Charles J. Hages

Quantifying rates of charge carrier recombination is a crucial step in developing solar cells with high power conversion efficiencies. However, recovering characteristic parameters such as carrier mobility, doping concentration, and recombination rate constants is hindered by the interplay of the carrier dynamics with multiple recombination mechanisms. Interpretation of optoelectronic measurements, such as time-resolved photoluminescence (TRPL), usually relies on analytically tractable simplifications to the underlying physics models for carrier mobility and recombination, which sacrifices some of the information content of the measurement. We have recently shown that, by incorporating simulations of the complete carrier physics into a Bayesian analysis, previously unrecoverable material parameters, such as carrier mobility and the doping level, can be determined from TRPL measurements. Unfortunately, the large number of simulations required by a random sampling of the parameter space necessitated access to high-performance computing resources, limiting the usefulness of the approach. Here, we introduce an importance sampling algorithm (Metropolis Monte Carlo), which reduces the computational requirements by 2–3 orders of magnitude, rendering the Bayesian inference tractable on desktop computers. These developments affirm the utility of a simulation-driven analysis of optical characterization measurements, and make a physics-informed Bayesian inference available to all semiconductor researchers.

Remarkable progress in photovoltaic has been made by the halide perovskites, paving the way for overcoming the Shockley-Queisser-limit of 33.7 % of a single junction solar cell by in tandem photovoltaic applications. However, the biggest challenge for the commercialization is the stability of the halide perovskites which are rather prone to degradation through air, light, heat, and electric field mechanisms. Alternatively, highly stable chalcogenide perovskite materials, containing S, Se instead of halides might maintain their remarkable optoelectronic properties. Among these materials, BaZrS3 with a bandgap of around 1.9 eV and strong absorption coefficient attracts most attention due to the possible integration as a top cell in tandem applications. However, the biggest hurdle seems to be the synthesis of these materials at moderate temperatures on conductive substrates in order to get phase-pure material. Here, we investigate the formation of secondary phases in the low-temperature synthesis of BaZrS3 at 550 °C, compatible with device integration, with various annealing durations. Raman analysis reveals secondary phases such as BaS3 and ZrS3 which cannot be readily identified from X-ray diffraction. Longer annealing times improve the phase purity of BaZrS3.

Chalcogenide perovskites constitute a promising earth-abundant, non-toxic, and robust semiconductor family with the potential to compete with hybrid perovskites as high-quality photovoltaic absorbers. However, a low-temperature, solution-based synthesis route has eluded researchers in this area. Here we report the colloidal synthesis of chalcogenide perovskite BaZrS₃ nanoparticles at 330 °C in organic solvent. The nanoparticles (10-20 nm) are found to be comprised of smaller (3-5 nm) crystalline domains. Promising optoelectronic properties for the nanoparticles are measured, with photoluminescence decay times as high as 4.7 ns.

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal‐halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.