Ambient-Air Ultrasonic Spray Coating at Nanoscale for High-Performance Conducting Polymer/Fullerene-Based Organic Solar Cells

High Resolution Image Download MS PowerPoint Slide Achieving high-performance organic solar cells (OSCs) under ambient-air conditions remains challenging, as the film morphology of the active layer is highly sensitive to environmental variations. Spray deposition proved to be a promising and ambient-environment-compatible solution-processing fabrication method, enabling precise control over the active layer morphology by facile tuning of spray process parameters. In this work, we use ultrasonic spray coating for in-air deposition of the active layer in OSCs, eliminating the need for inert gas environments during solar cell fabrication while maintaining controlled film formation. To provide ambient-air stability and a clear benchmark for nanoscale morphology control, this work revisits the well-established fullerene model system, PTB7-Th:PC 71 BM, and uses it as a representative active layer. Grazing incidence wide-angle X-ray scattering and surface morphology analysis reveal that the flow rate and nozzle movement speed of ultrasonic spray deposition can be effectively exploited to facilitate molecular packing and phase separation that lead to the formation of an ideal nanoscale morphology of the active layer under ambient air, thereby optimizing charge transport. As a result, the in-air spray-coated fullerene OSCs fabricated with the optimized spray-coating parameters achieved a maximum power conversion efficiency of 9.07%, which is comparable to that of spin-coated fullerene devices under similar ambient-air processing conditions. This study establishes an experimentally validated processing guideline and a feasible route for fabricating reasonably efficient OSCs under practical ambient-air conditions, which is expected to be potentially extendable to more advanced non-fullerene and other cutting-edge systems in the future.