TiO2 nanocrystalline layer as a bridge linking TiO2 sub-microspheres layer and substrates for high-efficiency dye-sensitized solar cells

Abstract

TiO2 sub-microspheres possess high surface area and superior light scattering effect which contributes to the high photocurrent density (Jsc) and power conversion efficiency (η) of dye-sensitized solar cells (DSSCs). However, the poor interconnection between the TiO2 sub-microspheres with substrates (N0S4) restricts the electron transport and charge collection. In order to resolve this drawback, we adopted a nanocrystalline monolayer as bridges to contact between the sub-microspheres and substrates (N1S3). The improved contact provides more direct transport channels and increases the increased electron concentration gradient from the top electrode to the bottom electrode, which accelerates the electron transport and charge collection. The combined effects of the faster electron transport rate, less surface states and higher collection efficiency for the N1S3 based DSSC contribute to the higher Jsc and η compared to the N0S4 based DSSC. While the photoelectrodes of N2S2 and N3S1 are too thick of nanocrystalline layer to improve the performance of DSSCs due to the decreased dye loading, reduced light scattering ability and increased crystal boundaries. As a result, a higher η of 10.34% is achieved by introducing the nanocrystalline layer, whereas, only 9.17% is obtained for the photoelectrode without this bridge.