Quantitative Analysis of Trap-State-Mediated Exciton Transport in Perovskite-Shelled PbS Quantum Dot Thin Films Using Photocarrier Diffusion-Wave Nondestructive Evaluation and Imaging

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• 作者：Lilei Hu ; Zhenyu Yang ; Andreas Mandelis ; Alexander Melnikov ; Xinzheng Lan ; Grant Walters ; Sjoerd Hoogland ; Edward H. Sargent
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 7, 2016
• 年：2016
• 卷：120
• 期：26
• 页码：14416-14427
• 全文大小：704K
• 年卷期：0
• ISSN：1932-7455

文摘

Perovskite-shelled colloidal quantum dots (CQDs) with low trap-state density are promising candidates for large-scale, low-cost, and lightweight solar cell applications. However, even minimal trap states can significantly limit CQD-based solar cell efficiency. We reported trap-state-mediated exciton transports in methylammonium lead triiodide (MAPbI₃) perovskite-passivated PbS CQD thin films. Excitation power-dependent photocarrier radiometry (PCR) intensity study demonstrated the free (electrons/holes)-to-bound (acceptors/donors) and trap-state-related transition-induced nonlinear response of CQD thin films to excitation. The existence of shallow trap states (activation energy: 33.8–40.7 meV) was characterized using photothermal emission spectra at different modulation frequencies. CQD thin films were imaged, for the first time, by InGaAs-camera-based nondestructive homodyne and heterodyne lock-in carrierographies (LIC; spectrally gated dynamic photoluminescence imaging), clearly showcasing photocarrier density diffusion-wave inhomogeneities that stem from defect-associated multiple effective exciton lifetimes. PCR frequency scans, coupled with the trap-state-mediated exciton transport model, extracted multiple material and carrier transport parameters such as effective exciton lifetime τ_E, hopping diffusivity D_h, dark and bright state separation energy ΔE, and carrier trapping rate N_T. Camera-based contactless homodyne and heterodyne LIC imaging of QD thin films was found to be a promising nondestructive characterization technique for monitoring optoelectronic qualities of QD materials and devices.