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An analytical model for the calculation of the band bending in amorphous/crystalline silicon (a-Si:H/c-Si) heterojunctions is presented and validated by comparison with full numerical simulations. The influence of the various structure properties and parameters, such as the density of states in bulk a-Si:H or at interface defects, the position of the Fermi level in a-Si:H, the temperature dependence of band gaps, is investigated. Significant band offsets imply the presence of a strong inverted layer at the c-Si surface of both (p)a-Si:H/(n)c-Si and (n)a-Si:H/(p)c-Si structures, forming two-dimensional hole and electron gases, respectively. This leads to high sheet carrier densities that have been evidenced from planar conductance measurements. Experimental data obtained on samples coming from various research institutes are analyzed with our model in order to extract the band offsets. We find that the valence band offset ranges between 0.32 and 0.42 eV with an average value at 0.36 eV; the conduction band offset is found between 0.08 and 0.26 eV with a mean value at 0.15 eV. These values are discussed in the frame of the branch point theory for band line-up; they imply that the branch point energy in a-Si:H is almost independent of doping and lies close to mid-gap.

The photostability of the amorphous—crystalline silicon heterointerface is investigated. It is revealed that the metastability of hydrogenated amorphous silicon (a-Si:H) causes significant light induced changes in the heterointerface. Unlike bulk a-Si:H, the photostability of the heterointerface is not controlled by the microstructural properties of a-Si:H but rather by the initial heterointerface properties. Interfaces that initially have low interface defect density show the greatest degradation while those that initially have high interface defect density actually show light-induced improvement. It is shown that the degree of light induced change in the interface defect density is linearly proportional to the natural logarithm of the initial interface defect density. Further, it is revealed that the kinetics of light-induced change in the heterointerface defect density can be faster or slower than light-induced changes in bulk a-Si:H films depending on the initial properties of the heterointerface. Light soaking measurements on heterointerfaces with doped a-Si:H films reveal that interface defect density of these structures improves with light soaking. It is proposed that this is caused by a combination of the high initial interface defect density of samples using doped a-Si:H films and reduced generation of defects near the heterointerface due to the enhanced field effect provided by the doped films.

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We present a study of the elastic exciton-electron (X − e − ) and exciton-hole (X − h) scattering processes in semiconductor quantum wells, including fermion exchange effects. The balance between the exciton and the free carrier populations within the electron-hole plasma is discussed in terms of ionization degree in the nondegenerate regime. Assuming a two-dimensional Coulomb potential statically screened by the free carrier gas, we apply the variable phase method to obtain the excitonic wavefunctions, which we use to calculate the 1s exciton-free carrier matrix elements that describe the scattering of excitons into the light cone where they can radiatively recombine. The photon emission rates due to the carrier-assisted exciton recombination in semiconductor quantum-wells (QWs) at room temperature and in a low density regime are obtained from Fermi's golden rule, and studied for mid-gap and wide-gap materials. The quantitative comparison of the direct and exchange terms of the scattering matrix elements shows that fermion exchange is the dominant mechanism of the exciton-carrier scattering process. This is confirmed by our analysis of the rates of photon emission induced by electron-assisted and hole-assisted exciton recombinations.

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The industrial fabrication process of silicon heterojunction (SHJ) solar cells can induce locally depassivated regions (so-called defectivity) because of transportation steps (contact with belts, trays, etc.) or simply the environment (presence of particles at the wafer surfaces before thin film deposition). This surface passivation spatial heterogeneity is gaining interest as it may hinder the SHJ efficiency improvements allowed by incremental process step optimizations. In this paper, an experimentally supported simulation study is conducted to understand how the local a-Si:H/c-Si interface depassivation loss impacts the overall cell performance. The defectivity-induced cell performance drop due to depassivated regions was attributed to a bias-dependent minority carrier current flow towards the depassivated region, which is shown to affect all current-voltage (I(V)) parameters, and in particular the fill factor. Simulation was used further in order to understand how the defectivity properties (spatial distribution, localization and size) impact the induced performance losses. In the light of all results, we propose ways to mitigate the defectivity influence on the cell performances.