Physical Origins of the Transient Absorption Spectra and Dynamics in Thin-Film Semiconductors: The Case of BiVO₄

Journal Article · Mon Aug 20 00:00:00 EDT 2018 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.8b06645· OSTI ID:1506360

Cooper, Jason K.  ^[1]; Reyes-Lillo, Sebastian E. ^[2]; Hess, Lucas H. ^[3]; Jiang, Chang-Ming ^[3]; Neaton, Jeffrey B. ^[4]; Sharp, Ian D.  ^[5]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis, Chemical Sciences Division
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry; Univ. of California, Berkeley, CA (United States). Dept. of Physics; Univ. Andres Bello, Santiago (Chile). Dept. de Ciencias Físicas
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry; Univ. of California, Berkeley, CA (United States). Dept. of Physics, and Kavli Energy NanoSciences Inst.
5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Artificial Photosynthesis, Chemical Sciences Division; Technische Univ. München, Garching (Germany). Walter Schottky Institut and Physik Dept.

Transient absorption (TA) spectroscopy is uniquely suited for understanding kinetic processes initiated by light over vast ranges of time. In combination with white light probes, the recorded differential absorption spectra can contain spectroscopic signatures characteristic of specific charge carrier population densities. However, disentangling the often-complex and convoluted spectra is made challenging without robust analysis methods relating the underlying physical mechanisms to the spectral components. In this work, we address the origin of the transient spectra of a model system of emerging solar energy harvesting materials using a monoclinic BiVO₄ thin film. Using ground-state optical properties of the semiconductor, we find the main derivative-like spectral response to be related to shifting and broadening of oscillators, rather than specific carrier-related transitions. However, by using the Drude optical model of free carriers, we also identify the transient response related to free-hole density. Importantly, sample heating from the optical pumping, which begins at ~10 ps and plateaus by ~200 ps, dominates the overall spectral response at longer times. On the basis of a physical model of the spectral response, a kinetic model is developed that describes the pump power dependence of the free-hole density, as well as the temporal evolution of the spectral changes associated with shifting and broadening of oscillators. First-principles density functional theory calculations are used to rationalize experimental measurements. Here, this comprehensive approach to analyzing and modeling the TA spectra offers a generalizable basis for understanding the complex pump-probe data, reveals thermal heating artifacts that are frequently erroneously assigned to long-lived photocarriers, and offers a path to eliminating ambiguity in analysis of photocarrier dynamics in solid-state systems.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
• Grant/Contract Number: AC02-05CH11231; SC0004993
• OSTI ID: 1506360
• Journal Information: Journal of Physical Chemistry. C, Vol. 122, Issue 36; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY