Limiting loss mechanisms in 23% efficient silicon solar cells

Abstract

The `passivated emitter and rear locally diffused` (PERL) silicon solar cell structure presently demonstrates teh highes terrestrial performance of any silicon-based solar cell. This paper presents a detailed investigation of the limiting loss mechanisms in PERL cells exhibiting independently confirmend 1-sun efficiencies of up to 23.0%. Optical, resistice, and recombinative losses are all analyzed under the full range of solar cell operating conditions with the aid of two-dimensional (2D) device simulations. The analysis is based on measurements of the reflectance, quaantum efficiency, dark and illuminated current-voltage (I-V) characteristics, and properties of the Si-SiO2 interfaces employed on these cells for surface passivation. Through the use of the 2D simulations, particular attention has been paid to the magnitudes of the spatially resolved recombination losses in these cells. Itis shown that approximately 50% of the recombination losses at the 1-sun maximum power point occur in the base of th cells, followed by the recombination losses at the rear and front oxidised surfaces (25% and <25%, respectively). The relativerly low fill factors of PERL cells are princip[ally a result of resistive losses; however, the recombination behavior in the base and at the rear surfacealso contributes. This work predicts that the efficiency of 23% PERL cells could be increased by about 0.7% absolute if ohmic losses were eliminated, a further 1.1% absolute if there were no reflection losses at the nonmetallised front surface regions, about 2.0% by introducing ideal light trapping and eliminating shading losses due to the front metallisation, and by about 3.7% absolute if the device had no defect-related reconbination losses. New design rules for future efficiency improvements, ev