Ultrafast Carrier Dynamics of CdTe: Surface Effects

Abstract

Cadmium telluride has been an important absorber material used in solar cells for decades given its near-optimum band gap and lower cost for device fabrication. However, the overall efficiency has been low compared to the theoretical limit. One major contributor to the problem of the relatively low open-circuit voltage is the high surface recombination of photogenerated carriers. In this contribution, time-resolved pump–probe reflectivity was used to study the carrier dynamics of CdTe(111) under the influence of selected surface conditions. It was found that surfaces after the processes of chemical etching and thermal oxidation for short durations exhibit bulk-like transient reflectivity and a clearly reduced surface recombination velocity, according to a model calculation. The comparative study indicates that the origins of carrier traps include the midgap defect states that are associated with the uncapped Te surface atoms, namely the Te antisites and Te interstitials, and subsurface damages resulting from polishing and ion sputtering. The present results suggest that the formation of a thin oxide layer through annealing after chemical etching may be beneficial for surface improvement for CdTe-based solar cells.

SnO2-Catalyzed Oxidation in High-Efficiency CdTe Solar Cells

“…On the topic of whether oxygen alone can chemically passivate CdTe, theory and experiment are somewhat at odds. A recent transient reflectivity study of single crystal CdTe indicates that surface oxidation can reduce tellurium-related defects and increase carrier lifetimes . Several older works also appeared to show that CdTe oxides could passivate CdTe surfaces. ,, A first principles investigation of oxygen adsorption on CdTe(110) indicated, however, that oxygen increased the number of mid-gap surface states …”

Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS2

“…Experimental details about the reflection UED and optical transient reflectivity measurements have been described previously. , In short, the 515 nm, 2.41 eV photoexcitation pulses with a repetition rate of 2 kHz were produced by the second harmonic generation of the fundamental output (1030 nm) of a Yb:KGW regenerative amplifier laser system. The photoexcitation beam was loosely focused on the specimen surface at a near-normal incidence angle, resulting in a footprint of ∼600 μm in the full width at half-maximum (fwhm).…”

Breaking AgInTe2 Quantum Dot Chain to Fabricate AgInTe2–ZnS Janus Nanocrystals

“…Therefore, further property deterioration due to long-term exposure does not happen in most of the cases. , However, there are a few exceptions to this, in which surface oxidation does not stop at least up to two years of experimental observation . While this kind of controlled oxidation on the clean surface leads to superior charge carrier dynamics in a few cases such as CdTe, , it also leads to nonradiative charge recombination and compromised optical properties in Te-based I–III–VI MnCs. ,, To mitigate the adverse effect of surface oxidation, researchers prepared core–shell and alloyed MnCs, but the result could not meet the expectations completely. − While zero-dimensional QDs may offer a way to study the surface oxidation behavior of these Te-based MnCs due to their large surface-to-volume ratio, to the best of our knowledge, no QD structure of AgInTe 2 has been reported to date. This is in sharp contrast to other chalcogens of I–III–VI MnCs where the relevant QDs are reported. − This is possibly because AgInTe 2 MnCs tend to form a 1-D anisotropic (nanowire, nanotube, or nanobelt) structure via self-assembly, even in the absence of any seed or surfactant .…”