Enabling Roll-Processed and Flexible Organic Solar Cells Based on PffBT4T Through Temperature-Controlled Slot-Die Coating

Although the mark of 18% power conversion efficiency (PCE) was surpassed recently, organic solar cells (OSCs) still have several challenges to overcome in order to fully compete with silicon-based solar cells in the energy market. One of the main challenges is the upscaling of the technology. Despite the recent advances in PCEs, a big scalability gap still exists between the best lab-scale device and large-scale modules fabricated via roll-to-roll processing. The polymer donor PffBT4T-C9C13 has already shown efficiencies of almost 12% together with PCBM. Combined with the nonfullerene acceptor O-IDTBR, a reduced voltage loss of 0.5 V between the optical band gap and VOC is obtained, with an open-circuit voltage up to 1.12 V, which is one of the highest values reported for OSCs. In this work, we demonstrate a route to upscaling OSCs based on PffBT4T-C9C13:O-IDTBR through temperature-controlled slot-die coating, solving the challenges of the temperature dependent aggregation behavior, which strongly affects the efficiency of the device. Efficiencies above 4% were achieved in our flexible and roll-processed devices with an area of ∼1 cm2 and the different origins of the scalability lag were studied. As an additional necessary step for scalability, we incorporate the use of a hydrocarbon-based solvent to remove the environmentally dangerous halogenated solvents. To the best of our knowledge, this is the first work reporting PffBT4T:O-IDTBR solar cells fabricated in open air using slot-die coating in a roll-platform with flexible substrates, that mimics large-scale roll-to-roll processing.