Surface composition and depth profile studies of chemiplated thin film CdS:Cu2S solar cells have been carried out using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. These studies indicate that the junction is fairly diffused in the as-prepared cell. However, heat treatment of the cell at 210 degrees C in air relatively sharpens the junction and improves the cell performance. Using the Cu(2p32/)/S(2p) ratio as well as the Cu(LVV)/(LMM) Auger intensity ratio, it can be inferred that the nominal valency of copper in the layers above the junction is Cu+ and it is essentially in the Cu2S form. Copper signals are observed from layers deep down in the cell. These seem to appear mostly from the grain boundary region. From the observed concentration of Cd, Cu and S in these deeper layers and the Cu(LVV)/(LMM) ratio it appears that the signals from copper essentially originate partly from copper in CuS and partly from Cu2+ trapped in the lattice. It is significant to note that the nominal valence state of copper changes rather abruptly from Cu+ to Cu2+ across the junction.

This work presents an experimental and finite difference time domain (FDTD) simulation-based study on the application of graphene as a transparent conducting layer on a planar and untextured crystalline p-n silicon solar cell. A high-quality monolayer graphene with 97% transparency and 350 Ω/□ sheet resistance grown by atmospheric pressure chemical vapor deposition method was transferred onto planar Si cells. An increase in efficiency from 5.38% to 7.85% was observed upon deposition of graphene onto Si cells, which further increases to 8.94% upon SiO2 deposition onto the graphene/Si structure. A large increase in photon conversion efficiency as a result of graphene deposition shows that the electronic interaction and the presence of an electric field at the graphene/Si interface together play an important role in this improvement and additionally lead to a reduction in series resistance due to the conducting nature of graphene.

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To counter the problem of instability, irreproducibility, and low stoichiometry of p-CuxS layers in thin-film CdS solar cells, a new field-assisted chemiplating process of barrier formation is described. Using the dc-forming potential as a first-order variable, nominal deviation from Cu2S composition without any dependence on external process parameters has been obtained. The stability of higher composition CuxS is attributed to the formation of a Cd++, rich barrier layer at the growing CuxS interface towards the CdS side, as inferred from the spectral response and Auger Cu and Cd compositional depth profile of the solar cells.

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