Electronic Organic Thin Film Devices for Solar Energy Harvesting

We have established fabrication process of a multi-layered P3HT/PCBM based bulk-heterojunction photovoltaic cells with the P3HT layer as the hole transport layer and the PCBM layer as the electron transport layer between the electrodes and a blended P3HT/PCBM layer in order to widen the photon harvesting layer. Current density has increased about 1 mA/cm2 by the insertion of P3HT layer and the resulting conversion efficiency has been improved about 20% compared with the single layer device. The device with a cm-scale active area with an efficiency of ~1% has been fabricated by the developed method. We have fabricated the P3HT/PCBM p-i-n BHJ cells for the first time. The device structure was ITO/MoO3/P3HT(p)/P3HT:PCBM(i)/PCBM(n)/Ag. In the as-fabricated cells, the open circuit voltage of p-i-n BHJ cells with PCBM concentration 10 mg/ml, 15 mg/ml and 20 mg/ml were 0.56V, 0.71V and 0.74V respectively, and increased compared with 0.50V in the ordinary BHJ (i-type) cell. After post annealing, the short-circuit current density of p-i-n BHJ cell with PCBM concentration 10 mg/ml has been improved by 20% compared with the ordinary i-type cell and the power conversion efficiency has been also improved by 10% up to over 2%. We have discussed the molecular distribution within the organic layers. We have demonstrated that the organic p-i-n BHJ structure is useful to enhance and optimize power conversion efficiency of the organic thin film BHJ cells.