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, we established a relationship between the molecular structure and the VPS morphology of pseudo-planar heterojunction (PPHJ) OSCs by using molecular surface electrostatic potential (ESP) as a bridge. We revealed the morphological evolution mechanism by studying four binary systems with vary electrostatic potential difference (∆ESP) between donors and acceptors. Our findings manifest that as ∆ESP increases, the active layer is more likely to form a well-mixed phase, while a smaller ∆ESP favors VPS morphology. Interestingly, we also observed that a larger ∆ESP led to enhanced miscibility between donors and acceptors, resulting in higher non-radiative energy losses (ΔE 3 ). Based on these discoveries, we meticulously designed a ternary PPHJ device with an appropriate ∆ESP to obtain better VPS morphology and lower ΔE 3 , and achieve an impressive efficiency of 19.09%. Our work demonstrates that by optimizing the ΔESP, we can not only control the formation of VPS morphology but also reduce energy losses, paving the way to further boost OSC performance. This article is protected by copyright. All rights reserved.