Improved Performance of CuInS2 Quantum Dot-Sensitized Solar Cells Based on a Multilayered Architecture

This article describes a CuInS2 quantum dot (QD)-sensitized solar cell (QDSSC) with a multilayered architecture and a cascaded energy-gap structure fabricated using a successive ionic-layer adsorption and reaction process. We initially used different metal chalcogenides as interfacial buffer layers to improve unmatched band alignments between the TiO2 and CuInS2 QD sensitizers. In this design, the photovoltaic performance, in terms of the short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE), was significantly improved. Both JSC and VOC were improved in CuInS2-based QDSSCs in the presence of interfacial buffer layers because of proper band alignment across the heterointerface and the negative band edge movement of TiO2. The PCE of CuInS2-based QDSSCs containing In2Se3 interfacial buffer layers was 1.35%, with JSC=5.83 mA/cm2, VOC=595 mV, and FF=39.0%. We also examined the use of alternative CdS and CdSe hybrid-sensitized layers, which were sequentially deposited onto the In2Se3/CuInS2 configuration for creating favorable cascaded energy-gap structures. Both JSC (11.3 mA cm(-2)) and FF (47.3%) for the CuInS2/CdSe hybrid-sensitized cells were higher than those for CuInS2-based cells (JSC=5.83 mA cm(-2) and FF=39.0%). In addition, the hybrid-sensitized cells had PCEs that were 1.3 times those of cells containing identically pretreated In2Se3 interfacial buffer layers. Additionally, we determined that ZnSe served as a good passivation layer on the surface of CuInS2/CdSe hybrid-sensitized QDs, prevented current leakage from the QDs to electrolytes, and lowered interfacial charge recombination. Under simulated illumination (AM 1.5, 100 mW cm(-2)), multilayered QDSSCs with distinct architectures delivered a maximum external quantum efficiency of 80% at 500 nm and a maximum PCE of 4.55%, approximately 9 times that of QDSSCs fabricated with pristine CuInS2.