Novel chemical cleaning of textured crystalline silicon for realizing surface recombination velocity

Abstract

In this study, the development of a novel chemical cleaning method suitable for textured surfaces of crystalline silicon (c-Si) used for solar cells is demonstrated. To remove contaminants from such textured structures, chemicals have to penetrate into their complicated fine structures. Thus, the viscosity, reaction activity, and surface tension of the chemicals are adjusted by increasing the reaction temperature or introducing a surfactant. Actually, the use of concentrated (conc.) sulfuric acid (H2SO4) of 140 °C and the introduction of methanol (CH3OH) to other chemicals contribute to the improvement of the cleaning ability in textured structures. The present cleaning method in conjunction with plasma-damage-less catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD passivation with silicon–nitride (SiNx)/amorphous silicon (a-Si) stacked layers, also contributes to the decrease in the surface recombination velocity (SRV) of c-Si. The maximum estimated SRV (SRVmax), evaluated under the assumed absence of recombination in bulk c-Si, is less than 1.1 cm/s for textured surfaces, and the real SRV, evaluated by changing the c-Si substrate thickness, is less than 0.2 cm/s.