The presence of self-assembled nano-ridged (SANR) structures in PTB7-Th:PC₇₀BM:PC₆₀BM ternary organic blend film with the specific component ratio was experimentally clarified, and the light-trapping effect of the SANR structures was demonstrated. On this basis, the light-trapping characteristics of the PTB7-Th:PC₇₀BM:PC₆₀BM ternary blend film with the SANR structures were investigated by using the finite-difference time-domain (FDTD) algorithm. The results showed that the SANR structures have a light-trapping effect, which can effectively reduce the transmittance and reflectance of the incident photons at the specific wavelengths and thus exhibit stronger photon absorption, especially for the photons in the wavelength range of 550–650 nm. The light-trapping effect of the SANR structures does not depend on the direction of photon incidence, and the active layer traps the photons incident from both its top and bottom. The dimensional variation of the SANR has a significant effect on the light-trapping characteristics of the active layer, and the effect caused by the height variation is overwhelmingly superior compared with that of the width variation. In addition, the higher the density of the SANR, the more significant the light-trapping effect of the active layer. This work provides a theoretical basis for the further experimental enhancement of the photon absorption capacity of the PTB7-Th:PC₇₀BM:PC₆₀BM active layer with SANR structures.

The cathode buffer layer (CBL) plays a crucial role in organic solar cells (OSCs), and it has been challenging to obtain high-quality CBL by using simple and reliable processes. In this paper, the bilayer structure consisting of ZnO nanoparticles (NPs) and sol–gel SnO₂ was prepared by the low-temperature (<100 °C) UV-ozone (UVO) sintering process and used as the robust CBL for ternary OSCs based on PTB7-Th:PCDTBT:PC₇₀BM. The results show that the insertion of SnO₂ can effectively fill the cracks and pores on the surface of the ZnO NP film, thereby improving the overall compactness and flatness of the CBL and reducing the defect density inside the CBL. Furthermore, the insertion of SnO₂ slightly improves the transmittance of the CBL to photons with wavelengths in the range of 400–600 nm, and also increases the electron mobility of the CBL thus facilitating the extraction and transport of the electrons. Compared to the devices using UVO-ZnO and UVO-SnO₂ CBLs, the devices with UVO-ZnO/SnO₂ CBL exhibit exceptional performance advantages, the best power conversion efficiency (PCE) reaches 10.56%. More importantly, the stability of the devices with ZnO/SnO₂ CBL is significantly improved, the device (PCE) still maintains 60% of the initial value after 30 days in air. The positive results show that the UVO-ZnO/SnO₂ is an ideal CBL for OSCs, and due to the low-temperature process, it has great application potential in flexible OSCs.