Enhanced electrical properties at boundaries including twin boundaries of polycrystalline CdTe thin-film solar cells

Abstract

The effect of grain boundaries (GBs), in particular twin boundaries (TBs), on CdTe polycrystalline thin films is studied by conductive atomic force microscopy (C-AFM), electron-beam-induced current (EBIC), scanning Kelvin probe microscopy (SKPM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). Four types of CdTe grains with various densities of {111} Σ3 twin boundaries (TBs) are found in Cl-treated CdTe polycrystalline thin films: (1) grains having multiple {111} Σ3 TBs with a low angle to the film surface; (2) grains having multiple {111} Σ3 TBs parallel to the film surfaces; (3) small grains on a scale of not more than 500 nm, composed of Cd, Cl, Te, and O; and (4) CdTe grains with not more than two {111} Σ3 TBs. Grain boundaries (including TBs) exhibit enhanced current transport phenomena. However, the {111} Σ3 TB is much more beneficial to micro-current transport. The enhanced current transport can be explained by the lower electron potential at GBs (including TBs) than the grain interiors (GIs). Our results open new opportunities for enhancing solar cell performances by controlling the grain boundaries, and in particular TBs.

Inducing a Nanotwinned Grain Structure within the TiO2 Nanotubes Provides Enhanced Electron Transport and DSSC Efficiencies >10%

“…Beneficial effects of twinned nanostructures on the electronic properties were reported particularly for metallic nanostructures (e.g., Cu nanowires) and for II–VI semiconductor structures (e.g., ZnSe nanowires and ternary chalcogenate (Cd 0.5 Zn 0.5 S) nanorods). The main effects are ascribed to a local increase in mobility or carrier density, as carrier's separation at the boundaries is favored due to the local lateral field between the grain boundaries and grain interiors or alternatively to strain relaxation at twin boundaries . Beneficial effects are also ascribed to the formation of defined homojunctions due to twinning; these junctions were reported to be very efficient in separating photogenerated charges and contributing to prolonged lifetime of both photogenerated electrons and holes …”

Observation of photovoltaic effect within locally doped silicon nanojunctions using conductive probe AFM

“…In particular, in the field of PV, local scale C-AFM investigations (in dark and illuminated conditions) have demonstrated added value in understanding charge transport and in improving the performance of the final device. Numerous C-AFM studies have been carried out on different solar cell configurations (planar, nanowires, cross-section, …) and in particular, on the layers or structures of which they are composed [26][27][28][29][30][31][32]. In this work, the C-AFM method will be used to directly probe the photovoltaic properties of nanojunctions formed in a c-Si wafer.…”

Nanotwin Detection and Domain Polarity Determination via Optical Second Harmonic Generation Polarimetry

“…PFM, typically probing ferroelectric domains, is not applicable to semiconductor nanotwins due to high electrical conductivity of typical semiconductors 22,23 .…”