Cu‐Rich Precursors Improve Kesterite Solar Cells

Abstract

A precursor‐annealing process based on a Cu‐rich precursor that has a maximum power conversion efficiency of 7.5% for pure selenide kesterite cells is presented. The Cu‐rich step is beneficial for the transport properties. Nanometer‐sized domains of ZnSe are found in all films.

Formation of nanometer-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films and their effect on solar cell efficiency

“…Mousel et al [20] attributed this observation to the Cu-rich nature of the precursor. It was shown that due to the incorporation of Sn the overall composition (measured by EDX) shifts from Cu-rich to Cu-poor.…”

“…In a previous work [20] the present authors detected a Cu-rich surface on the Cu-rich precursor by SIMS depth profiling and found indications for the formation of a Cu-Se phase. However, the distribution of this phase on the sub-micrometer scale was not studied in detail.…”

“…For Cu(In,Ga)Se 2 it was shown that a Cu-rich ([Cu]/([Ga]þ[In])>1) composition for a limited time during the growth process is beneficial for the cell performance due to an increase in grain size and a reduction in recombination activity [18,19]. In a previous work we could demonstrate that the Cu-rich growth step for CZTSe can be easily implemented by using a Curich precursor [20]. The Cu excess leads to the formation of Cu 2-x Se at the surface of the Cu-rich precursor, which can be removed by KCN etching.…”

“…Using secondary ion mass spectrometry (SIMS), Mousel et al [20] detected a Sn-enrichment at the surface of the annealed precursor, which suggested the formation of a Cu-Sn-Se compound, whereas Wang et al [24] detected Cu-Sn-S compounds at the CZTS/ Mo interface by EDX.…”

“…Mousel et al [20] and Wang et al [24] prepared precursors by a low temperature (320 C and 110 C, respectively) co-evaporation process and applied a post-deposition annealing process in a SnSe þ Se atmosphere and in a S atmosphere, respectively. Using secondary ion mass spectrometry (SIMS), Mousel et al [20] detected a Sn-enrichment at the surface of the annealed precursor, which suggested the formation of a Cu-Sn-Se compound, whereas Wang et al [24] detected Cu-Sn-S compounds at the CZTS/ Mo interface by EDX.…”