Cu(In,Ga)Se2 thin-film solar cells grown with cracked selenium

Cu(In1−xGax)Se2 (CIGS) films have been grown by using cracked selenium. In conventional evaporation system, the Se atoms were supplied as large clusters (Sex, x>5). However, the size of clusters can be reduced by the thermal cracking. The film qualities grown with small clusters (Sex, x<4) would be improved, since the smaller size molecules easily react with elemental metals, resulting in the reduction of selenium vacancies and the enhancement of surface migration. The CIGS films were deposited by the three-stage method with cracked selenium, and the films were evaluated by SEM, XRD, EDX, C–V measurement and admittance spectroscopy. It was found from the C–V characteristics that the carrier concentrations of the CIGS films grown with cracked selenium were increased with increasing the cracking temperature. The result clearly showed that the use of cracked selenium was effective for reduction of selenium vacancies. The conversion efficiency of 15.4% was obtained by using cracked selenium at a cracking temperature of 500 °C.