Solution processing of polymer solar cells: towards continuous vacuum-free production

Roll-to-roll (R2R) production is essential for commercial mass production of organic photovoltaics, avoiding energy costs related to the inert atmosphere or vacuum steps. This work provides a complete review of various techniques and materials that have been used for the R2R production of bulk heterojunction polymer solar cells. Various fabrication parameters have been identified and discussed to improve the mass production process, aiming to obtain better-performing devices. The evolution of PCE and FF values of all-solution and partially R2R-processed modules over the last decade has been established, verifying the continuous evolution in this field. The life cycle analyses have confirmed that industrially processed modules through R2R processes have great potential to realize industrial production of high-performance R2R solar cell devices with an immediate goal of 10% PCE, 10 years durability, and less CO₂ emissions with consequent lower energy payback time than other solar technologies. Currently, several laboratories have reported PCE values over 10% for small-area active layers fabricated by R2R techniques. However, the fabrication of large-area modules remains challenging. At the end of this document, based on the collected results, we propose a sequence of R2R compatible processes for an all-solution ITO-free solar device with high performance.