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

Abstract

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