Abstract
Amongst the many spectacular properties of hybrid lead halide perovskites, their defect tolerance is regarded as the key enabler for a spectrum of high-performance optoelectronic devices that propel perovskites to prominence. However, the plateauing efficiency enhancement of perovskite devices calls into question the extent of this defect tolerance in perovskite systems; an opportunity for perovskite nanocrystals to fill. Through optical spectroscopy and phenomenological modeling based on the Marcus theory of charge transfer, we uncover the detrimental effect of hot carriers trapping in methylammonium lead iodide and bromide nanocrystals. Higher excess energies induce faster carrier trapping rates, ascribed to interactions with shallow traps and ligands, turning these into potent defects. Passivating these traps with the introduction of phosphine oxide ligands can help mitigate hot carrier trapping. Importantly, our findings extend beyond photovoltaics and are relevant for low threshold lasers, light-emitting devices and multi-exciton generation devices.
Highlights
Amongst the many spectacular properties of hybrid lead halide perovskites, their defect tolerance is regarded as the key enabler for a spectrum of high-performance optoelectronic devices that propel perovskites to prominence
The photoluminescence quantum yield (PLQY) spectra plotted as a function of δE, known as ‘photo-action’ spectra, contain information on hot carrier effects: dynamic processes occurring during the relaxation of high-energy carriers to the band edge[32]
To delve deeper into the origins of this loss of carriers, we investigated the fate of the hot carriers using femtosecond transient absorption, namely PP, and PPP spectroscopy
Summary
Amongst the many spectacular properties of hybrid lead halide perovskites, their defect tolerance is regarded as the key enabler for a spectrum of high-performance optoelectronic devices that propel perovskites to prominence. LHP-based devices can achieve extraordinary performances despite possessing large densities of point defects These defects arise from solution-processing (about 1016 to 1017 cm−3 for thin films) and consist predominantly of shallow traps with a smaller population of deep trap sites[6,7,8]. After several years of relentless growth, efficiency enhancements in perovskite-based devices are reaching a plateau This calls for a more in-depth study of defects in LHPs, a reconsideration of the role of shallow traps and their bearing on defect tolerance[13]. Many of these applications rely on high-energy, nonresonant excitations, e.g., GaN back-illumination or high-energy charge injection (around 1 eV excess energy above the band-gap) in light-emitting devices, and violet/blue sunlight conversion in solar cells. The possibility of retaining high PLQY without extensive engineering of their surfaces, is the hallmark of a defecttolerant electronic structure[27,29]
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