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

Copper indium gallium selenide Cu(In,Ga)Se 2 (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 MgF 2 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.