Recombination by grain-boundary type in CdTe

Abstract

We conducted cathodoluminescence (CL) spectrum imaging and electron backscatter diffraction on the same microscopic areas of CdTe thin films to correlate grain-boundary (GB) recombination by GB “type.” We examined misorientation-based GB types, including coincident site lattice (CSL) Σ = 3, other-CSL (Σ = 5–49), and general GBs (Σ > 49), which make up ∼47%–48%, ∼6%–8%, and ∼44%–47%, respectively, of the GB length at the film back surfaces. Statistically averaged CL total intensities were calculated for each GB type from sample sizes of ≥97 GBs per type and were compared to the average grain-interior CL intensity. We find that only ∼16%–18% of Σ = 3 GBs are active non-radiative recombination centers. In contrast, all other-CSL and general GBs are observed to be strong non-radiative centers and, interestingly, these GB types have about the same CL intensity. Both as-deposited and CdCl2-treated films were studied. The CdCl2 treatment reduces non-radiative recombination at both other-CSL and general GBs, but GBs are still recombination centers after the CdCl2 treatment.

Defect Tolerance in as-deposited Selenium-alloyed Cadmium Telluride Solar Cells

“…Dark contrast is seen at the grain boundaries in the upper region of the bevel (the CdTe layer). This observation is consistent with previous CL measurements on non-alloyed CdTe devices and demonstrates that the grain boundaries act as recombination centres [5]. The behavior can be seen more clearly in the higher magnification image in Fig.…”

Radiative Efficiency and Charge‐Carrier Lifetimes and Diffusion Length in Polycrystalline CdSeTe Heterostructures

“…Here, we observe that the GB contrast is significantly lower than the contrast at the intragrain defects (IGDs). In polycrystalline CdTe, it is more typical to observe a larger GB contrast . The CL results suggest that IGDs in CdSeTe contribute significantly to nonradiative losses and that GBs are relatively benign.…”

Charged grain boundaries reduce the open-circuit voltage of polycrystalline solar cells—An analytical description

“…We restrict this work to grain sizes d which are greater than 2 W GB , so that the grain is not fully depleted. For a doping density 10 15 cm −3 this requirement implies d > 2 μ m. As a point of comparison, recent cathodoluminescence spectrum imaging 27 shows that the average grain size in CdTe thin films (excluding twin boundaries) is 2.3 μ m.…”