CsPbBr₃ Nanocrystal Films: Deviations from Bulk Vibrational and Optoelectronic Properties

Abstract

Metal-halide perovskites (MHP) are highly promising semiconductors for light-emitting and photovoltaic applications. The colloidal synthesis of nanocrystals (NCs) is an effective approach for obtaining nearly defect-free MHP that can be processed into inks for low-cost, high-performance device fabrication. However, disentangling the effects of surface ligands, morphology, and boundaries on charge-carrier transport in thin films fabricated with these high-quality NCs is inherently difficult. To overcome this fundamental challenge, terahertz (THz) spectroscopy is employed to optically probe the photoconductivity of CsPbBr 3 NC films. The vibrational and optoelectronic properties of the NCs are compared with those of the corresponding bulk polycrystalline perovskite and significant deviations are found. Charge-carrier mobilities and recombination rates are demonstrated to vary significantly with the NC size. Such dependences derive from the localized nature of charge carriers within NCs, with local mobilities dominating over interparticle transport. It is further shown that the colloidally synthesized NCs have distinct vibrational properties with respect to the bulk perovskite, exhibiting blue-shifted optical phonon modes with enhanced THz absorption strength that also manifest as strong modulations in the THz photoconductivity spectra. Such fundamental insights into NC versus bulk properties will guide the optimization of nanocrystalline perovskite thin films for optoelectronic applications.

Environment-Induced Reversible Modulation of Optical and Electronic Properties of Lead Halide Perovskites and Possible Applications to Sensor Development: A Review

“…Under appropriate synthesis conditions, colloidal lead halide nanocrystals can be obtained in solutions and nanocrystal (NC) films can be deposited onto substrates by means of drop-casting or spin-coating. [ 15 , 16 ].…”

Ambipolar Passivated Back Surface Field Layer for Silicon Photovoltaics

“…[1][2][3][4][5] For example, the surface defects in transistors act as recombination centers for carriers, leading to degradation of electrical properties including dispersion of transconductance, undesirable hysteresis, and low breakdown voltages period. [6][7][8] In light-emitting devices, free charges trapped in the defect states cause nonradiative recombination and hinder the charge transport, thereby lowering the photoluminescence quantum yield. [9][10][11] yielded PCEs up to ≈17% [40][41][42][43][44] In addition, additional doping processes or high-temperature vacuum processes involving the deposition of a-Si:H on the rear-side of Si are usually adopted to enhance the cell performance.…”

“…[ 1–5 ] For example, the surface defects in transistors act as recombination centers for carriers, leading to degradation of electrical properties including dispersion of transconductance, undesirable hysteresis, and low breakdown voltages period. [ 6–8 ] In light‐emitting devices, free charges trapped in the defect states cause non‐radiative recombination and hinder the charge transport, thereby lowering the photoluminescence quantum yield. [ 9–11 ] Likewise, in Si‐based solar cells, defects or dangling bonds on the surface cause severe recombination, which lowers minority carrier lifetime and deteriorates photovoltaic parameters, including open‐circuit voltage ( V oc ), short‐circuit current ( J sc ) and fill factor ( FF ).…”

Carrier and exciton dynamics in halide perovskites

“…The obtained recombination rate constants increase with decreasing NC size which is attributed to the stronger overlap of electron and hole wave functions caused by the confinement e↵ect [64]. The calculated e↵ective mobility µ decreases with increasing NC size, revealing the localized nature of the photogenerated carriers when CsPbBr 3 goes from bulk to quantum dots [65].…”

“…Clinquanta et al measured a 3-µm thick CsPbBr 3 and obtained a strong peak shift of ⇠1.7 meV for the phonon mode at ⇠3.5 meV (⇠28 cm 1 ). Note that for typical bulk CsPbBr 3 , the THz absorption spectrum shows a broad peak centered around 2.3 THz[65]. What Clinquanta et al used is CsPbBr 3 in low dimension[101] which I will describe in Chapter 6.…”