Simplified fabrication of high-performance organic solar cells through the design of self-assembling hole-transport molecules

The commercialization of organic solar cells (OSCs) encompasses overcoming hurdles related to efficiency, stability, cost, and complexity of device fabrication techniques. The elaborate sequential deposition (SD) process for fabricating charge-transport and photoactive layers stands out as a critical challenge. In this study, we synthesized a series of self-assembling hole-transport molecules, namely, BPC-M, BPC-Ph, and BPC-F, to investigate the mechanism within self-assembling deposition (SAD). The synthesized molecules in SAD-processed cells exhibit significantly varied photovoltaic performance. Notably, BPC-M achieves a superior power conversion efficiency of 19.3% in SAD-processed PBDB-TF:eC9 cells. However, cells incorporating BPC-F show significant performance degradation. It is demonstrated that the thermodynamic forces driven by surface free energy, coupled with intermolecular interactions, are pivotal in dictating the self-assembly efficiency. This determines the quality of the self-assembled layer and the residual molecule in the active layer. This study simplifies OSC fabrication and offers a promising approach for the industrialization of OSCs.