Solution processed polymer tandem cell utilizing organic layer coated nano-crystalline TiO2 as interlayer

A solution processed polymer tandem cell has been fabricated by utilizing organic layer coated TiO2 nanoparticle (OL-TiO2) as an interlayer. The crystalline phase of the OL-TiO2 was anatase. The dispersed solution of the OL-TiO2 showed high optical transparency and excellent film forming property. The top and bottom cell were clearly separated by the OL-TiO2 interlayer without interlayer mixing, which was not observed for the tandem cell utilizing commercially available TiO2 nanoparticle (N-TiO2) as an interlayer. The conversion efficiency of a polymer tandem cell was enhanced from 1.43% to 3.44% by replacing the interlayer from N-TiO2 to OL-TiO2. The tandem cell performance was further enhanced by adjusting the thicknesses of the active layers in the subcells and adjusting the conductivity of the PEDOT:PSS layer in the bottom cell. The highest conversion efficiency of 3.66% was obtained from the tandem cell having the structure of ITO/Baytron P VP AI 4083/P3HT:PCBM (100 nm)/OL-TiO2/Baytron PH 500/P3HT: PCBM (100 nm)/Al. In addition that, it was found that the OL-TiO2 interlayer enhanced the stability of the tandem cell comparing to that of the single junction cell by the reduction of the oxygen diffusion to the bottom layer by the interlayer. It is expected that the performance of the tandem cell can be further enhanced by adopting efficient low band gap materials. (C) 2009 Elsevier B. V. All rights reserved.