New Ternary Blend Strategy Based on a Vertically Self-Assembled Passivation Layer Enabling Efficient and Photostable Inverted Organic Solar Cells

Efficient Ternary Organic Solar Cells with Suppressed Nonradiative Recombination and Fine-Tuned Morphology via IT-4F as Guest Acceptor

The large open circuit voltage (VOC) loss is currently one of the main obstacles to achieving efficient organic solar cells (OSCs). In this study, the ternary OSCs comprising PM6:BTP-eC9:IT-4F demonstrate a superior efficiency of 18.2 %. Notably, the utilization of the medium bandgap acceptor IT-4F as the third component results in an exceptionally low nonradiative recombination energy loss of 0.28 V. The desirable energy level cascade is formed among PM6, BTP-eC9, and IT-4F due to the low-lying HOMO and LUMO energy levels of IT-4F. More importantly, the VOC of PM6:BTP-eC9:IT-4F OSCs can reach as high as 0.86 V, which is higher than both binary OSCs without sacrificing JSC and FF. Besides, this strategy proved that IT-4F can not only broaden the absorption range but also work as a morphology modifier in PM6:BTP-eC9:IT-4F OSCs, and there also exists efficient energy transfer between BTP-eC9 and IT-4F. This result provides a promising way to suppress the nonradiative recombination energy loss and realize higher VOC than the two binary OSCs in ternary OSCs to obtain high power conversion efficiencies.

Overcoming the Interfacial Photocatalytic Degradation of Nonfullerene Acceptor-Based Organic Photovoltaics by Introducing a UV-A-Insensitive Titanium Suboxide Layer

Although recent dramatic advances in power conversion efficiencies (PCEs) have resulted in values over 19%, the poor photostability of organic photovoltaics (OPVs) has been a serious bottleneck to their commercialization. The photocatalytic effect, which is caused by incident ultraviolet-A (UV-A, 320-400 nm) light in the most commonly used zinc oxide (ZnOX) electron transport layer (ETL), significantly deteriorates the photostability of OPVs. In this work, we develop a new and facile method to enhance the photostability of nonfullerene acceptor-based OPVs by introducing UV-A-insensitive titanium suboxide (TiOX) ETL. Through an in-depth analysis of mass information at the interface between the ETL and photoactive layer, we confirm that the UV-A-insensitive TiOX suppresses the photocatalytic effect. The resulting device employing the TiOX ETL shows excellent photostability, obtaining 80% of the initial PCE for up to 200 h under 1 sun illumination, which is 10 times longer than that of the conventional ZnOX system (19 h).