Monolithic Selenium/Silicon Tandem Solar Cells

Featured in Physics
Open Access

Monolithic Selenium/Silicon Tandem Solar Cells

Rasmus Nielsen, Andrea Crovetto, Alireza Assar, Ole Hansen, Ib Chorkendorff, and Peter C.K. Vesborg

PRX Energy 3, 013013 – Published 12 March 2024

See synopsis: Testing a New Solar Sandwich

Abstract

Selenium is experiencing renewed interest as a promising candidate for the wide bandgap photoabsorber in tandem solar cells. However, despite the potential of selenium-based tandems to surpass the theoretical efficiency limit of single-junction devices, such a device has never been demonstrated. In this study, we present the first monolithically integrated selenium/silicon tandem solar cell. Guided by device simulations, we investigate various carrier-selective contact materials and achieve encouraging results, including an open-circuit voltage of $V_{oc} = 1.68 V$ from suns- $V_{oc}$ measurements. The high open-circuit voltage positions selenium/silicon tandem solar cells as serious contenders to the industrially dominant single-junction technologies. Furthermore, we quantify a pseudo fill factor of more than 80% using injection-level-dependent open-circuit voltage measurements, indicating that a significant fraction of the photovoltaic losses can be attributed to parasitic series resistance. This work provides valuable insights into the key challenges that need to be addressed for realizing higher efficiency selenium/silicon tandem solar cells.

Received 25 October 2023
Revised 1 December 2023
Accepted 2 February 2024

DOI:https://doi.org/10.1103/PRXEnergy.3.013013

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Tandem photovoltaics

Device fabrication Solar cells

Physical vapor deposition

Energy Science & TechnologyCondensed Matter, Materials & Applied Physics

synopsis

Testing a New Solar Sandwich

Published 12 March 2024

By combining the world’s oldest photovoltaic material with today’s most used one, researchers have taken a step toward next-generation solar devices.

See more in Physics

Authors & Affiliations

Rasmus Nielsen ^1,*, Andrea Crovetto ², Alireza Assar ², Ole Hansen ², Ib Chorkendorff ¹, and Peter C.K. Vesborg ¹

¹SurfCat, DTU Physics, Technical University of Denmark, Kongens Lyngby 2800, Denmark
²National Center for Nano Fabrication and Characterization (DTU Nanolab), Technical University of Denmark, Kongens Lyngby 2800, Denmark

^*raniel@dtu.dk

Popular Summary

Increasing the efficiencies of solar cells is a powerful lever for cost reduction of photovoltaic (PV) systems. However, the efficiencies of single-junction PV technologies have nearly reached their practical limits. Tandem solar cells, which integrate two absorbers with different bandgaps into a single device, hold promise for achieving significantly higher device efficiencies; nevertheless, only a few such devices have reached commercialization. The main challenge for realizing the next-generation, low-cost tandem solar cell is the identification of a wide-bandgap top cell that is process compatible with a low-bandgap bottom cell while maintaining high performance, low cost and long-term stability. In this work, the authors present a monolithically integrated selenium/silicon tandem solar cell. Combining experiment and device simulation, the device architecture and heterostructure interfaces are investigated, providing valuable insight into the key challenges that must be addressed to realize higher efficiencies.

Key Image

Article Text

Click to Expand

Supplemental Material

Click to Expand

References

Click to Expand

Issue

Vol. 3, Iss. 1 — March - May 2024

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Device architecture of the three-terminal monolithic selenium/silicon tandem solar cell. (a) Schematic illustration of the device structure using either $Zn Mg O$ or ${Ti O}_{2}$ as the $n$ -type contact. (b) Cross-section SEM image of the tandem solar cell. Photographs of the device are also shown.
Reuse & Permissions
Figure 2
Photovoltaic device performance of the $Zn Mg O$ -based selenium/silicon tandem and parallel-processed bifacial selenium single junction solar cells. (A) Current-voltage (J-V) curves measured under 1-sun and dark conditions, accompanied by the J-V curve reconstructed from suns- $V_{oc}$ measurements. (B) Equivalent J-V characterization for the bifacial single junction, with the device illuminated through either the hole- or electron transport layer (HTL or ETL). (C) External quantum efficiency (EQE) spectra of each subcell measured under short-circuit conditions, along with the spectra of the selenium top cell under reverse bias conditions. The AM1.5G-equivalent short-circuit current density of each subcell has been integrated and highlighted in bold. (D) EQE spectra of the bifacial single junction illuminated through either the HTL or ETL under short-circuit and reverse applied biases.
Reuse & Permissions
Figure 3
Characterization of energy-band positions and simulated device performance. (a) Ultraviolet photoemission spectroscopy (UPS) measurements of $Zn Mg O$ , ${Ti O}_{2}$ , and poly- $Se$ thin films. The valence band offsets relative to the Fermi level are extrapolated from the leading edges of the spectra, and the work functions are calculated from the secondary electron cutoffs. A small bias of $- 5 V$ is applied to the samples to deconvolute the work function of the surface from that of the analyzer, and a gold leaf is mounted in electrical contact with each sample to accurately determine the Fermi level. (b) Tauc plots derived from UV-vis transmission measurements. The optical bandgap of each thin film is linearly extrapolated from the absorption onsets. (c) Simulated energy-band diagrams of the poly- $Se$ /ETL/TCO heterostructure under open-circuit conditions, featuring an arbitrary TCO with a work function of $WF = 4.4 eV$ . (d) Simulated J-V curve sensitivity of the $Zn Mg O$ -based single-junction device as the TCO work function is varied from 4.1 to 4.8 eV. (e) The equivalent sensitivity analysis of the ${Ti O}_{2}$ -based single-junction device.
Reuse & Permissions
Figure 4
Photovoltaic device performance of the ${Ti O}_{2}$ -based selenium/silicon tandem solar cell. (a) Current-voltage (J-V) curves measured under 1 Sun and dark conditions. (b) External quantum efficiency (EQE) spectra of each subcell measured under short-circuit conditions, along with the spectra of the selenium top cell under reverse-bias conditions. The AM1.5G-equivalent short-circuit current density of each subcell has been integrated and highlighted in bold. (C) J-V curve reconstructed from suns- $V_{oc}$ measurements, where the effects of series resistance have been eliminated. (d) Batch statistics of the performance metrics of the ${Ti O}_{2}$ -based tandem devices compared to the $Zn Mg O$ -based tandem device.
Reuse & Permissions

PRX Energy