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Analysis and minimisation of resistive losses in high-efficiency Si solar cells by combining measurements with numerical modelling(1995) Altermatt, Peter; Heiser, Gernot; Zhao, Jun; Wang, Alan; Wenham, Stuart; Green, MartinConference Paper
(1996) Altermatt, Peter; Heiser, Gernot; Aberle, Armin; Wang, Alan; Zhao, Jun; Robinson, J; Bowden, Simon; Green, MartinJournal ArticleThis paper presents an improved method for measuring the total lumped series resistance (Rs) of high-efficiency solar cells. Since this method greatly minimizes the influence of non-linear recombination processes on the measured Rs values, it is possible to determine Rs as a function of external current density over a wide range of illumination levels with a significantly improved level of accuracy. This paper furthermore explains how resistive losses in the emitter, the base, the metal/silicon contacts and the front metal grid can be separately determined by combining measurements and multidimensional numerical simulations. A novel combination of device simulation and circuit simulation is introduced in order to simulate complete 2 × 2 cm2 PERL (passivated emitter and rear locally-diffused) silicon solar cells. These computer simulations provide improved insight into the dynamics of resistive losses, and thus allow new strategies for the optimization of resistive losses to be developed. The predictions have been experimentally verified with PERL cells, whose resistive losses were reduced to approximately half of their previous values, contributing to a new efficiency world record (24.0%) for silicon solar cells under terrestrial illumination. The measurement techniques and optimization strategies presented here can be applied to most other types of solar cells, and to materials other than silicon.
(1995) Aberle, Armin; Altermatt, Peter; Heiser, Gernot; Robinson, Steven J.; Wang, Alan; Zhao, Jun; Krumbein, U; Green, MartinJournal ArticleThe `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