An anomalous increase in the fill factor of the current-voltage characteristic in the short-wave region of the solar spectrum for a silicon photocell containing a porous-silicon structure

The possibility of increasing the efficiency of a silicon photocell by forming a porous-silicon structure in its bulk has been proposed and studied. Photocells produced from $p$-type single-crystal silicon plates by the diffusion method were investigated. Porous-silicon structures were formed by photoelectric anodic etching in HF-ethanol mixture. Current density and etching time were assigned by a computer in ranges of 6–14 mA/cm$^2$ and 10–20 s, respectively. It has been found that the porous-silicon structure located in the emitter bulk substantially improves efficiency of photocells. At wavelength $\lambda\sim$ 550 nm, an anomalously large (by five to nine times) increase in efficiency was observed.