Efficiency enhancement of polymer solar cells by patterning nanoscale indium tin oxide layer

The efficiency of polymer solar cells was improved by patterning indium tin oxide (ITO) electrode layer in this work. Light absorbance was enhanced with ITO layer patterning resulting in the improvement of power conversion efficiency of polymer solar cells. The line-and-space grooved patterns of polystyrene layer are formed on the top of 100 nm thick indium tin oxide layer by capillary force lithography process. The surface patterning of the ITO layer were completed with O2 and Ar plasma etching with various step heights of 22 nm to 64 nm. The active layer was fabricated with one-to-one ratio of P3HT (poly-3-hexylthiophene) and PCBM ([6,6]-phenyl C61-butyric acid methyl ester) conjugated polymers on the top of the patterned ITO layer. Efficiency of the polymer solar cell was improved from 0.96% to 1.35% with this approach. We attribute the efficiency improvement to periodic grooved patterns of electrode. The periodic grooved patterns are believed to enhance light trapping resulting in the increase of diffraction and also to increase contact area of the electron-collecting electrode leading to increase of short circuit current.