Pb-Free Infrared Harvesting Colloidal Quantum Dot Solar Cells Using n-p Homojunction Architecture

Harvesting infrared (IR) sunlight using colloidal quantum dots (CQDs) holds significant promise for optoelectronic devices including photovoltaics (PVs) and self-powered sensors. Traditionally, Pb chalcogenides have been utilized in energy devices, but needs for RoHS compliance derive the development of Pb-free alternatives. A key challenge with Pb-free materials is the low photovoltage in devices, primarily due to recombination in surface defects and interfaces within the architectures. Here, the Pb-free CQD PVs capable of harvesting the IR light beyond the Si PVs are first presented. Designing an InAs CQD-based homojunction architecture, with n-type InAs absorbers passivated with multifunctional ligands and p-type conductive InAs inks, efficient charge extraction is achieved while suppressing interface recombination. Additionally, the IR light path is modulated to match the absorber's absorption to optimize the performance. This led to InAs PVs with absorber bandgaps ranging from 1.35 to 1.03 eV, significantly improving the open-circuit voltage from 0.05 to 0.26 V and fill factor from 29% to 50%, comparable to Pb-based PVs. The InAs IR-PVs exhibit a power conversion efficiency of 2.00% under one-sun and 0.27% with a Si filter, outperforming control ones (0.28% and 0.03%). This work provides an effective strategy for designing Pb-free, energy-independent IR optoelectronics.