The effects of in situ phosphorus doped LPCVD polysilicon thickness on the electrical and photovoltaic characteristics of poly-emitter solar cells subjected to higher processing temperatures are studied. The factors which control the fill factor of the solar cells are analytically examined and it is shown that the fill factor is a strong function of the open-circuit voltage and ideality factor, in addition to the other well known parameters such as series and shunt resistances. From the experimental studies it is shown that better performance of poly-emitter solar cells can be achieved when the in situ doped LPCVD polysilicon layer thickness is about 0.2 mu m.