DFT investigation into the underperformance of sulfide materials in photovoltaic applications

Photoactive sulfide materials typically under-perform with respect to their theoretical maximum photovoltaic efficiency compared to other light absorbing solids. In an effort to reveal the underlying cause of this situation, we investigate several potential back contact metals for photovoltaic devices using the principles of band alignment; principles that have repeatedly shown to be of key importance in this field. Specifically, the sulfides SnS, CuInS₂ and Cu₂ZnSnS₄ are studied in contact with the metals Mo, Sn, Ti, W and Zr and their common terminations. We also consider the stability with respect to interfacial chemical degradation and show that almost all systems used to date are likely to form interstitial two-dimensional metal disulfides at the heterojunction interface. The likely effects of these disulfide secondary phases are explored and the optimal configurations for each photoactive sulfide presented.