Preparation and characterization of Cu(In,Ga)Se2 thin films via direct heating selenium-ion containing precursors

Polycrystalline Cu(In,Ga)Se2 thin films were synthesized as absorber layers in solar cells using a simple synthetic route. In this synthesis, selenium ion-containing precursors were heated in a reducing atmosphere to yield CIGS films instead of conventional heating in a selenium-containing atmosphere. Selenium ions were incorporated into the precursor films to form chalcopyrite-type CIGS films at comparatively low temperature (350 °C). As the heating temperature increased, the crystallinity and density of the formed CIGS films improved. The open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and conversion efficiency (η) of the prepared solar cells also substantially increased with the heating temperature. CIGS solar cells with absorber layers that had been heated at 550 °C exhibited a conversion efficiency of 8.27%. The corresponding values of Voc, Jsc, and FF were obtained as 0.452 V, 32.9 mA/cm2 and 55.5% respectively. The diode parameters were reduced and the external quantum efficiency (EQE) of the CIGS solar cells was improved by increasing the heating temperature. The photoluminescence peaks that were associated with the donor–acceptor pairs became weaker as the heating temperature increased. The suppression of electron–hole recombination led to improve the photovoltaic properties of the solar cells. This study demonstrates that directly heating selenium ion-containing precursors is an effective way to prepare highly efficient CIGS absorber layers for solar cells applications.