Nonhalogenated Photoactive Layer PBDB‐T:BTP‐M‐Based Organic Solar Cells with Efficient and Stable Performance

While state‐of‐the‐art organic photovoltaics (OPVs) have been achieved by halogen modification strategies for active layer materials, the stability of these OPVs can be compromised by the presence of halogen ions at the interface and within the photoactive layer. Herein, halogen‐free photoactive layer‐based OPV cells are fabricated and systematically studied to understand and explore the working principle and potential of this class of OPV devices. For the first time, a champion efficiency of 13.12% is achieved for the inverted device (ITO/AZO/AL/MoO 3 /Ag) based on the nonhalogenated photoactive layer PBDB‐T:BTP‐M. Superior metal electrode stability is confirmed for the unencapsulated PBDB‐T:BTP‐M devices aged at 85 °C in the air atmosphere compared to the halogenated PM6:Y6 devices. Specifically, better thermal stability is verified for the nonhalogenated device without 1‐chloronaphthalene (1‐CN) additive compared to the device with 1‐CN additive, with 89% of the initial efficiency retained after being aged for 900 h at 85 °C in the N 2 atmosphere. These results evidence the halogen/halide impacts on device stability and demonstrate the potential for nonhalogenated OPVs to achieve efficient and stable performance, benefiting the development and practical application of this technology.