Long-term stability of dye-sensitised solar cells

Accelerated ageing tests on large numbers of nanocrystalline dye-sensitised solar cells (ne-DSC) show that, to first order, separation between the effects of the stresses of visible light soaking, UV illumination and thermal treatment on long-term stability is possible. The corresponding mechanisms are electrochemical, photochemical and purely chemical in nature. It was found that visible light soaking alone is not a dominant stress factor. A dramatic improvement in UV stability has been achieved by using MgI2 as additive to the electrolyte. Thermal stress appears to be one of the most critical factors determining the long-term stability of nc-DSC and is strongly related to the chemical composition of electrolyte solvents and additives. Encouraging stability results have been obtained for cells based on pure nitrile-based solvents: (1) A minor decrease in performance of initially 5.5% solar efficient cells has been found after 2000 h at 60 degreesC without light soaking; (2) After 900 h ageing at 85 degreesC, a decrease of 30% in maximum power has been observed; (3) After 3400 It of combined thermal stress and continuous light soaking (45 degreesC, 1 sun equivalent) good stability with 15% decrease in maximum power can be demonstrated. It should be noted that such good thermal stability has not been reported previously for dye-sensitised solar cells so far. Copyright (C) 2001 John Wiley & Sons, Ltd.