Superstrate-type photovoltaics with copper indium sulfide (CuInS2) fabricated by solution processes: correlation between interfacial charge transfer and solar cell performance

Copper indium sulfide, CuInS 2 (CIS) semiconductors have currently attracted a great deal of attention as photosensitizers for solar cells. In this study, CIS/CdS/TiO 2 solar cells were prepared by a simple, low-cost, and non-vacuum process. In particular, sandwich-type solar cells were fabricated using conductive carbon as hole transport layers (HTL) and/or ohmic contacts. Superstrate-type CIS/CdS/TiO 2 solar cells were constructed with titanium dioxide (TiO 2 ), cadmium sulfide (CdS), and CIS, of which the interfacial interaction could be expected to form an effective p-n junction. The photovoltaic performance was optimized by investigating the preparation conditions, i.e., the TiO 2 blocking layers, chemical bath deposition (CBD) of CdS, and differing Cu/In composition ratios of CIS. When the composition ratio of Cu/In was 1.1 (Cu-rich), the optimal photoconversion efficiency (PCE) of the solar cell was achieved at 4.87%. The relationship between electrochemical impedance and solar cell performance was also clarified. The present results revealed that a low impedance for the charge transfer in the bulk and interface improved solar cell performance. Graphical abstract