Self-organized cholesteric liquid crystal polymer films with tunable photonic band gap as transparent and flexible back-reflectors for dye-sensitized solar cells

Abstract

Dye-sensitized solar cells (DSCs) have attracted widespread attention in recent years, attributed to their low production costs, facile fabrication and tunable optical properties. In order to achieve competitive conversion efficiencies, the sunlight harvesting capacities of DSCs should be improved over a broad range of wavelengths and incidence angle. Here, we demonstrate a facile strategy to enhance the light absorptions of the devices via employing self-organized cholesteric liquid crystal (CLC) polymer films as transparent and flexible back-reflectors for DSCs. The photonic band gap of these CLC films can be precisely tailored by modulating the helical pitch and twist sense. The selective light reflection of these CLC films gives rise to the possibility for increasing the optical path length of the light in particular wavelength region while retaining the cell transparency. The enhancement of photocurrent and power conversion efficiency (PCE) reveals strong wavelength dependence owing to the selective reflection of these CLC polymer films. The DSCs with proper combination of CLC back-reflectors yield the maximum enhancement over 21% in photocurrent and 17% in PCE. The work presented here provides new insights into the design of cell geometry for achieving extra absorption enhancement, which can also be compatible with other photovoltaic concepts.