11 research outputs found
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Exceeding Conventional Photovoltaic Efficiency Limits Using Colloidal Quantum Dots
Colloidal quantum dots (QDs) are a widely investigated field of research due to their highly tunable nature in which the optical and electronic properties of the nanocrystal can be manipulated by merely changing the nanocrystalâs size. Specifically, colloidal quantum dot solar cells (QDSCs) have become a promising candidate for future generation photovoltaic technology. Quantum dots exhibit multiple exciton generation (MEG) in which multiple electron-hole pairs are generated from a single high-energy photon. This process is not observed in bulk-like semiconductors and allows for QDSCs to achieve theoretical efficiency limits above the standard single-junction Shockley-Queisser limit. However, the fast expanding field of QDSC research has lacked standardization of synthetic techniques and device design. Therefore, we sought to detail methodology for synthesizing PbS and PbSe QDs as well as photovoltaic device fabrication techniques as a fast track toward constructing high-performance solar cells. We show that these protocols lead toward consistently achieving efficiencies above 8% for PbS QDSCs.
Using the same methodology for building single-junction photovoltaic devices, we incorporated PbS QDs as a bottom cell into a monolithic tandem architecture along with solution-processed CdTe nanocrystals. Modeling shows that near-peak tandem device efficiencies can be achieved across a wide range of bottom cell band gaps, and therefore the highly tunable band gap of lead-chalcogenide QDs lends well towards a bottom cell in a tandem architecture. A fully functioning monolithic tandem device is realized through the development of a ZnTe/ZnO recombination layer that appropriately combines the two subcells in series.
Multiple recent reports have shown nanocrystalline heterostructures to undergo the MEG process more efficiency than several other nanostrucutres, namely lead-chalcogenide QDs. The final section of my thesis expands upon a recent publication by Zhang et. al., which details the synthesis of PbS/CdS heterostructures in which the PbS and CdS domains exist on opposite sides of the nanocrystal and are termed âJanus particlesâ. Transient absorption spectroscopy shows MEG quantum yields above unity very the thermodynamic limit of 2Eg for PbS/CdS Janus particles. We further explain a mechanism for enhanced MEG using photoluminescence studies
Recommended from our members
Exceeding Conventional Photovoltaic Efficiency Limits Using Colloidal Quantum Dots
Colloidal quantum dots (QDs) are a widely investigated field of research due to their highly tunable nature in which the optical and electronic properties of the nanocrystal can be manipulated by merely changing the nanocrystal’s size. Specifically, colloidal quantum dot solar cells (QDSCs) have become a promising candidate for future generation photovoltaic technology. Quantum dots exhibit multiple exciton generation (MEG) in which multiple electron-hole pairs are generated from a single high-energy photon. This process is not observed in bulk-like semiconductors and allows for QDSCs to achieve theoretical efficiency limits above the standard single-junction Shockley-Queisser limit. However, the fast expanding field of QDSC research has lacked standardization of synthetic techniques and device design. Therefore, we sought to detail methodology for synthesizing PbS and PbSe QDs as well as photovoltaic device fabrication techniques as a fast track toward constructing high-performance solar cells. We show that these protocols lead toward consistently achieving efficiencies above 8% for PbS QDSCs.
Using the same methodology for building single-junction photovoltaic devices, we incorporated PbS QDs as a bottom cell into a monolithic tandem architecture along with solution-processed CdTe nanocrystals. Modeling shows that near-peak tandem device efficiencies can be achieved across a wide range of bottom cell band gaps, and therefore the highly tunable band gap of lead-chalcogenide QDs lends well towards a bottom cell in a tandem architecture. A fully functioning monolithic tandem device is realized through the development of a ZnTe/ZnO recombination layer that appropriately combines the two subcells in series.
Multiple recent reports have shown nanocrystalline heterostructures to undergo the MEG process more efficiency than several other nanostrucutres, namely lead-chalcogenide QDs. The final section of my thesis expands upon a recent publication by Zhang et. al., which details the synthesis of PbS/CdS heterostructures in which the PbS and CdS domains exist on opposite sides of the nanocrystal and are termed “Janus particles”. Transient absorption spectroscopy shows MEG quantum yields above unity very the thermodynamic limit of 2Eg for PbS/CdS Janus particles. We further explain a mechanism for enhanced MEG using photoluminescence studies.</p
CsIâAntisolvent Adduct Formation in AllâInorganic Metal Halide Perovskites
The excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, highâperformance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the leadâhalide precursor salts. These adductâbased precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in allâinorganic perovskites such as CsPbI3. In this work, inorganic perovskite composition CsPbI3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other Aâsite cation salts. These CsI adducts control nucleation more so than the PbI2âdimethyl sulfoxide (DMSO) adduct and demonstrate how the Aâsite plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsIâMeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.It is found that unique adducts form between CsI and dimethyl sulfoxide (DMSO) and certain antisolvents, such as methyl acetate, during film formation of the allâinorganic perovskite CsPbI3. These adducts significantly influence crystallization and the power conversion efficiency of the resulting solar cells.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/1/aenm201903365-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/2/aenm201903365.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/3/aenm201903365_am.pd
CsIâAntisolvent Adduct Formation in AllâInorganic Metal Halide Perovskites
The excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, highâperformance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the leadâhalide precursor salts. These adductâbased precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in allâinorganic perovskites such as CsPbI3. In this work, inorganic perovskite composition CsPbI3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other Aâsite cation salts. These CsI adducts control nucleation more so than the PbI2âdimethyl sulfoxide (DMSO) adduct and demonstrate how the Aâsite plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsIâMeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.It is found that unique adducts form between CsI and dimethyl sulfoxide (DMSO) and certain antisolvents, such as methyl acetate, during film formation of the allâinorganic perovskite CsPbI3. These adducts significantly influence crystallization and the power conversion efficiency of the resulting solar cells.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/1/aenm201903365-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/2/aenm201903365.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/3/aenm201903365_am.pd
Quantum Dot Solar Cell Fabrication Protocols
Colloidally
synthesized quantum-confined semiconducting spherical
nanocrystals, often referred to as quantum dots (QDs), offer a high
degree of chemical, optical, and electronic tunability. As a result,
there is an increasing interest in employing colloidal QDs for electronic
and optical applications that is reflected in a growing number of
publications. In this protocol we provide detailed procedures for
the fabrication of QD solar cells specifically employing PbSe and
PbS QDs. We include details that are learned through experience, beyond
those in typical methodology sections, and include example pictures
and videos to aid in fabricating QD solar cells. Although
successful solar cell fabrication is ultimately learned through experience,
this protocol is intended to accelerate that process. The protocol
developed here is intended to be a general starting point for developing
PbS and PbSe QD test bed solar cells. We include steps for forming
conductive QD films via dip coating as well as spin coating. Finally,
we provide protocols that detail the synthesis of PbS and PbSe QDs
through a unique cation exchange reaction and discuss how different
QD synthetic routes could impact the resulting solar cell performance
Quantum Dot Solar Cell Fabrication Protocols
Colloidally
synthesized quantum-confined semiconducting spherical
nanocrystals, often referred to as quantum dots (QDs), offer a high
degree of chemical, optical, and electronic tunability. As a result,
there is an increasing interest in employing colloidal QDs for electronic
and optical applications that is reflected in a growing number of
publications. In this protocol we provide detailed procedures for
the fabrication of QD solar cells specifically employing PbSe and
PbS QDs. We include details that are learned through experience, beyond
those in typical methodology sections, and include example pictures
and videos to aid in fabricating QD solar cells. Although
successful solar cell fabrication is ultimately learned through experience,
this protocol is intended to accelerate that process. The protocol
developed here is intended to be a general starting point for developing
PbS and PbSe QD test bed solar cells. We include steps for forming
conductive QD films via dip coating as well as spin coating. Finally,
we provide protocols that detail the synthesis of PbS and PbSe QDs
through a unique cation exchange reaction and discuss how different
QD synthetic routes could impact the resulting solar cell performance
Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTeâZnO Tunnel Junction
We developed a monolithic
CdTeâPbS tandem solar cell architecture in which both the CdTe
and PbS absorber layers are solution-processed from nanocrystal inks.
Due to their tunable nature, PbS quantum dots (QDs), with a controllable
band gap between 0.4 and âŒ1.6 eV, are a promising candidate
for a bottom absorber layer in tandem photovoltaics. In the detailed
balance limit, the ideal configuration of a CdTe (<i>E</i><sub>g</sub> = 1.5 eV)âPbS tandem structure assumes infinite
thickness of the absorber layers and requires the PbS band gap to
be 0.75 eV to theoretically achieve a power conversion efficiency
(PCE) of 45%. However, modeling shows that by allowing the thickness
of the CdTe layer to vary, a tandem with efficiency over 40% is achievable
using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first
step toward developing this technology, we explore CdTeâPbS
tandem devices by developing a ZnTeâZnO tunnel junction, which
appropriately combines the two subcells in series. We examine the
basic characteristics of the solar cells as a function of layer thickness
and bottom-cell band gap and demonstrate open-circuit voltages in
excess of 1.1 V with matched short circuit current density of 10 mA/cm<sup>2</sup> in prototype devices