Stresses and their relation to defects in multicrystalline solar silicon

Abstract

We report research on the characterization of stresses in relation to defects in multicrystalline silicon (mc-Si) solar cell material. Photoelasticity and micro-Raman spectroscopy (µRS) techniques are combined to understand this correlation at different length scales. While photoelasticity can probe small residual thermal stresses distributed over the entire volume of the sample as well as local stresses caused by defects, RS can measure very localized intrinsic stresses of defects existing at the sample surface. Defects such as dislocations and inclusions are usually accompanied by stresses. In combination with thermal stresses, it results in a global residual stress state in the material. Thermal stresses are induced by the mismatch of different coefficients of thermal expansion between inclusions and silicon as well as due to local inhomogeneous temperature gradients during crystallization. Thermal stresses that relax by forming efficiency limiting defects can be redu ced below the yield stress values by optimizing the crystallization conditions using photoelasticity

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

“…For the cubic Co 3 O 4 microcrystals (>12 h), increasing the thermal‐treatment time has an effect on the decreasing bandgap . In these three morphologies: hedgehog sphere‐like, lamellar and cubic, the cubic Co 3 O 4 grains have the largest bandgap energy according to our test data, the reasons for this need more experiments for verification.…”

“…The full width at half‐maximum (FWHM) of the Raman peak displays the distribution and qualitative comparison of defect density . Figure b shows the FWHM of Raman modes for as‐prepared Co 3 O 4 microparticles.…”

Optical Emission Spectroscopy Studies in ECR Plasma Used for the Deposition of Silicon Oxide Film

“…It could be proved that SiH*/Ar* was regarded as a basis for judging deposition rate by the same trend. From the peak and FWHM of Raman spectrum in Fig.5 (d), it could be seen that when H 2 /SiH 4 increase from 0.2 to 1, the thin films are amorphous phase and with more defects from stress (12)(13).…”

Future of raman in PV development

“…3 (f). The crystal defects in the as-grown silicon thin films result from the partial or total relaxation of thermal stresses as long as the plastic deformation is allowed by temperature and the thermal stress level is above the yield value [17]. The thermal stresses are mainly produced by (1) inhomogeneous temperature gradients during melting and re-crystallization of the amorphous silicon seed layer, (2) the difference in the coefficients of thermal expansion (CTE) between the crystalline silicon film and the borosilicate glass (BSG) substrate as well as the silicon oxide film at the surface, and (3) the grain orientation (microstructure) dependent elastic and plastic deformation.…”