Improvement in stability of poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl- C61-butyric acid methyl ester bulk heterojunction solar cell by using UV light irradiation

A study of organic solar cells based on photoactive blends of the conjugated regioregular-poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with different UV-light treatments is presented. As expected, air exposure of an unencapsulated P3HT:PCBM solar cell is observed to result in rapid degradation of device efficiency. In order to ease this degradation, we found that exposing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to UV light may reduce the degradation and preserve good performance. Samples with PEDOT:PSS exposed to UV light show better long-run stability than the pristine cells. The active layer exposed to UV light shows the poorest performance and degrades rapidly. From the initial value, the efficiency decreased by 56% and 35% for pristine cells and cells with PEDOT:PSS exposed to UV light, respectively. It has been found that device half-life was 650 and 400 h for the samples with and without UV treatment, respectively. The trend in device performance was explained by observed changes in work function of the PEDOT:PSS layer and decreased absorption intensity of P3HT:PCBM.