Organic solar cells P3HT:PCBM devices

A number of approaches are being pursued to modify the electrodes in organic solar cells in order to improve conductivity, selectivity, stability or cost. These include new electrode materials, changes in device processing and additional electrode sub-layers. Most studies have been carried out using the leading material combination, P3HT PCBM, as the active layer. 

A hybrid HBETL material composed of polymerized fiiUerene derivative (C-PCBSD, Figure 78) and ZnO was introduced by Hsieh et al Inverted P3HT/[60]PCBM organic solar cells with ITO cathode covered with ZnO buffer layer yielded power conversion efficiency of 3.5%. On the contrary, devices comprising hybrid HBETL represented by ZnO/poly-C-PCBSD junction yielded much higher power conversion efficiency of 4.4% mainly due to the increased photocurrent density (/sc = 12.8 mA cm )... 

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]. 

Glatthaar et al. deposited a commercially available PEDOT PSS formulation (Clevios CPP 105D ) on top of the photoactive layer to form inverted solar cells. In contrast TCO layers when used as top electrode will damage the sensitive organic active layer, for example, P3HT PCBM, owing to the sputter-deposition process, and as a consequence the devices will not function. The concept of polymeric top electrodes allows also the fabrication of semitransparent solar cells. ° ... 

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