Modeling of two-junction, series-connected tandem solar cells using top-cell thickness as an adjustable parameter

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Abstract
Theoretical efficiencies are calculated for two‐junction, series‐connected solar cells using air mass 1.5 global and direct irradiancespectra. For band‐gap combinations previously limited by a low bottom‐cell current, thinning of the top cell is shown to result in significant increases in the theoretical efficiencies. The increases are primarily due to increased short‐circuit currents, since current matching is achievable. Smaller gains are also seen in the open‐circuit voltages of the thinner cells when a low surface‐recombination velocity is assumed. Thus, a number of material combinations which previously could only be used in four‐terminal configurations can now be considered for series‐connected two‐junction solar cells.