Suppression of hot carriers by nanoporous silicon for improved operation of a solar cell

Abstract

The surface of a silicon solar cell is modified to improve its photovoltaic characteristics. Nanostructured porous silicon layer is formed on a front n+ -type surface of a p–n junction by means of electrochemical etching accompanied by illumination with a high-power light-emitting diode operating at the wavelength of 365 nm. Addition of the porous layer results in considerable increase in the capacitive photovoltage across the p–n junction. This increase is shown to be stipulated by reduced photonic losses due to anti-reflection coating effect of the porous layer, as well as by decreasing adverse effect of hot carriers on the photovoltage. Broadening of the spectrum of capacitive photovoltage towards the short-wavelength region was observed. This finding is associated with the gradedgap character of the porous layer and photovoltage formation across it as well as with increased absorption of high-energy photons in the porous layer and resulting weaker heating of free carriers.