Suppressing Nonradiative Energy Loss in Ternary Organic Solar Cells Through Elaborate Disruption of Planarity of Guest Acceptor

Abstract

The relatively large non-radiative energy loss (ΔEnr) in organic solar cells (OSCs) remains a major obstacle for improving the power conversion efficiency (PCE). Therefore, it is imperative to minimize ΔEnr through rational molecular design and device engineering. In this work, three small molecular acceptors with different terminal steric hindrance groups (Y-PH-H, Y-PH-CH3, and Y-PH-2CH3) are designed as the third components to elaborately reduce the π-π interactions in the acceptor phase and improve the photoluminescence quantum yield (PLQY). All the third components effectively improve the fluorescence quantum yield of the acceptor phase and inhibit ΔEnr. Among these systems, the Y-PH-CH3 ternary system exhibits remarkable suppression of non-radiative energy loss, coupled with refined charge transport capabilities. Consequently, it achieves an impressive power conversion efficiency (PCE) of 18.63%, accompanied by a low non-radiative energy loss of merely 0.178 eV. Moreover, by adopting this third component design strategy into D18:L8-BO system, significantly improved open circuit voltage (VOC) of 0.924 V, and high PCE of 19.18% can be achieved. This study confirms that appropriately manipulating the planarity of acceptor by terminal steric hindrance groups is an effective approach for designing third component toward highly efficient ternary OSCs with low ΔEnr.