Effects of Temperature and Intensity on Thermodynamic Limits for Efficiencies of Photochemical Conversion of Solar Energy

Abstract

The subject of thermodynamic limits on photochemical conversion of light to work has been of considerable interest for over twenty years. Recently, Ross and Hsiao calculated quantum conversion efficiencies for solar radiation at air mass zero (AMO). Bolton later extended this treatment to AM1.2 solar flux and also considered some kinetic as well as thermodynamic limitations. These methods are applied to a variety of solar intensities and absorber temperatures. Also, improvements in efficiency which can be obtained by using systems with several absorbers of different effective band-gap wavelengths are examined. The results, which are applicable to photovoltaic as well as to photochemical and photobiological conversion devices, represent absolute (i.e., ideal) upper limits on conversion efficiencies, analogous to Carnot efficiencies of heat engines. Also, calculations for two-photon processes (i.e., two discrete absorbers) are carried out over a limited range of temperature-intensity combinations. The treatment is extended to calculate the optimum wavelengths for multiphoton cases (3 less than or equal to n less than or equal to 8) at fixed temperature and intensity. (WHK)