ARTICLE IN PRESS
Solar Energy Materials & Solar Cells 90 (2006) 2952–2959
0927-0248/$ -
doi:10.1016/j
Correspo
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Efficiency limits for single-junction and tandem
solar cells
F. Meillaud, A. Shah, C. Droz, E. Vallat-Sauvain, C. Miazza
Institute of Microtechnology (IMT), University of Neuchâtel, A.-L Breguet 2, 2000 Neuchâtel, Switzerland
Received 24 May 2005; accepted 21 September 2005
Available online 28 August 2006
Abstract
Basic limitations of single-junction and tandem p– n and p– i– n diodes are established from
thermodynamical considerations on radiative recombination and semi-empirical considerations on
the classical diode equations. These limits are compared to actual values of short-circuit current,
open-circuit voltage, fill factor and efficiency for amorphous (a-Si:H) and microcrystalline (mc-Si:H)
silicon solar cells. For single-junction cells, major efficiency gains should be achievable by increasing
the short-circuit current density by better light trapping. The limitations of p– i– n junctions are
estimated from recombination effects in the intrinsic layer. The efficiency of double-junction cells is
presented as a function of the energy gap of top and bottom cells, confirming the ‘micromorph’
tandem (a-Si:H/mc-Si:H) as an optimum combination of tandem solar cells.
r 2006 Elsevier B.V. All rights reserved.
Keywords: Amorphous and microcrystalline silicon; Single p–n and p– i–n junction solar cells; Tandem solar cells;
Efficiency limits
1. Introduction
Thin-film silicon solar cells are regularly presented as a one of the main future options
for cost-effective solar cells [1–3]. But, parallel to a price reduction, it is imperative to
improve the efficiency of current solar cells. It is therefore useful to look in detail at the
existing efficiency limitations, introducing estimated values for the dark current in the
see front matter r 2006 Elsevier B.V. All rights reserved.
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