Defect-State Transition Associated Hole Dynamics in Cuprous Iodide Nanosheets

Abstract

The cuprous iodide of zinc-blende structure (γ-CuI) is a p-type semiconductor with a wide band gap of 3.1 eV. It is considered promising as the third generation of semiconductors, in applications of hole transport layer and transparent electrode due to the high hole density and carrier mobility, but its carrier transport characteristics have not yet been understood in detail. We synthesized γ-CuI nanosheets with large sizes and measured the carrier dynamics by femtosecond transient absorption (TA) spectroscopy. We observed signals of defect trapping photogenerated carriers during band-edge transitions, as well the weak band filling and photoinduced absorption directly associated with defect states. The species and lifetimes of defect assisted transition are identified and quantified based on TA measurements with various excitation fluences, and the changes of spectra and kinetics of defect band filling are correlated to the trend of density of Cu and I vacancies in samples with different thicknesses, based on the observations on a single nanosheet. We extract a diffusion coefficient of ∼71 cm 2 s −1 and derive a diffusion length longer than the sample thickness, which possibly makes a remarkable contribution to the generation of a photocurrent. Our findings are expected to offer help for harnessing the defects in γ-CuI and improving its performances in optoelectronic applications.

CuI/BaSnO3 Quantum Dot/ZnSnO3 Perovskite-based Transparent p–n Junction for Photovoltaic Enhancement

“…CuI/ZSO-BSO-2 exhibited a photovoltaic enhancement of ∼2.6 × 10 3 folds, with a slight decrease in transparency of ∼5–7%. This indicates that the regulation of carrier behavior by the homologous perovskite BaSnO 3 QD’s transition layer is more important than simple absorption. − The homologous perovskite BaSnO 3 QD at the interface of CuI/ZnSnO 3 act as a ladder to promote the transfer of photo-generated carriers while maintaining decent transparency and increasing carrier injection through their high QY. , Additionally, Cu vacancies induce hole-related carriers, optimizing the intrinsic defects. − The synergistic effects of appropriate Fermi level, high QY of homologous perovskite BaSnO 3 QD, and p-type carrier induced by Cu vacancies enable the achievement of a favorable kinetic equilibrium for high PCE. ,− , Therefore, by modifying with the dual-functional homologous perovskite BaSnO 3 QD, the CuI/BaSnO 3 QD/ZnSnO 3 obtains a decent balance between PCE and transparency. − , Additionally, the excellent physical–chemical stability of inorganic perovskite BaSnO 3 QD and ZnSnO 3 contributes to the overall stability. − ,− …”

“…Notably, Zhang et al synthesized a large-sized transparent conductive CuI film using defect−state transition carrier dynamics. 34 Furthermore, the environmental nontoxicity and ease of synthesis are additional factors that contribute to the appeal of CuI as a p-type semiconductor. 35 For all these reasons, the wide bandgap of transparent devices remains a major constraint for achieving high photovoltaic conversion, primarily due to decreased carrier transport caused by excessive potential barriers.…”

“…Notably, Zhang et al. synthesized a large-sized transparent conductive CuI film using defect–state transition carrier dynamics . Furthermore, the environmental nontoxicity and ease of synthesis are additional factors that contribute to the appeal of CuI as a p-type semiconductor …”

A Droplet Method for Synthesis of Multiclass Ultrathin Metal Halides

“…The as‐synthesized 2D metal halide nanosheets are further investigated by X‐ray diffraction (XRD) and photoluminescence (PL) characterizations. Referring to Portable Document Format (PDF) Cards (Figure S3, Supporting Information) and previous studies, [ 12,31,32 ] the atomic structures of these 2D metal halides can be classified into three types: trigonal, hexagonal, and cubic phases. The sharp XRD peaks demonstrate good crystallinity of these nanosheets (Figure 1c).…”

“…[11] CuI has been investigated for use in flat panel displays, thermoelectric, flexible transparent p-n diodes, hole transport layers in solar cells, and self-powered photodetectors. [12,13] Metal halides exhibit attractive properties, therefore, which are desirable when entering into the family of 2D materials.…”