Structural optimization and performance analysis of quantum-dots-sensitized solar cells

Abstract

At present, the photoelectric conversion efficiency of the liquid junction quantum dot-sensitized solar cells(QDSSC) has reached 6.5%,but this value is still far from the theoretical maximum efficiency of 44%. Therefore, further optimization of the cell structure and fabrication technology are required to enhance solar cell performance. In this paper, a compact TiO2 thin film, prepared by a sol-gel method, is introduced between the FTO conducting substrate and the mesoporous TiO2 electrode. This compact TiO2 film is used as a barrier layer to prevent the direct contact between FTO substrate and electrolyte, and therefore suppress the back electron transfer from FTO to electrolyte. The structure, surface morphology, and optical properties of this compact TiO2 film are characterized by XRD,SEM, AFM, and UV-vis spectrum. The results show that this TiO2 film with smooth surface is mainly an anatase structure, and it has good light transmission in visible light region. Compared with the QDSSC without this compact TiO2 layer, the short-circuit current density, open-circuit voltage, and solar energy conversion efficiency of the QDSSC with the compact layer are improved by 47.2%,4.2% and 34.8%, respectively. Meanwhile, the influence of the thickness of TiO2 barrier layer on photoelectric properties of QDSSC is investigated, and we find that the efficiency of the cell is decreased while increasing the thickness of barrier layer. That can be attributed to that the increase of the thickness can reduce the transmittance of photoanode, and the resistance of TiO2 barrier layer will also increase, which may adversely influence the electron transportation between the mesoporous TiO2 electrode and FTO substrate.