Despite the impressive performance and incredible promise for a variety of applications, the wide-scale commercialization of graphene is still behind its full potential. One of the main challenges is related to preserving graphene’s unique properties upon transfer onto practically desirable substrates. In this work, few-layer graphene sheets deposited via liquid-phase transfer from copper onto a quartz substrate have been studied using a suite of experimental techniques, including scanning electron microscopy (SEM), Raman spectroscopy, admittance spectroscopy, and four-point probe electrical measurements. SEM measurements suggest that the transfer of graphene from copper foil to quartz using the aqueous solution of ammonium persulfate was accompanied by unintentional etching of the entire surface of the quartz substrate and, as a result, the formation of microscopic facet structures covering the etched surface of the substrate. As revealed by Raman spectroscopy and the electrical measurements, the transfer process involving the etching of the copper foil in a 0.1 M solution of (NH4)2S2O8 resulted in its p-type doping. This was accompanied by the appearance of an electronic gap of 0.022 eV, as evidenced by the Arrhenius analysis. The observed increase in the conductance of the samples with temperature can be explained by thermally activated carrier transport, dominating the scattering processes.

Introduction. Heterojunction silicon solar cells represent one of the most promising directions for the development of solar photovoltaics. This is due to both their high power conversion efficiency and reasonable likelihood for further growth in performance, as well as good commercial potential of this technology, which relies on a transition from conventional diffusion-based processes to thin film deposition. Aim. The paper describes results of optimization and fabrication of heterojunction silicon solar cells using the AK-1000 inline tool, adapted for processing of 6-inch wafers. Materials and methods. In the manufacturing of solar cells, crystalline silicon wafers were subjected to wet chemical processes, and then electron, hole, and intrinsic types of conductivity of the layers based on amorphous silicon were deposited by plasma-chemical deposition. Precipitation of oxide transparent conductive layers was carried out by magnetron sputtering. To optimize the processes of obtaining solar cells, measurements of the reflection coefficient, of lifetime of minority carriers, and of current-voltage characteristics were used. Results. As a result of the work, heterojunction solar cells were obtained in a laboratory in Kazakhstan with an efficiency of 20% without using of traditional diffusion processes for solar cells manufacturing. Conclusions. The output parameters associated with light conversion efficiency demonstrate the possibility of further optimization of the parameters affecting the performance of heterojunction solar cells.

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