Influence of Processing Conditions on the Performance of Cu₂ZnSnS₄ Nanocrystal Solar Cells

Quaternary Cu₂ZnSnS₄ is a promising solar cell material because of its narrow band gap, high light absorption coefficient, and low cost. It is known that the composition of Cu₂ZnSnS₄ largely influences the solar cell performance. Here, to study the composition dependent properties of Cu₂ZnSnS₄ NCs as a solar cell material, we synthesized oleylamine-capped Cu₂ZnSnS₄ NCs with different compositions by a one-pot solution process, and fabricated solar cells with a ITO/ZnO/CdS/Cu₂ZnSnS₄/Au structure, and photoelectrochemical cells. A photovoltaic device using Cu₂ZnSnS₄ NCs with Cu/ (Zn + Sn)=0.87 showed the best performance among the devices tested. To improve the performance, the NC film fabrication processes were modified. We found that ligand stripping with BF₃:OEt₂ and the subsequent annealing at 250 °C in N₂ improved the power conversion efficiency from 0.06 to 0.14 %, most likely due to efficient stripping of surface insulating organic layers. The photocurrent response of a photoelectrochemical cell using the Cu₂ZnSnS₄ NCs deposited on a ITO substrate was also improved by the modified NC film fabrication processes.