Ageing of DSSC studied by electroluminescence and transmission imaging

Outdoor stability testing of ionic liquid based dye sensitised solar cells under short circuit (SC) and open circuit (OC) modes has been followed using electroluminescence (EL) and transmission imaging. The study showed a significant influence of the ageing conditions on the stability of the solar cell parameters in the exposure period from zero up to 31 kWh/m2 (four summer days) of solar irradiation. Initial exposure is beneficial for all performance parameters regardless the operating mode under which the cells were aged. After 8 kWh/m2 ageing of the cells in SC mode downgrades all parameters, mainly Jsc and consequently η, while continues ageing in OC mode slightly increases Voc and consequently η. The EL imaging demonstrated that ageing, regardless the operating mode, is associated with the growth of the EL inactive areas that appear as black spots or defects, which we associate with the formation of iodine species in the electrolyte that have been captured under confocal microscope. The stability testing demonstrates that growth of the defects is more pronounced for cells operated in SC mode, which primarily reduces stability of Jsc.