Fluorine- and tin-doped indium oxide films grown by ultrasonic spray pyrolysis: Characterization and application in bifacial silicon concentrator solar cells

Abstract

Multi-wire metallization and interconnection for silicon solar cells is considered as a revolutionary technology for the next generation of photovoltaic modules, since it drastically reduces their cost while boosting efficiency. In this paper, we report results obtained using an innovative approach for the fabrication of bifacial low-concentrator Ag-free Cz-Si (Czochralski silicon) solar cells based on an indium fluorine oxide (IFO)/(n+pp+)Cz-Si/indium tin oxide (ITO) structure. Transparent conducting oxide (TCO) layers, IFO and ITO, acting as antireflection electrodes, were grown by ultrasonic spray pyrolysis (USP). A copper wire contact pattern was attached by low-temperature lamination simultaneously to the front and rear TCO layers as well as to the interconnecting ribbons located outside the structure (laminated grid cell (LGCell) design). In this paper, to extend the operating range of sunlight concentration ratios of LGCells, the sheet resistance of the IFO and ITO layers has been reduced to 14 and 13Ω/sq, respectively, by increasing their thickness by about three times, from ∼85 to ∼240 nm. As a result, the operating range of the LGCells has been extended to 1–7suns. In the operating range, their front-illumination efficiency varies from 18.3 to 18.9% (back-illumination efficiency from 15.1 to 15.6%). We also report for the first time the results of systematic analysis of USP IFO properties and compare them with the USP ITO properties. The effect of the IFO thickness on grain size, electrical resistivity, charge carrier concentration and mobility, refractive index, transmission and absorption spectra, as well as optical band gap has been analyzed systematically by scanning electron microscopy, transmission and reflection spectra, optical ellipsometry and Hall measurements.