Indium-Rich AgInS₂–ZnS Quantum Dots—Ag-/Zn-Dependent Photophysics and Photovoltaics

Abstract

AgInS2–ZnS solid solution quantum dots (QDs) prepared with varying Ag/Zn ratios demonstrate composition-dependent photophysical properties. Absorption and emission processes are extremely complex in these compounds because of easily formed crystallographic defects which serve as intraband gap states and provide additional excitation and relaxation pathways. In addition to valence to conduction band absorption, defect states located within the band gap are responsible for tail absorption in these nanoparticles and are assigned to AgIn antisite defects. These AgInS2–ZnS QDs display wavelength-dependent photoluminescence (PL) decays along with large Stokes shifts and long PL lifetimes, strongly suggesting that donor–acceptor pair recombination is the dominant radiative pathway. The excited-state interaction between AgInS2–ZnS and TiO2 is studied through the use of transient absorption spectroscopy, and a fast photoinduced electron-transfer rate constant of 5 × 1011 s–1 is determined. This interaction with TiO2 is further probed by testing various compositions of AgInS2–ZnS in liquid-junction solar cells, with the optimum device power conversion efficiency reaching 1.83%.