n-Si/SnO2 junctions based on macroporous silicon for photoconversion

For the first time it is demonstrated that a photovoltaic junction can be formed by spraying a thin, transparent, conductive SnO2 layer onto macroporous n-type silicon produced by photoelectrochemical etching. With a macropore density of 107 cm−2, and an average pore diameter in the range 1–2 μm, the cell reflectivity spectrum is flat and drops to a few percent in the visible and near infrared spectral range. EDX analysis and impedance measurements show that charge separation and current collection occur in the upper part of the pores and in the interpore region, whereas the bottom of the pores only acts as a photon absorber. The active junction area is found to be four times larger than with a mirror-polished substrate. A solar cell equipped with just a front ring contact was realized, which attains a solar conversion efficiency of 10% under AM 1.5 conditions.