Progress of additives for morphology control in organic photovoltaics

The microstructure of the active layer in organic photovoltaics (OPVs), such as the size of phase separation, purity of the phases, and molecular packing within each phase, plays a crucial role in influencing the behavior of excitons and charge carriers within the active layer. It is also a key determinant of the photovoltaic performance of the device. During the optimization of OPV devices, the use of additives has been demonstrated to be an effective strategy in microstructure control, leading to enhanced performance. Therefore, the quest for stable and efficient novel additives, along with an exploration and summarization of the mechanisms underlying additive-induced microstructure control, is essential for a better understanding of the developmental trends of high-performance additives. In this review, we categorize additives based on their chemical structures and discuss their effects on the microstructure of the active layer from both thermodynamic and kinetic perspectives. Furthermore, we elaborate on the working mechanisms and their impact on the photovoltaic performance of the devices. This review provides an overview of recent advances in additives for OPVs, offering potential guidance for the future development of additives and further optimization of the active layer in photovoltaic devices.