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 degrees C in N-2 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.