Low-temperature processed (Ag,Cu)(In,Ga)Se2 thin film solar cells using Se@Ag2Se core-shell hybrid inks and performance optimization

Abstract

To create (Ag,Cu)(In,Ga)Se2 (ACIGS) thin films using a hybrid ink method, large-scale synthesis of Se@Ag2Se core-shell and Cu-Se nanoparticles was performed, surpassing the scale of previous methods. In particular, although the Se@Ag2Se core-shell was also a precursor for Ag in ACIGS, the amorphous Se (a-Se) in the Se@Ag2Se core-shell acted as a flux during the reaction due to its low melting temperature (221 °C), resulting in the formation of ACIGS thin films at a lower reaction temperature (∼340 °C) and shorter reaction time (30 min) than conventional ones (∼530 °C, 60 min). Furthermore, by varying the amount of Se@Ag2Se core-shell in the hybrid ink, the Ag ratio (Ag/(Ag + Cu)) was controlled, and pure ACIGS without secondary phases was obtained. However, the ACIGS solar cells fabricated by this method had a conversion efficiency of only approximately 4% and relatively low shunt resistance (Rsh) and carrier concentration (∼1015/cm3). To improve the Rsh and carrier concentration, ACIGS was doped with Sb by mixing the Sb precursor into the hybrid ink. The Sb-doped ACIGS exhibited grain growth and grain boundary reduction without secondary phase formation. In addition, capacitance–voltage (C–V) measurements showed an increase in the carrier concentration (∼1016/cm3). Therefore, the conversion efficiency of Sb-doped ACIGS increased with increasing Rsh and open-circuit voltage (VOC).