Optoelectronic Characterization of Emerging Solar Absorber Cu3AsS4
Scott A. McClary1, Siming Li2, Xinxing Yin3, Patricia Dippo4, Darius Kuciauskas4, Yanfa Yan3, Jason B. Baxter2, Rakesh Agrawal1
1Purdue University, West Lafayette, IN, United States
/2Drexel University, Philadelphia, PA, United States
/3University of Toledo, Toledo, OH, United States
/4National Renewable Energy Laboratory, Golden, CO, United States

Cu3AsS4 in the enargite (ENG) crystal structure has recently been identified as a promising material for thin-film PV applications. However, the performance of devices has so far been poor. To decouple the effects of material properties and device architecture on the solar cell performance, we present the results of optoelectronic characterization on thin films of ENG derived from nanoparticle precursors.  Photoluminescence (PL) spectroscopy was used to study the electronic structure at room temperature and 4.25 K. The results suggested that low concentrations of shallow defects are present in ENG, which is promising for electron and hole transport through the material. Time-resolved terahertz spectroscopy (TRTS) was used to probe the carrier dynamics within Cu3AsS4. At high-injection conditions, radiative or Auger (rather than Shockley-Read-Hall) dominates the recombination kinetics with time constants of 1.8 and 1.6 ns, respectively. At lower injection levels closer to PV operation, the SRH recombination rate may become more important, but the SRH carrier lifetimes are at least on the order of ns. With promising defect characteristics and carrier dynamics, it is likely that the currently used device architecture is detrimental to ENG-based solar cell performance. Cyclic voltammetry measurements were performed to estimate the band edges of ENG, and the results indicated a severe cliff offset with CdS that induces significant interface recombination. One promising n-type layer to pair with ENG is ZnS, which results much more favorable interface properties and a SCAPS-simulated efficiency nearing 20% using currently measured material properties.  These results suggest that Cu3AsS4 is worthy of further research efforts, particularly in the development and optimization of novel device architectures.