Abstract
Polycrystalline CuIn1-xGaxSe2 (CIGS) solar cell with the highest efficiency was reported using three-stage co-evaporation, which suffers from large-scaled mass manufacture. The alternative approach is to use two-step process. However, the annealing process is usually under H2Se which is toxic to get the high efficiency. Therefore, simplifying the process for fabricating CIGS thin films is very essential. Polycrystalline CuIn1-xGaxSe2 thin films sputtered from a quaternary target is a promising method. However, the small grain sizes are got by using Cu-poor target. According to Jesse A. Frantz’s research[1], the presence of grain boundaries would affect the diffusion length and transport of carriers through this layer reducing the short circuit current. Moreover, as-deposited films are with current-blocking effect which is very harmful to the fill factor and open circuit voltage. Therefore, we study selenization on the polycrystalline CuIn1-xGaxSe2 thin films sputtered from a quaternary target and try to improve the efficiency. There are two parts in the study. First, we deposited films under low temperatures and selenization under high temperatures. At high temperatures, MoSe2 is thick and the composition deviation of films was serious. The efficiency is not so good finally. In order to solve these problems, we deposited films under high temperatures and selenization under low temperatures to inhibit current-blocking effect. We increase the activity of selenium vapor by changing the graphite box design and improve the fill factor and open circuit voltage successfully. Finally, the device yielded the efficiency of 8.6%.