Understanding the Effect of Sequential Deposition Processing for High-Efficient Organic Photovoltaics to Harvest Sunlight and Artificial Light

As the market of the Internet of Things (IoT) increases, great attention has been paid to the development of high-efficient organic photovoltaics (OPVs) utilizing artificial light. However, in a real indoor condition, the power density contribution of the artificial light cannot exceed 35% in the combination of indoor and outdoor irradiation, which indicates that the illumination of sunlight cannot be ignored during daytime. Hence, it is urgent to develop high-efficient OPVs in indoor conditions taking into account both sunlight and artificial light. In this work, a novel asymmetric molecule TB-4F was synthesized to trade-off the absorption spectrum that can be applied under both artificial light and sunlight. In conventional bulk-heterojunction (C-BHJ), it was figured out that due to nonoptimal morphology some carriers failed to be efficiently collected. Herein, a sequential deposition bulk-heterojunction (SD-BHJ) as an alternative fabrication method successfully enhanced the performance of OPVs, under both artificial light and sunlight, which was attributed to the favorable microstructure being vertically distributed in the active layer. Notably, the PCE was significantly increased by 25% for SD-BHJ compared to C-BHJ under artificial light, owing to the strong effect of trap-assisted recombination and dark current on PCE in the condition of low carrier density. Our result indicates that an asymmetric molecule with a blue-shifted spectrum fabricated by SD-BHJ can be a promising candidate that can be applied in indoor environments to harvest sunlight and artificial light simultaneously.