Impact of Electrostatic Interaction on Bulk Morphology in Efficient Donor-Acceptor Photovoltaic Blends

Bulk heterojunctions comprising mixed donor (D) and acceptor (A) materials have proven to be the most efficient device structures for organic photovoltaic (OPV) cells. The bulk morphology of such cells plays a key role in charge generation, recombination, and transport, thus determining the device performance. Although numerous studies have discussed the morphology-performance relationship of these cells, the method of designing OPV materials with the desired morphology remains unclear. Herein, guided by molecular electrostatic potential distributions, we have established a connection between the chemical structure and bulk morphology. We show that the molecular orientation at the D-A interface and the domain purity in the blend can be effectively modulated by modifying the functional groups. Enhancing the D-A interaction is beneficial for charge generation. However, the resulting low domain purity and increased charge transfer ratio in its hybridization with the local excitation states lead to severe charge recombination. Fine-tuning the bulk morphology can give balanced charge generation and recombination, which is crucial for further boosting the efficiency of the OPV cells.

Automated summary

The morphology of bulk heterojunctions in organic photovoltaic cells is crucial for charge generation, recombination, and transport, ultimately determining device performance. Enhancing the D-A interaction can benefit charge generation, but it may lead to severe charge recombination if domain purity is compromised. Fine-tuning the bulk morphology by modifying functional groups is essential for balancing charge generation and recombination in order to boost the efficiency of OPV cells.