such a challenge to balance the aggregation behaviors of small molecules, which causes hardship for morphology optimizing of active layers, limiting further efficiency developing for ASM OSCs. Recently, the asymmetric ending group strategy has been employed in non-fullerene acceptors (NFAs) and gained great success. Herein, enlightened by the asymmetric NFAs molecule design, two asymmetric and symmetric small molecule donors, Por-DPP-TR and PTR, were synthesized. Compared to PTR, Por-DPP-TR displays an enlarged dipole moment and enhanced crystallization property. In binary OSCs, contributing to the improved film morphology, Por-DPP-TR:6TIC-based device performed an efficiency of 13.28%. Moreover, ternary ASM OSCs were constructed by employing an isogenous porphyrin-based donor, ZnP-TSEH, and an efficiency of 16.31% was obtained thanks to the further improved carrier transfer properties as well as the well-tuned morphology of obvious bi-continuous network. As far as we know, 16.31% ranks as one of the highest PCEs for ASM OSCs.