Detailed balance analysis of area de-coupled double tandem photovoltaic modules
Original version
Strandberg, R. (2015). Detailed balance analysis of area de-coupled double tandem photovoltaic modules. Applied Physics Letters, 106(3). doi: 10.1063/1.4906602Abstract
This paper describes how layers of area de-coupled top and bottom cells in photovoltaic tandem
modules can increase the efficiency of two-terminal tandem devices. The point of the area
de-coupling is to allow the number of top cells to differ from the number of bottom cells. Within
each of the layers, the cells can be horizontally series-connected and the layers can then be currentor
voltage-matched with each other in a tandem module. Using detailed balance modeling, it is
shown that two-terminal tandem modules of this type can achieve the same theoretical efficiency
as stacks of independently operated cells, often referred to as four-terminal cells. Optimal ratios of
the number of bottom cells to the number of top cells are calculated. Finally, it is shown that
modules with a bottom layer consisting of 60 cells with a band gap of 1.11 eV, resembling standard
silicon modules, offer sufficient resolution to optimize the number of top cells and achieve
high efficiency over a large range of top cell band gaps. This result extends the list of materials
that can be used as top cells in two-terminal tandem modules with silicon bottom cells.
Description
Published version of an article in the journal: Applied Physics Letters. Also available from the publisher at: http://dx.doi.org/10.1063/1.4906602