The light-to-electricity conversion efficiency is of critical interest for the laser power beaming technology. The coupled interaction between electricity conversion and heat generation determines the actual light-to-electricity conversion efficiency. In this paper, a coupled model is established to describe such coupled interaction and the equilibrium point of laser illuminated Photovoltaic (PV) cells. A simplified equation is developed to solve the equilibrium temperature and the electricity conversion efficiency of a thin-film PV cell evenly illuminated by a laser. Numerical examples are provided for typical conversion conditions and a preliminary parametric study with sensitivity analysis is carried out for future system design.