0.76% absolute efficiency increase for screen-printed multicrystalline silicon solar cells with nanostructures by reactive ion etching

In this study, the reactive ion etching in combination with alkaline etching was employed to texture the surface of a 156×156 mm² multi-crystalline silicon wafers to reduce their solar reflectivity and improve conversion efficiency. Reactive gases comprising chlorine (Cl₂), sulfur hexafluoride (SF₆) and oxygen (O₂), were activated in the radio-frequency (rf) plasma to fabricate pyramids in an reactive ion etching (RIE) system. The multi-crystalline Si substrates were etched in various compositions of gases to form the nanostructures of various shapes. Besides the nanoscale features, the high density of nanostructures formed on the multi-crystalline Si surface was also required to significantly reduce the reflectivity. A low reflectivity surface was successfully fabricated with the average reflectivity significantly reduced down to <2% for the wavelength range of 300-850 nm. The short wavelength spectral response (blue response) improvement is observed in RIE textured solar cells compared to the standard textured cells. The RIE textured surfaces in combination with optimized emitter resistance result in a remarkable enhancement of short circuit current density. Compared with the acidic textured solar cells, the absolute conversion efficiency of the alkaline+RIE textured cells was improved by 0.76% in average.