Advancing organic photovoltaics processed from green-solvents: From characterization methods to optimization strategies

The organic solar cell (OSC) technology has advanced significantly during the past decade, with power conversion efficiencies now exceeding 20%. However, the fabrication of high-performance devices still relies on using halogenated solvents, which pose environmental risks and limit industrial scalability. To address this issue, researchers are developing new strategies such as new molecular design concepts, control of blend morphology through processing conditions, and performance optimization guided by charge carrier mechanisms aiming to enhance solubility in green solvents while ensuring optimal film formation, as to be summarized in this review. Despite these efforts, the complex chemical/morphological structure-processing-property-function relationships remain elusive. A deeper understanding of film formation dynamics and consequences in charge carrier dynamics is essential, thereby necessitating both ex-situ and in-situ morphological and optical characterizations. Accordingly, this review begins with an overview of the key reminders for commonly used characterization techniques together with solvent properties, and solubility-morphology relationships. Ultimately, this review highlights the latest advancements in materials and device engineering and discusses the challenges that the field must overcome to enable more sustainable and scalable OSC fabrication.