Photoinduced spin-orbital coupling effect at donor: acceptor interface in non-fullerene organic solar cells

Abstract

Non-fullerene based organic solar cells show excellent optoelectronic properties. In this study, firstly, we measured the magneto-photocurrent (MPC) effect to monitor the spin orbit coupling (SOC) action of electron-hole pairs at the donor: acceptor (D:A) interfaces, introduced by the dipole-dipole interaction in non-fullerene ITIC molecules. The MPC of non-fullerene based bulk heterojunctions show a broader line-shape, which implies a stronger SOC in electron-hole pairs at D:A interface as compared to the fullerene based bulk heterojunctions under photo-excitation. Secondly, the light-induced electron paramagnetic resonance (LEPR) results further give a direct evidence for stronger SOC in electron-hole pairs at D:A interface in non-fullerene bulk-heterojunction. Theoretically, increasing SOC provides a pathway for singlet electron-hole pairs to convert into triplet electron-hole pairs, leading to more spin states ready for dissociation. Therefore, the increased SOC will increase the magneto-photocurrent, and improve the performance of non-fullerene solar cells, we consider that photoexcitation can present a new approach to strengthen the SOC effect in organic solar cells toward better photovoltaic actions. Non-fullerene based organic solar cells show excellent optoelectronic properties and device performance. We think these excellent properties come from a stronger spin orbit coupling effect in electron-hole pairs at D: A interface under photoexcitation as compared to the fullerene bulk-heterojunctions, leading to increase the magneto-photocurrent. In addition, the capacitance-frequency is also reveal that the stronger SOC for non-fullerene bulk-heterojunctions originates from the larger electron cloud deformation electron-hole pairs caused by photoinduced dipole-dipole interactions. Therefore, we think the photoexcitation present a new approach to strengthen the SOC effect in organic solar cells toward better photovoltaic actions. • Non-fullerene based solar cell of ITO/ZnO/Active layer/MoO 3 /Ag shows a higher PCE of 11.30%. • A strong SOC exists in electron-hole pairs at D:A interface in the non-fullerene under lighting. • The strong SOC comes from the larger electron cloud deformation. • Photo-excitation can present a new approach to strengthen the SOC effect in organic solar cells.