Suppressing nonradiative energy loss in ternary organic solar cells through elaborate disruption of guest acceptors planarity†

Abstract

The relatively large non-radiative energy loss (ΔE_nr) in organic solar cells (OSCs) remains a major obstacle for improving the power conversion efficiency (PCE). Therefore, it is imperative to minimize ΔE_nr through rational molecular design and device engineering. In this work, three small-molecule acceptors with different terminal steric hindrance groups, namely, Y-PH-H, Y-PH-CH₃, and Y-PH-2CH₃, were 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 improved the fluorescence quantum yield of the acceptor phase and inhibited ΔE_nr. Among these systems, the Y-PH-CH₃ ternary system exhibited remarkable suppression of non-radiative energy loss, coupled with refined charge transport capabilities. Consequently, it achieved 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 a D18:L8-BO system, a significantly improved open circuit voltage (V_OC) of 0.924 V and a high PCE of 19.18% could be achieved. This study confirms that appropriately manipulating the planarity of acceptors by terminal steric hindrance groups is an effective approach for designing third components toward highly efficient ternary OSCs with low ΔE_nr.