Title: Back-contacted bottom cells with three terminals: Maximizing power extraction from current-mismatched tandem cells

Abstract

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, whilemore » 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.« less

Authors:

Rienäcker, Michael  ^[1];

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Warren, Emily L.  ^[2];

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Schnabel, Manuel ^[2]; Schulte‐Huxel, Henning ^[3]; Niepelt, Raphael ^[4]; Brendel, Rolf ^[1]; Stradins, Pauls ^[2]; Tamboli, Adele C. ^[2]; Peibst, Robby ^[1]

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+ Show Author Affiliations

1. Inst. for Solar Energy Research Hamelin (ISFH), Emmerthal (Germany); Leibniz Univ. Hannover, Hannover (Germany)
2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
3. National Renewable Energy Lab. (NREL), Golden, CO (United States); Inst. for Solar Energy Research Hamelin (ISFH), Emmerthal (Germany)
4. Institute for Solar Energy Research Hamelin (ISFH) Emmerthal Germany

Publication Date:

2019-02-06

Research Org.:

National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office

OSTI Identifier:

1503161

Alternate Identifier(s):

OSTI ID: 1493641

Report Number(s):

NREL/JA-5900-71667
Journal ID: ISSN 1062-7995

Grant/Contract Number:  

AC36-08GO28308; AC36‐08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

Progress in Photovoltaics

Additional Journal Information:

Journal Volume: 27; Journal Issue: 5; Journal ID: ISSN 1062-7995

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY; 36 MATERIALS SCIENCE; 3T; bipolar junction transistor tandem bottom cell; current-mismatch; interdigitated back contact cell (IBC); tandem solar cell; three terminal