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Novel Semi-Monolithic Tandem Device Architecture for Photovoltaic and Photoelectrochemical Devices.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Novel Semi-Monolithic Tandem Device Architecture for Photovoltaic and Photoelectrochemical Devices./
Author:	Outlaw-Spruell, Kai.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	63 p.
Notes:	Source: Masters Abstracts International, Volume: 83-03.
Contained By:	Masters Abstracts International83-03.
Subject:	Engineering. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28496327
ISBN:	9798535533407

Novel Semi-Monolithic Tandem Device Architecture for Photovoltaic and Photoelectrochemical Devices.
Outlaw-Spruell, Kai.

Novel Semi-Monolithic Tandem Device Architecture for Photovoltaic and Photoelectrochemical Devices. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 63 p.

Source: Masters Abstracts International, Volume: 83-03.

Thesis (M.S.)--University of Hawai'i at Manoa, 2021.

This item must not be sold to any third party vendors.

Although silicon wafer based solar cells are dominant players in the market, with advanced technologies for large scale production, thin film technologies are studied for their potential in cost-reduction, higher efficiency, light weight, and flexible applications. Among the thin film technologies are the chalcopyrite based thin films, also known as Cu(In,Ga)Se based thin films.While single-junction Cu(In,Ga)Se efficiencies are nearing the performance of polycrystalline silicon, the solar irradiance wavelength range available for use to a single-junction solar cell is limited by the band gap energy of its absorber layer, resulting in inherent conversion efficiency limitations. To utilize a wider range of the solar spectrum, a tandem device utilizing multiple stacked solar cells of varying band gap energies is required. In addition to a wider spectrum absorption, a multi-junction device sums the open circuit voltage of each of the integrated sub-cells, allowing potential for photoelectrochemical water splitting for hydrogen production where voltages in excess of 1.5V are required. The produced hydrogen may be stored and used when sunlight is unavailable.Manufacturing single-junction Cu(In,Ga)Se typically involves layered deposition of elements onto a substrate such as molybdenum coated soda lime glass using vacuum vapor deposition. The p-type absorber Cu(In,Ga)Se requires high temperature for fabrication and annealing, while the n-type buffer layer required to make the p-n junction diode is produced at near room temperature. Because the high temperature annealing required to coarse grains size and fully form the absorber layer will melt the buffer layer and degrade its performance, or render the device inoperable, the manufacturing process is fabricated in the order of p-type absorber and n-type buffer for a single-junction device. During manufacturing tandem devices, the sequence of processing must ensure that the following steps will not destroy the underlying structure, as well as ensuring material compatibility between the top and bottom solar cells for optimal spectral absorption. This places limitations on the types of materials used for tandem devices and its manufacturing processes, leading to reduced performances. Traditional tandem device manufacturing, including monolithic and mechanical integration, lacks technological solutions to thoroughly overcome limitations in material selection and processing when applied to the chalcopyrite class.The proposed solution, the semi-monolithic tandem device architecture, is a novel lift-off and transfer method that allows for fabrication of single junction solar cells, as they are optimized, for subsequent integration with a separately processed cell. This method, once proven, could offer more freedom in material selection for tandem integration, and an easy adaptation of tandem devices to new single junction solar cell advancements.Because Cu(In,Ga)Se cells have unique material properties that facilitates the semi-monolithic manufacturing process, meet top and bottom cell requirements, as well as having one of the highest reported thin film solar cell conversion efficiency, this research focused on Cu(In,Ga)Se solar cells. A CuGa3Se5 (CG3Se5) and a CuInGaSe2 (CIGSe2), with bandgaps 1.8eV and 1.1eV, were used as top and bottom cells, respectively.The research begins with a development of a lift-off process to exfoliate the single junction solar cell from its original substrate. Subjecting the device to substantial thermal or mechanical stresses results in cracking or pinhole formations, reducing absorber efficiency. Therefore, a gentle consistent method of removing high quality Cu(In,Ga)Se layer with minimum defects and maximum relative conversion efficiency before and after exfoliation is ideal. A simple mechanical exfoliation device was developed and tested in-situ. The system was capable of consistently exfoliating areas as large as 1 in2, the laboratory scale CG3Se5 sample, with minimum observable defects with the naked eye.Once successfully removed, an electrical back contact was applied onto the exfoliated surface of the CG3Se5 layer to compare the relative conversion efficiency as a measure of the quality of the exfoliated CG3Se5 layer. The relative conversion efficiency of the best single junction solar cell before and after the lift off process was found to be approximately 100% of the baseline efficiency, with short-circuit photocurrent density and open-circuit voltage preserved after exfoliation in independent devices with dimensions as large as 0.12 cm2.Once the maximum relative conversion efficiency for a single junction device was successfully achieved, the exfoliated single junction device was combined semi-monolithically with a fully processed CIGSe2 cell, creating a CG3Se5/CIGSe2 multi junction photovoltaic stack. The multi junction device of dimension 0.12 cm2 demonstrated 100% preservation of the limiting short circuit current density, and an above 90% open-circuit voltage of the sum of individual devices integrated into the multi junction device, with a fill factor of approximately 57%.Finally, the MJ device is further subjected to processing for the purpose of modifying the back contact. The electrical response of the MJ exfoliated device was measured and compared to its performance prior to exfoliation. Although exfoliation caused damage in the bottom cell, creating shunt pathways, electrically isolating the damaged portion of the cell from the operational area resulted in performance that is comparable to the cell performance before exfoliation.

ISBN: 9798535533407Subjects--Topical Terms:

586835
Engineering.
Subjects--Index Terms:

CIGS

Novel Semi-Monolithic Tandem Device Architecture for Photovoltaic and Photoelectrochemical Devices.
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500 $a Source: Masters Abstracts International, Volume: 83-03.
500 $a Advisor: Gaillard, Nicolas.
502 $a Thesis (M.S.)--University of Hawai'i at Manoa, 2021.
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520 $a Although silicon wafer based solar cells are dominant players in the market, with advanced technologies for large scale production, thin film technologies are studied for their potential in cost-reduction, higher efficiency, light weight, and flexible applications. Among the thin film technologies are the chalcopyrite based thin films, also known as Cu(In,Ga)Se based thin films.While single-junction Cu(In,Ga)Se efficiencies are nearing the performance of polycrystalline silicon, the solar irradiance wavelength range available for use to a single-junction solar cell is limited by the band gap energy of its absorber layer, resulting in inherent conversion efficiency limitations. To utilize a wider range of the solar spectrum, a tandem device utilizing multiple stacked solar cells of varying band gap energies is required. In addition to a wider spectrum absorption, a multi-junction device sums the open circuit voltage of each of the integrated sub-cells, allowing potential for photoelectrochemical water splitting for hydrogen production where voltages in excess of 1.5V are required. The produced hydrogen may be stored and used when sunlight is unavailable.Manufacturing single-junction Cu(In,Ga)Se typically involves layered deposition of elements onto a substrate such as molybdenum coated soda lime glass using vacuum vapor deposition. The p-type absorber Cu(In,Ga)Se requires high temperature for fabrication and annealing, while the n-type buffer layer required to make the p-n junction diode is produced at near room temperature. Because the high temperature annealing required to coarse grains size and fully form the absorber layer will melt the buffer layer and degrade its performance, or render the device inoperable, the manufacturing process is fabricated in the order of p-type absorber and n-type buffer for a single-junction device. During manufacturing tandem devices, the sequence of processing must ensure that the following steps will not destroy the underlying structure, as well as ensuring material compatibility between the top and bottom solar cells for optimal spectral absorption. This places limitations on the types of materials used for tandem devices and its manufacturing processes, leading to reduced performances. Traditional tandem device manufacturing, including monolithic and mechanical integration, lacks technological solutions to thoroughly overcome limitations in material selection and processing when applied to the chalcopyrite class.The proposed solution, the semi-monolithic tandem device architecture, is a novel lift-off and transfer method that allows for fabrication of single junction solar cells, as they are optimized, for subsequent integration with a separately processed cell. This method, once proven, could offer more freedom in material selection for tandem integration, and an easy adaptation of tandem devices to new single junction solar cell advancements.Because Cu(In,Ga)Se cells have unique material properties that facilitates the semi-monolithic manufacturing process, meet top and bottom cell requirements, as well as having one of the highest reported thin film solar cell conversion efficiency, this research focused on Cu(In,Ga)Se solar cells. A CuGa3Se5 (CG3Se5) and a CuInGaSe2 (CIGSe2), with bandgaps 1.8eV and 1.1eV, were used as top and bottom cells, respectively.The research begins with a development of a lift-off process to exfoliate the single junction solar cell from its original substrate. Subjecting the device to substantial thermal or mechanical stresses results in cracking or pinhole formations, reducing absorber efficiency. Therefore, a gentle consistent method of removing high quality Cu(In,Ga)Se layer with minimum defects and maximum relative conversion efficiency before and after exfoliation is ideal. A simple mechanical exfoliation device was developed and tested in-situ. The system was capable of consistently exfoliating areas as large as 1 in2, the laboratory scale CG3Se5 sample, with minimum observable defects with the naked eye.Once successfully removed, an electrical back contact was applied onto the exfoliated surface of the CG3Se5 layer to compare the relative conversion efficiency as a measure of the quality of the exfoliated CG3Se5 layer. The relative conversion efficiency of the best single junction solar cell before and after the lift off process was found to be approximately 100% of the baseline efficiency, with short-circuit photocurrent density and open-circuit voltage preserved after exfoliation in independent devices with dimensions as large as 0.12 cm2.Once the maximum relative conversion efficiency for a single junction device was successfully achieved, the exfoliated single junction device was combined semi-monolithically with a fully processed CIGSe2 cell, creating a CG3Se5/CIGSe2 multi junction photovoltaic stack. The multi junction device of dimension 0.12 cm2 demonstrated 100% preservation of the limiting short circuit current density, and an above 90% open-circuit voltage of the sum of individual devices integrated into the multi junction device, with a fill factor of approximately 57%.Finally, the MJ device is further subjected to processing for the purpose of modifying the back contact. The electrical response of the MJ exfoliated device was measured and compared to its performance prior to exfoliation. Although exfoliation caused damage in the bottom cell, creating shunt pathways, electrically isolating the damaged portion of the cell from the operational area resulted in performance that is comparable to the cell performance before exfoliation.
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