Highly efficient radial-junction microwire solar cells by acid based doping process

Abstract

We propose a novel doping method to fabricate highly efficient radial-junction microwire solar cells using acid solutions (boric and phosphoric acids). Compared to the conventionally used toxic gas (POCl3 and BBr3) or polymer based (spin-on-dopant) doping sources, acid doping processes intrinsically have outstanding advantages such as high purity, non-toxic, and low cost process. High quality junctions for both emitter and back-surface-field (BSF) were successfully formed in the microwire solar cells using the acid doping processes. The measured minority carrier life time of microwire solar cells after the acid doping processes showed approximately three times higher value (66 us) compared to that after polymer based spin-on-doping process (23 us). Consequently, our best device with areas of 1 cm2 exhibited power conversion efficiencies (Eff) of up to 20% under AM 1.5G illumination. In particularly, the acid doping based solar cells showed notable increase (40 mV) in the open-circuit voltage (Voc) of 630 mV compared to that of spin-on-doping based solar cells (590 mV) due to the high purity of acid doping sources. This corresponds to an approximately 11.6 % increase in the Eff compared to that of spin-on-doping based solar cell (Eff = 18 %). Hence, we believe that the proposed acid doping processes would become a foundational technology for the development of highly efficient and cost-effective radial-junction solar cells.