Effect of reduced deposition temperature, time, and thickness on Cu(InGa)Se2 films and devices

This paper addresses the ability to reduce process costs for the multisource evaporation of Cu(InGa)Se₂ by reducing the deposition temperature and film thickness and increasing the deposition rate. Substrate temperature (T_ss) is varied from 600⩾T _ss⩾350°C using fixed elemental fluxes. The grain size decreases over the entire range but Na incorporation from the soda lime glass substrate does not change. Solar cell efficiency decreases slowly for 550⩾T_ss⩾400°C. At T_ss below 400°C there is a change in composition attributed to a change in the re-evaporation of In and Ga species in the growing film. Device performance is shown to be unaffected by reducing the film thickness from 2.5 to less than 1.5 μm. Finally, a kinetic reaction model is presented for the growth of CuInSe₂ by multisource elemental evaporation which provides quantitative predictions of the time to grow CuInSe₂ films as a function of substrate temperature and delivery rate