Enhanced Photovoltaic Performance of Heavy-Metal-Free AgInS₂ Quantum Dot-Sensitized Solar Cells Using a Facile SILAR Method

This study investigates the synthesis of heavy-metal-free AgInS₂ quantum dots (QDs) using a facile successive ionic layer adsorption and reaction (SILAR) method, exploring their application in quantum dot-sensitized solar cells (QDSSCs). The AgInS₂ QDs were grown on mesoporous TiO₂ via a two-stage SILAR process at room temperature. The optimization of Ag-S SILAR cycles (n) was performed to determine the ideal conditions, while the In-S SILAR cycles were held constant at seven cycles. X-ray diffraction (XRD) pattern analysis revealed an orthorhombic crystalline structure of the synthesized AgInS₂ QDs. Analysis of the optical spectra revealed a reduction in the optical energy bandgap (E_g,op) of AgInS₂ QDs from 2.00 eV to 1.92 eV and further to 1.78 eV as the value of n increased from 1 to 3. Employing AgInS₂ QDs, a polysulfide electrolyte, and a CuS counter electrode, liquid-junction semiconductor QDSSCs were fabricated. Optimal conditions were achieved at n = 2, resulting in outstanding power conversion efficiency (PCE) of 3.57% (J_sc = 8.56 mA/cm², V_oc = 0.64 V, FF = 65.2%). Under reduced light intensity (0.25 sun), the PCE increased to 5.26%. The external quantum efficiency (EQE) spectrum of the best cells spanned 400−700 nm, maintaining a nearly constant EQE value of ~ 65% within the 400−600 nm range. Remarkably, the PCE achieved surpassed previously reported liquid-junction AgInS₂ QDSSCs. These findings highlight the facile production of heavy-metal-free AgInS₂ QDs through a room-temperature SILAR method and the tunable optical properties of AgInS₂ QDs by controlling Ag-S SILAR cycles, revealing their potential as an efficient solar absorber.