Optoelectronic and material properties of nanocrystal-based CZTSe absorbers with Ag-alloying

In this work, the benefits of Ag-alloying in kesterite solar cells are explored in terms of tunable band gap, improved grain growth, improved minority carrier lifetime, reduced defect formation, and reduced potential fluctuations for (Ag,Cu)2ZnSnSe4 (ACZTSe) absorbers relative to Cu2ZnSnSe4 (CZTSe). The enhanced optoelectronic properties are shown to scale here with the degree of Ag-alloying in ACZTSe. The impacts of these effects on device performance are discussed, with improvement in average device performance/open-circuit voltage reported for ACZTSe (5%-Ag) absorbers relative to CZTSe absorbers with similar band gap. These initial results are promising for the Ag-alloyed ACZTSe material system as VOC limitations are the primary cause of poor device performance in kesterite solar cells, and cation substitution presents a unique method to tune the defect properties of kesterite absorbers. Herein, nanoparticle synthesis and large-grain ACZTSe absorber formation is described followed by material and optoelectronic characterization. Additionally, RTP processing is presented to achieve fully selenized large-grain chalcogenide absorbers from sulfide nanocrystal inks.