Life cycle assessment of ITO-free flexible polymer solar cells prepared by roll-to-roll coating and printing

Indium is a scarce and expensive material that has been identified as a bottleneck for future organic electronics deployment in large scale. Indium is the main constituent of Indium Tin Oxide (ITO), which is the most successful transparent electrode in organic photovoltaics (OPV) so far. A new process, termed Hiflex, allows for manufacture of flexible OPV modules where the ITO electrode has been replaced by a sputtered Al/Cr electrode in an inverted device architecture with front illumination. This work presents a life cycle assessment of the Hiflex process, in order to compare the environmental impact of avoiding ITO as electrode. The new ITO-free process reduces some of the processing steps, leading to important reductions of the energy input during OPV module manufacturing in comparison to ITO-based modules. The environmental analysis reveals an Energy Pay-Back time (EPBT) of 10 years due to the high-energy consumption of Al/Cr roll-to-roll sputtering and to the relatively low efficiency of the Hiflex OPV modules (≈1%). An optimization of the active area fraction could easily reduce the EPBT to ≈5 years. A further enhancement of the efficiency to 5% would give rise to a promising EPBT of only 1 year. Our work highlights that vacuum processing steps should be avoided.