Improved Thermal Stability of Polymer Solar Cells by Incorporating Porphyrins

Thermal stability has been the important issue in organic solar cell, especially for the large scale fabrication and application in the future. In this work, a new strategy involving the introduction of porphyrin compound (BL) is proposed to prevent the [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) aggregation. The supramolecular interactions between PC61BM and BL are first demonstrated in PC61BM:BL binary blend, and then the effect of BL on P3HT:PC61BM blend is qualitatively and quantitatively studied by differential scanning calorimetry, UV-vis absorption spectroscopy, atomic force microscopy, optical microscopy, and fluorescence techniques. It is found that the BL addition not only stabilizes the morphology of P3HT:PC61BM blend films, but also shows a good ability to maintain the electron mobility by depressing the PC61BM crystallization. And the thermal stability of the devices based on P3HT:PC61BM:BL ternary blend films is therefore greatly improved. For example, 8 wt% BL doping drops the power conversion efficiency by 10.5% relative to its peak value after 48 h of annealing at 130 degrees C, while 71.5% of decrease is obtained for the device without BL after only 3 h of annealing. This strategy is preliminarily proved to be universal and will show great potentials in future commercialization of polymer solar cells.