Multijunction devices consist of a stack of semiconductor junctions having bandgaps tuned across a broad spectrum. In solar cells this concept is used to increase the efficiency of photovoltaic harvesting, while light emitters and detectors use it to achieve multicolor and spectrally tunable behavior. In series-connected current-matched multijunction devices, the recombination layers must allow the hole current from one cell to recombine, with high efficiency and low voltage loss, with the electron current from the next cell. We recently reported a tandem solar cell in which the recombination layer was implemented using a progression of n-type oxides whose doping densities and work functions serve to connect, with negligible resistive loss at solar current densities, the constituent cells. Here we present the generalized conditions for design of efficient graded recombination layer solar devices. We report the number of interlayers and the requirements on work function and doping of each interlayer, to bridge an work function difference as high as 1.6 eV. We also find solutions that minimize the doping required of the interlayers in order to minimize optical absorption due to free carriers in the graded recombination layer (GRL). We demonstrate a family of new GRL designs experimentally and highlight the benefits of the progression of dopings and work functions in the interlayers. © 2012 American Chemical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-11-009-21
Acknowledgements: This publication is based in part on work supported by an award (no. KUS-11-009-21) made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, by the Natural Sciences and Engineering Research Council (NSERC) of Canada, and by Angstrom Engineering and Innovative Technology. The authors would also like to acknowledge the assistance of Larissa Levina, Armin Fisher, Elenita Palmiano, Remigiusz Wolowiec, and Damir Kopilovic. G.I.K. acknowledges NSERC support in the form of Alexander Graham Bell Canada Graduate Scholarship. X.W. was partially supported by an Ontario Post Doctoral Fellowship from the Ontario Ministry of Research and Innovation.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.