Upscaling from single cells to modules – fabrication of vacuum- and ITO-free polymer solar cells on flexible substrates with long lifetime

Abstract

Fabrication of polymer solar cell (PSC) modules was done on a previously reported compact coating/printing machine and tested in a readily scalable roll process on flexible substrates without applying vacuum, ITO or spin coating. Our aim was to establish loss upon scaling from cells to small modules. We studied from single cells (1 cm²) to modules comprising four serially connected devices with a total active area of 8 cm². Four different polymers (P3HT, PV-D4610, PDTSTTz-4 and PBDTTTz-4) were applied in the preparation of the modules and efficiencies of more than 3% were achieved which is comparable to single cell devices prepared using the same process. This proves that it is possible to scale up new materials in an ITO free device context to modules without having an efficiency drop, due to reliable and consistent processing. The main loss observed was due to the packaging using barrier materials. The photochemical stability of the materials was therefore studied using intense light along with the operational stability of the corresponding devices according to the ISOS-D-1 and ISOS-L-1 standards. For devices under constant illumination we found that barrier materials from Mitsubishi and 3M provide better operational stability over time, compared to the barrier foil obtained from Amcor, for all the polymers, which is ascribed to the cut-off at higher wavelengths thereby lowering the degree of UV light that reaches the device. When comparing the operational stability of the four polymers under constant illumination, P3HT generally retains its performance better with higher T₈₀ values, while the polymer PV-D4610 shows the highest PCE (1.6%) after 300 hours of operation.