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 (R-P) 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 R-P 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 cm(2) module with eight interconnected cells are achieved under 500 lux cold white light-emitting diode illumination.