CdCl₂ Treatment-Induced Enhanced Conductivity in CdTe Solar Cells Observed Using Conductive Atomic Force Microscopy

Abstract

The rear surfaces of CdTe photovoltaic devices without back contacts, grown by close-spaced sublimation (CSS), were analyzed using conductive atomic force microscopy (C-AFM). As-deposited and CdCl-treated CdTe samples were compared to clarify the effect of the treatment on charge flow through grains and grain boundaries. The CdCl-treated samples exhibit a more homogeneous and enhanced current flow across the grains as compared to the as-deposited samples. The grain boundaries show variable current. Under high bias, grain boundaries dominate current flow when the main junction is reverse biased and with the conducting current in reverse breakdown. Under the opposite bias conditions, where the contact of the conductive tip to the surface is reverse biased and under breakdown conditions, the current flow is uniform with little contrast between grains and grain boundaries. The results are interpreted as resulting from the improved crystallinity of the CdTe with reduced p-type doping along the grain boundaries.

Spin-orbit coupling effects on predicting defect properties with hybrid functionals: A case study in CdTe

“…These conditions correspond to typical processing protocols for a CdCl2 treatment. [50,51] Note that the Cd3Cl2O2 phase imposes a tighter constraint to ∆ LO than CdCl2, thereby supporting the conclusion of Ref. [52] that this ternary phase acts as the major chlorine-containing component under the actual process conditions.…”

Charged Grain Boundaries and Carrier Recombination in Polycrystalline Thin-Film Solar Cells

“…A direct analytical solution for the full two-dimensional problem is not feasible. To make analytical progress, we split the two-dimensional system into two onedimensional sub-systems: the grain boundary core where electrons are electrostatically confined [5,12,27], and the grain interior (grain boundary free pn junction) where a solution is known. Our approach relies on approximations (or assumptions) which connect these two problems, and render the continuity-Poisson equations along the grain boundary core analytically tractable.…”

Enhanced Photoelectrochemical Water Oxidation from CdTe Photoanodes Annealed with CdCl2

“…Solar cells based on polycrystalline CdTe film photoabsorbers have exhibited higher solar energy conversation efficiencies after a CdCl 2 annealing treatment . The performance parameters of these materials, such as the fill factor, open‐circuit voltage, and short circuit current, when acting as photovoltaic devices were improved.…”

“…Clearly, this photoanodic current was much lower than the photocathodic current obtained from aCdTephotocathode,aswas the maximum photocurrent density.H owever, the polycrystalline CdTef ilm in this prior work contained an umber of grain boundaries that would be expected to trap many photoexcited charge carriers,t hus enhancing recombination and consequently lowering the photoactivity. [36][37][38][39][40][41] Therefore, to enhance the PEC properties of CdTe-based photoanodes,it is essential to decrease the density of grain boundaries in the CdTea bsorber layer.…”

“…Solar cells based on polycrystalline CdTef ilm photoabsorbers have exhibited higher solar energy conversation efficiencies after aC dCl 2 annealing treatment. [36][37][38][39][40][41][42][43][44][45] The performance parameters of these materials,s uch as the fill factor,o pen-circuit voltage,a nd short circuit current, when acting as photovoltaic devices were improved. This improvement occurred because the CdCl 2 annealing facilitated recrystallization of the CdTef ilm, increased the grain size, and extended the lifetime of charge carriers.T he same CdCl 2 treatment also effectively enhanced the activity of CdTebased photocathodes in our recent work.…”