Impact of Electrostatic Interaction on Vertical Morphology and Energy Loss in Efficient Pseudo-Planar Heterojunction Organic Solar Cells

Although a suitable vertical phase separation (VPS) morphology is essential for improving charge transport efficiency, reducing charge recombination, and ultimately boosting the efficiency of organic solar cells (OSCs), there is a lack of theoretical guidance on how to achieve the ideal morphology. Herein, a relationship between the molecular structure and the VPS morphology of pseudo-planar heterojunction (PPHJ) OSCs is established by using molecular surface electrostatic potential (ESP) as a bridge. The morphological evolution mechanism is revealed by studying four binary systems with vary electrostatic potential difference ( increment ESP) between donors (Ds) and acceptors (As). The findings manifest that as increment ESP increases, the active layer is more likely to form a well-mixed phase, while a smaller increment ESP favors VPS morphology. Interestingly, it is also observed that a larger increment ESP leads to enhanced miscibility between Ds and As, resulting in higher non-radiative energy losses (Delta E3). Based on these discoveries, a ternary PPHJ device is meticulously designed with an appropriate increment ESP to obtain better VPS morphology and lower Delta E3, and an impressive efficiency of 19.09% is achieved. This work demonstrates that by optimizing the Delta ESP, not only the formation of VPS morphology can be controlled, but also energy losses can be reduced, paving the way to further boost OSC performance. A relationship between the molecular structure and the vertical phase separation (VPS) morphology of PPHJ OSCs by using molecular surface electrostatic potential (ESP) as a bridge is first established. A ternary PPHJ device with an appropriate increment ESP is elaborately constructed to achieve better VPS morphology and lower Delta E3, resulting in impressive efficiency of 19.09%. image