Effect of K Doping on the Performance of Aqueous Solution‐Processed Cu(In,Ga)Se2 Solar Cell

Abstract

Copper indium gallium selenide Cu(In,Ga)Se2 (CIGS) solar cells fabricated by vacuum thermal evaporation, magnetron sputtering, or organic solvent solution‐process either lead to high manufacturing cost and film nonuniformity or cause explosion, toxication and pollution. To address these issues, herein, water as a solvent to prepare the CIGS precursor solution is used and 7.04% efficient CIGS solar cells without MgF2 antireflection layer is obtained. Furthermore, for the first time, K doping on CIGS films via adding “K+” into the aqueous precursor solution is conducted. K–In–Se species is formed in the process of selenization and acts as a Se reservoir during CIGS grain growth, resulting in improved quality of the CIGS film with much larger grains. K doping can also inhibit the loss of Ga element. The high‐bandgap K–In–Se phase and higher Ga content combine to result in the increase in the CIGS bandgap. As a result, the K‐doped CIGS solar cell achieves a 33.1% enhancement in efficiency to 9.37%, with the significant increase in the open‐circuit voltage from 520.5 to 597.1 mV and fill factor from 50.77 to 55.36%. These results provide an important preliminary foundation for the development of aqueous precursor solution‐based CIGS solar cells.