Material cost issues in OPVs

The performance of both types of composites in OPVs is still modest as compared to semiconductor-based solar cells. Improvement in the layer morphology and development of low-bandgap organic materials can lead to higher power conversion efficiencies. An estimation of the maximum expectable efficiency of bulk hetero-junction cells predicts that 10% for solar cells will be reached in the next few years, while practical values of 20-25% would be the limits of the best devices, still to be realized [92]. However, even with low but acceptable rj 5%, mass production of low-cost cells will be a nice solution for renewable energy sources. The main and difficult to solve issue is the stability of the devices, which should attain industrial commercialization requirements. Stable operation for more than 4000 h has been reported for P3HT PCBM bilayer structure cells and can be further improved [93]. 

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