ITO‐Free Indoor OPV Modules from Nonhalogenated Solvents

The growing market of the internet‐of‐things (IoT) accelerates the development of indoor organic photovoltaics. Very high performances up to 29% are already achieved under illumination with white light‐emitting diodes with intensities in the range of 500–1000 lux. However, topics relevant for mass production such as large area coating, use of nontoxic solvents, and inexpensive electrodes are hardly addressed thus far. Herein this work, an indium‐tin‐oxide‐free device stack is presented, which shows very good performance with many novel absorber materials under both full sun light as well as indoor illumination. Furthermore, lab‐scale cells are upscaled to small modules that can power typical IoT devices. This includes the transition from spin coating to slot‐die coating as well as the use of green solvents. Further, as the parallel resistance (RP) is crucial for the performance under low illumination intensities, a detailed analysis is carried out and it is found that a one‐diode model with the RP being determined from the dark current–voltage characteristics reproduces the behavior quite accurately. Efficiencies of 19.3% on cell level and above 17% on an 8.1 cm2 module with eight interconnected cells are achieved under 500 lux cold white light‐emitting diode illumination. Energy harvesting by indoor photovoltaics is a very promising candidate to supply the energy for the demand of billions of internet‐of‐things devices. The indium‐tin‐oxide‐free organic photovoltaic modules presented herein show great potential to fulfill these needs. Their large parallel resistance enables use cases at ultralow intensities of 50 lux, which is exceptional in this field.