The effect of light environment during the film formation process on the morphology and function of organic photovoltaics

In the reported fabrication process of organic photovoltaics (OPVs), the effects of the light environment are usually thought to be negligible, and so are not included in the experimental section of a paper. In this work, the morphology of organic bulk-heterojunction (BHJ) photovoltaics in the presence and absence of white light during the film formation process was examined by using small-angle neutron scattering and grazing incidence X-ray scattering. We provide the first clear experimental evidence that the morphology, thermodynamics and function of BHJ blends are significantly impacted by photo absorption during the film formation process. The results clearly demonstrate that the crystal sizes of donor materials decrease, while the size of the pure acceptor phase increased with an increase in the light intensity along with enhanced acceptor aggregates. Moreover, the specific interfacial area between the pure acceptor phase and its surrounding matrix is found to be crucial for the electron transport and device performance, which reaches a maximum under 1 sun illumination, resulting in the best device. The generalization of the impact of light illumination was also investigated in other OPV systems, including the fullerene and non-fullerene systems. These findings opened the door to a wide range of applications, such as providing simple illumination during the processing of organic semiconductor-based devices to precisely control the morphology, and surely expend the application of illumination for further improvements in the OPV performance.