Cation‐Exchange Synthesis of Highly Monodisperse PbS Quantum Dots from ZnS Nanorods for Efficient Infrared Solar Cells

Abstract

Infrared solar cells that utilize low-bandgap colloidal quantum dots (QDs) are promising devices to enhance the utilization of solar energy by expanding the harvested photons of common photovoltaics into the infrared region. However, the present technology for synthesis of PbS QDs cannot produce highly efficient infrared solar cells. Here, we develop a general synthesis framework for low-bandgap PbS QDs (0.65-1 eV) via cation-exchange from ZnS nanorods (NRs). First, ZnS NRs are converted to superlattices with segregated PbS domains within each rod. Then, sulfur precursors are released via dissolution of the ZnS NRs during the cation-exchange, which promotes size-focusing of PbS QDs. PbS QDs synthesized through this new method have the advantages of high monodispersity, ease of size control, in-situ passivation of chloride, high stability, and "clean" surface. We fabricated infrared solar cells based on these PbS QDs with different bandgaps, using conventional ligand exchange and device structure. All of our devices produced in this manner show excellent performance, showcasing the high quality of our PbS QDs. The highest performance of infrared solar cells was achieved using ~0.95 eV PbS QDs, exhibiting an efficiency of 10.0% under AM 1.5 solar illumination, a perovskitefiltered efficiency of 4.2% and a silicon-filtered efficiency of 1.1%.

PbS Colloidal Quantum Dot Inks for Infrared Solar Cells

“… (C) Light absorption spectra of CQDs with different dot sizes. Adapted with permission from Xia et al. (2019) .…”

“…Other synthetic methods, such as biomineralization ( Spangler et al., 2016 ) and ion exchange, were also studied for the synthesis of CQDs. Xia et al. (2019) demonstrated that the CQDs could be synthesized from ZnS nanorods using a cation exchange approach and the resulted CQDs had a low infrared E g .…”

Efficient Infrared Solar Cells Employing Quantum Dot Solids with Strong Inter‐Dot Coupling and Efficient Passivation

“…As a result, the PbSe/PbS QD IR solar cells focusing on a bandgap of ≈0.95 eV produce a high V OC which is 1.46 times that of pristine PbSe QD devices due to the improved surface passivation. Furthermore, the PbSe/PbS QD devices demonstrate a much higher IR J SC compared to the previously reported PbS QD devices [ 1,3,4,8,9,20,21 ] due to the strong electronic coupling among adjacent QDs. Consequently, we achieved a high Si‐filtered PCE of 1.24% without any light trapping nanostructure.…”

“…Matching the absorption spectrum of cSi with the solar spectrum ( Figure a), the short‐wavelength infrared (IR) (>1100 nm) photons which occupy approximately 20% of the whole sun's power reaching the Earth's surface are unavailable for cSi solar cells due to its indirect large bandgap of ≈1.1 eV. [ 1,3 ] Thus, it is a promising avenue to harvest these high transmissible low energy photons (<1.1 eV) for breaking through the efficiency limitation. Theoretical calculation has predicted that up to 6% extra power points can be appended to the Si‐based solar cells via cascading IR solar cell to collect the photons beyond 1100 nm of sunlight.…”

“…To address this problem, we developed a strategy via combination of epitaxially coating a thin PbS shell over the PbSe core QDs and in situ halide passivation in the present work. Cation exchange synthesis [ 3 ] was adopted to grow the PbS shells with in situ halide passivation that protects the PbSe QDs, giving rise to excellent trap‐state control and simultaneously obtaining the superior strong inter‐dot coupling and carrier transport. As a result, the PbSe/PbS QD IR solar cells focusing on a bandgap of ≈0.95 eV produce a high V OC which is 1.46 times that of pristine PbSe QD devices due to the improved surface passivation.…”