Title:	Unified View on the Recombination-Induced Short-Circuit Current Losses in Solar Cells with High-Low Junctions
Author(s):	T. Ohrdes, R. Peibst, N.-P. Harder, P.P. Altermatt, R. Brendel
Keywords:	Short Circuit Current, Back Surface Field, Front Surface Field
Topic:	WAFER-BASED SILICON SOLAR CELLS AND MATERIALS TECHNOLOGY
Subtopic:	Silicon Solar Cell Characterisation and Modelling
Event:	29th European Photovoltaic Solar Energy Conference and Exhibition
Session:	2BV.8.27
Pages:	1194 - 1197
ISBN:	3-936338-34-5
Paper DOI:	10.4229/EUPVSEC20142014-2BV.8.27
Price:	0,00 EUR
Document(s):	paper

Abstract/Summary:

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It is well known that Jsc of back junction back contacted (BJBC) solar cells is reduced when the rear pitch is increased, sometimes called “electrical shading”. It is commonly thought that this happens mainly because the minority carriers suffer from a lower collection efficiency when a larger pitch forces them to travel larger lateral distances in the base. However, we show by means of numerical device simulations that the Jsc losses are mainly caused by increased recombination within the front surface field (FSF) and back surface field (BSF) regions. To understand this effect, one may consider that the recombination in these regions is controlled by the separation of the quasi-Fermi levels EFn,Fp at the base side of the high-low junctions: a larger EFn,Fp at the high-low junction increases the amount of recombination exponentially. In case the base is in low-level injection, EFn,Fp depends on Ndop of the base and therefore recombination in the FSF and BSF is increased at higher Ndop under Jsc conditions (while J0 stays independent of EFn,Fp). Because high-low junctions are also frequently used in other cell structures than BJBC, we develop a unified view that also incorporates back-junction double-side contacted cells (BJDC), common front-junction double-side contacted cells (FJDC), and bifacial cells. We show in general terms that the Jsc losses in any solar cell structure are most pronounced if considerable carrier generation occurs near high-low junctions.