Study on the cleaning process of n+-poly-Si wraparound removal of TOPCon solar cells

Abstract

The use of tunnel oxide passivated contact (TOPCon) solar cells on the n-type Cz-Si wafers has thus far attracted more interest in the photovoltaics (PV) industry. However, the cells encounter the problems of wraparound appearance and edge leakage current. These phenomena can result in the decrease in the optical and electrical performance of the cells, such as open circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF). In this work, several cleaning processes were adopted to resolve the problems for cells. The wraparound model and experimental results indicated that an effective cleaning process was carried out and revealed the correlation between the removal of the wraparound film and the edge junction layer on the surface of wafers. The optimized cleaning process did not destroy the boron-doping layer on the front side, and the poly-Si layer on the rear side. This process combined an inline etching process of HF/HNO3 treatment and a batch-type etching process of the KOH/polish additives solution treatment, which could effectively solve the problems associated with optical properties and achieve a low reversed-biased junction leakage current (IRev) 0.15 A at −14.5 V. After optimization of the rear surface recombination and the boron diffusion processes, industrial-type TOPCon cells at the present pilot line were obtained with the efficiency (Eff), Voc, Jsc and FF of 23.53%, 706 mV, 40.65 mA/cm2 and 82.02%, respectively. This optimized cleaning process could be applied and promoted in the PV industry.