Conversion efficiency in silicon solar cells with spatially non-uniform doping.pdf

32 ? 1999, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine Semiconductor Physics, Quantum Electronics Optoelectronics. 1999. V. 2, N 3. P. 32-37. Pacs: 84.60.J; 72.20.J Conversion efficiency in silicon solar cells with spatially non-uniform doping A.V. Sachenko, N.A. Prima, A.P. Gorban Institute of Semiconductor Physics, NAS of Ukraine 45, prospect Nauki, 252650 Kyiv, Ukraine Abstract. The conversion efficiency of diffusion-type silicon solar cells, η, is studied theoretically in assumption of different doping levels existing under collection grid contacts and within the inter-contact spacing. It is shown that at high under-contact doping levels and at relatively low inter-contact doping ones the conversion efficiency increases as compared to uniform doping case. The dependence of η on Shockley-Reed-Hall carrier lifetimes both in the base and in the top-surface n + -layer as well as on the depth of p-n-junction and the shape of electron concentration profile, N(x), in the n + -region is analysed. Keywords: silicon solar cell, p-n-junction, conversion efficiency. Paper received 02.07.99; revised manuscript received 25.10.99; accepted for publication 26.10.99. 1. Introduction As shown in papers [1-3], extremely high values of conver- sion efficiency in diffusion-type n + -p-p + silicon solar cells (SC) can be achieved only at high doping levels of n + - and p + -regions and at small thickness of top-surface n + -layer ( ≤ 10 -5 cm -3 ). That is caused by the necessity of minimiza- tion of SC internal resistance, effective surface recombina- tion rates under top and rear surface contacts and recombina- tion losses resulting from bulk recombination in the highly doped n + - region. Important part of energy losses in SC is caused by short-circuit current reduction due to recombina- tion of minority carriers and due to absorption of photo- active part of sun-light flux by free charge carriers within highly doped n + - and p + - regions. Be