Charge carrier mobilities and dynamics in thin film compound semiconductor materials from transient Thz absorption

Abstract

We use optical pump Thz probe spectroscopy to access the microscopic mobilities and fast charge carrier dynamics processes in polycrystalline chalcopyrite and kesterite thin films grown by coevaporation. In order to avoid complicating effects from the presence of Ga-gradients, ternary CuInSe 2 samples were used as a model system. Significantly different DC mobilities were found for stoichiometric and Cu-poor samples, respectively. While the stoichiometric samples exhibit Drude-like free carrier mobilities with DC mobilities up to 1200cm 2 /Vs at room temperature, the Cu poor samples show non-Drude behavior, with much lower DC mobilities, indicative of carrier localization. Kesterite materials are found to show even stronger signatures of carrier localization than the chalcopyrites.

Effects of Thermochemical Treatment on CuSbS2 Photovoltaic Absorber Quality and Solar Cell Reproducibility

“…This difference can be attributed to the Sb p-states at the conduction band minimum (CBM) of CuSbS 2 , compared to the In s-states at the CBM on CuInS 2 . Also, the absolute mobility determined here for our CuSbS 2 samples (4 cm 2 /(V s)) is much lower than that for high-quality CIGS samples (up to 1200 cm 2 /(V s)) …”

“…Also, the absolute mobility determined here for our CuSbS 2 samples (4 cm 2 /(V s)) is much lower than that for high-quality CIGS samples (up to 1200 cm 2 /(V s)). 50 Another important factor that sets the layered CuSbS 2 aside from the multinary tetrahedrally bonded semiconductors is the large structural difference between the tetrahedral Cu sites and the distorted octahedral-like Sb sites. This difference makes CuSbS 2 less prone to cation disorder on the tetrahedral sites, and the band tailing or potential fluctuations that can result from such disorder.…”

Lateral Charge Carrier Transport in Cu(In,Ga)Se2 Studied by Time‐Resolved Photoluminescence Mapping

“…Absorber compositions with higher Ga-content may result in higher densities of point defects in the grain interiors, [41,42] and result in lower mobilities due to the expected alloy or impurity scattering as compared with those found in previous studies. [4,26] This is not necessarily the case for steel sample, which has the lowest bandgap-thus Ga content-(see Table S1, Supporting Information), and the lowest mobility of all samples studied. We estimate for sample steel a mobility range of about half of the values of the SLG samples.…”

“…A large variety of measurement systems were used to characterize recombination and carrier transport properties such as carrier lifetime, [2,3] mobility, [4] diffusion length, [5][6][7][8] and even access to diode parameters: [9] cathodoluminescence, [10] electroluminescence, [11] steady-state photoluminescence (PL), [12,13] time-resolved THz spectroscopy, [4,14] time of flight (ToF), [15] time-resolved microwave conductivity (TRMC), lock-in thermography, [16] laser-beaminduced current (LBIC), [16] electron-beam-induced current (EBIC), [17,18] two-photon spectroscopy, [19] and transport imaging (scanning electron microscopy [SEM] coupled to a microscope and camera). [20] Usually, more than one technique is required to determine the charge carrier lifetime or mobility.…”

Observation of Space Charge Dynamics Inside an All Oxide Based Solar Cell

“…The way of charge carrier generation and trapping processes are a subject of intense research in many third-generation solar cell materials . The basic mechanisms behind the photovoltaic effect are carrier generation due to absorption of photon, separation of the photogenerated charge carriers, and collection of these carriers at the terminals of the junction. , Processes of charge carrier excitation and transport occur in nanostructures due to their low dimensionality and the large surface-to-volume ratio. − Several spectroscopic techniques have enhanced the understanding of the charge carrier dynamics in semiconducting materials. − Extensive literature already exists on carrier dynamics in semiconductors, which describe many methods such as electrochemical, spectroelectrochemical, emission and transient absorption, etc . to investigate the photoinduced charge transfer process.…”