Ultra-Stable ITO-Free Organic Solar Cells and Modules Processed from Non-Halogenated Solvents under Indoor Illumination.

Organic Photovoltaics (OPV) is a very promising technology to harvest artificial illumination and power smart devices of the Internet of Things (IoT). Efficiencies as high as 30.2% have been reported for OPVs under warm white light-emitting diode (LED) light. This is due to the narrow spectrum of indoor light, which leads to an optimal bandgap of ≈1.9 eV. Under full sunlight, OPV devices often suffer from poor stability compared to the established inorganic PV technologies such as crystalline silicon. This study focuses on a potentially very cost-effective Indium Tin Oxide (ITO) free cell stack with absorber materials processed from non-halogenated solvents. These organic solar cells and modules with efficiencies up to 21% can already achieve remarkable stabilities under typical indoor illumination. Aging under 50,000 lux LED lighting leads to very little degradation after more than 11 000 h. This light dose corresponds to more than 110 years under 500 lux. For modules encapsulated with a flexible barrier, extrapolated lifetimes of more than 41 years are achieved. This shows that OPV is mature for the specific application under indoor illumination. Due to the large number of potential organic semiconducting materials, further efficiency increase can be expected.