TY - JOUR

T1 - Back-contacted bottom cells with three terminals

T2 - Maximizing power extraction from current-mismatched tandem cells

AU - Rienäcker, Michael

AU - Warren, Emily L.

AU - Schnabel, Manuel

AU - Schulte-Huxel, Henning

AU - Niepelt, Raphael

AU - Brendel, Rolf

AU - Stradins, Paul

AU - Tamboli, Adele C.

AU - Peibst, Robby

N1 - Funding information: The funding for this work was provided by the German State of Lower Saxony, the German Federal Ministry for Economics and Energy (BMWi) within the research project “EASi” (FKZ0324040), and the European Union's Seventh Program for research, technological development, and demonstration within the project “HERCULES” under grant agreement no. 608498. This work was authored in part by the Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the US Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the US Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a nonexclusive, paid up, irrevocable, and worldwide license to publish or reproduce the published form of this work, or allow others to do so, for US Government purposes. H. Schulte-Huxel acknowledges support for the Research Fellowship by Deutsche Forschungsgemeinschaft (DFG) (grant agreement No: SCHU 3206/1-1). The authors wish to thank H. Kohlenberg, T. Friedrich, M. Tatarzyn, S. Schmidt, A. Raugewitz, R. Winter, N. Wehmeier, F. Heinemeyer, J. Hensen, D. Sylla, T. Neubert for sample processing at ISFH. We appreciate G. Glowatzki, B. Koch and J. Krügener form Institute of Electronic Materials and Devices (MBE) at Leibniz Universität Hannover for helping with LPCVD deposition and ion implantation. The authors would like to thank M. Pickrell from Sun Chemical Ltd. for providing hotmelt wax.

PY - 2019/4/2

Y1 - 2019/4/2

N2 - Multi-junction cells can significantly improve the energy yield of photovoltaic systems over a single-junction cell. The internal interconnection scheme of the subcells is an important aspect in determining the resulting levelized cost of electricity. For a dual-junction cell, two approaches are commonly discussed: series-connected tandem cells with two terminals or independently working subcells in a four-terminal (4T) tandem device. In this paper, we explore the working principle and the operation modes of a third, rarely discussed option: a three-terminal (3T) tandem cell using a back-contacted bottom cell with 3Ts. We use current–voltage measurements of illuminated 3T interdigitated back contact cells and confirm that the front and rear base contacts are at similar quasi-Fermi level positions, which enables the bottom cell to either efficiently collect surplus carriers, in the case of a current-limiting or carrier injecting top cell, or inject majority carriers, in the case of a current-limiting bottom cell. As a result, no current matching is needed. The power output of an idealized 3T bottom cell without resistive effects is independent of the current density applied from the top cell. These characteristics of the 3T bottom cells enable a 3T tandem to operate as efficiently as a 4T tandem, while being compatible with monolithic design and not requiring intermediate grids. We propose a simple equivalent circuit model including additional resistive effects, which describes a real 3T bottom cell and achieves excellent agreement to the experiment. We deduce design guidelines for a 3T bottom cell in different operation regimes.

AB - Multi-junction cells can significantly improve the energy yield of photovoltaic systems over a single-junction cell. The internal interconnection scheme of the subcells is an important aspect in determining the resulting levelized cost of electricity. For a dual-junction cell, two approaches are commonly discussed: series-connected tandem cells with two terminals or independently working subcells in a four-terminal (4T) tandem device. In this paper, we explore the working principle and the operation modes of a third, rarely discussed option: a three-terminal (3T) tandem cell using a back-contacted bottom cell with 3Ts. We use current–voltage measurements of illuminated 3T interdigitated back contact cells and confirm that the front and rear base contacts are at similar quasi-Fermi level positions, which enables the bottom cell to either efficiently collect surplus carriers, in the case of a current-limiting or carrier injecting top cell, or inject majority carriers, in the case of a current-limiting bottom cell. As a result, no current matching is needed. The power output of an idealized 3T bottom cell without resistive effects is independent of the current density applied from the top cell. These characteristics of the 3T bottom cells enable a 3T tandem to operate as efficiently as a 4T tandem, while being compatible with monolithic design and not requiring intermediate grids. We propose a simple equivalent circuit model including additional resistive effects, which describes a real 3T bottom cell and achieves excellent agreement to the experiment. We deduce design guidelines for a 3T bottom cell in different operation regimes.

KW - 3T

KW - bipolar junction transistor tandem

KW - bottom cell

KW - current-mismatch

KW - interdigitated back contact cell (IBC)

KW - tandem solar cell

KW - three terminal

UR - http://www.scopus.com/inward/record.url?scp=85061306039&partnerID=8YFLogxK

U2 - 10.1002/pip.3107

DO - 10.1002/pip.3107

M3 - Article

AN - SCOPUS:85061306039

VL - 27

SP - 410

EP - 423

JO - Progress in Photovoltaics: Research and Applications

JF - Progress in Photovoltaics: Research and Applications

SN - 1062-7995

IS - 5

ER -