ABSOLUTE LIMITING EFFICIENCIES FOR PHOTOVOLTAIC ENERGY-CONVERSION

The Detailed Balance Theory was used in the past by a number of author s to calculate the limiting efficiency of photovoltaic energy conversi on. Values of 40.8% for optimum single gap devices and of 86.8% for in finite number of gaps were calculated for the maximum efficiencies of conversion of the radiation of the Sun, considered as a black body at a temperature of 6000 K. This work extends the generality of those res ults and introduces new refinements to the Theory: the cell absorptivi ty is justified to be equal to the emissivity under bias operation and under certain idealistic conditions, the optimization of the absorpti vity is discussed and the concepts of solid angle and energy restricti on are explained. Also, as a consequence of the review, new results ar ise: the maximum efficiency is found to be independent on the concentr ation and although the limiting efficiency of optimum devices is confi rmed, the limiting efficiency previously established for non-optimum d evices is found to have been underestimated under certain circumstance s.