A photon-enhanced thermionic solar cell (PETSC) is a new type of solar energy conversion device that simultaneously uses light and heat from the sun. In this paper, a PETSC model is briefly described, which includes the thermal radiation between the cathode and the anode and the heat losses from the two electrode plates to the environment. Analytic expressions are derived for the power output and overall efficiency of the PETSC. Energy balance equations are used to calculate the operating temperatures of the cathode and anode electrodes for given values of the band gap energy and electron affinity of the cathode material. The performance characteristics of the PETSC are determined by numerical calculation. The maximum efficiency of the PETSC is clearly larger than that of traditional thermionic devices or solar cells. The optimal values of the band gap energy and electron affinity of the cathode material at the maximum efficiency are determined, and consequently, the operating temperatures of the cathode and anode electrodes can be optimally designed. The results obtained in this study may provide guidance for the appropriate selection of cathode materials and the optimum design of practical PETSC devices. (C) 2013 Published by Elsevier B.V.