Spatial Collection in Colloidal Quantum Dot Solar Cells

Ouellette, Olivier; Lesage‐Landry, Antoine; Scheffel, Benjamin; Hoogland, Sjoerd; Arquer, F. Pelayo Garcı́a de; Sargent, Edward H.

doi:10.1002/adfm.201908200

Cited by 25 publications

(36 citation statements)

References 46 publications

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“…Details about the method and calculations of the SCE can be found in ref. 37. In brief, the Fredholm integral equation is used49,50

η (λ) = \int_{0}^{t} G (z, λ) ϕ (z) d z

where η(λ) is the IQE spectrum, t is the total thickness of the active layer, G ( z , λ) is the spectral photogeneration probability, and ϕ( z ) is the SCE.…”

Section: Methodsmentioning

confidence: 99%

“…The SCE reports the probability with which charge carriers generated within the device are collected at the electrodes and contribute to the output current (see Experimental Section for details) 37,39. In the best prior PbS CQD solar cell architecture (a), we observe a low collection efficiency for photocarriers generated near the interface between the active layer and the EDT HTL (Figure 1b, obtained from the internal quantum efficiency (IQE) and photogeneration probability in Figure S1, Supporting Information).…”

mentioning

confidence: 96%

“…Herein we seek experimental evidence of any role of the EDT HTL in performance; and we find, using a new spatial collection efficiency (SCE) technique,37 that the EDT HTL does indeed cause a rapid drop in the collection efficiency at the interface between HTL and active layer. We then develop an orthogonal CQD HTL that employs malonic acid (MA) instead of EDT.…”

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confidence: 99%

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A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells

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passivation and device architecture have led to improvements in CQD solar cell performance, [19][20][21] and these recently enabled power conversion efficiencies (PCE) above 12% for lead sulfide (PbS) CQDs. [19] The conventional CQD solar cell architecture consists of a transparent cathode, electron transport layer (ETL), a lightabsorbing active layer, a hole transport layer (HTL), and a metal anode. To achieve high-performing devices, the optoelectronic properties of the ETL, HTL, and active layer, which determine the charge absorption and extraction capacity of the devices, require accurate control. A number of excellent studies have illuminated the role of the ETL [22][23][24][25][26][27][28] and the active layer; [29] while the HTL is relatively less examined. Organic p-type semiconductors [30,31] and metal oxides (e.g., MoO 3 , NiO x , etc.) [32] have been explored to replace the thiol-passivated CQD HTL. Non-thiol ligands (e.g., NaHS) [33,34] have also been reported to produce p-type CQD solids; however, to date, device performance has not yet surpassed that of thiolpassivated CQD-based HTLs.State-of-art CQD solar cells employ 1,2-ethanedithiol (EDT) in the process of fabricating the CQD HTL. [19] This EDT HTL has been used in most high-performing CQD solar cells; but EDT has long been suspected of negatively affecting the underlying CQD active layer. In particular, its high reactivity [35] is proposed to be implicated in interfering with efficient charge extraction at the back-junction. [36] Herein we seek experimental evidence of any role of the EDT HTL in performance; and we find, using a new spatial collection efficiency (SCE) technique, [37] that the EDT HTL does indeed cause a rapid drop in the collection efficiency at the interface between HTL and active layer. We then develop an orthogonal CQD HTL that employs malonic acid (MA) instead of EDT. As a result of the lower reactivity of carboxylic acids compared to thiols, [38] the MA HTL substantially preserves the original surface chemistry of the CQD active layer after its deposition, as evidenced by X-ray photoelectron spectroscopy (XPS) analyses.The orthogonality of the MA HTL enables full charge collection at the back interface in CQD solar cells. This advance Colloidal quantum dots (CQDs) are of interest in light of their solutionprocessing and bandgap tuning. Advances in the performance of CQD optoelectronic devices require fine control over the properties of each layer in the device materials stack. This is particularly challenging in the present best CQD solar cells, since these employ a p-type hole-transport layer (HTL) implemented using 1,2-ethanedithiol (EDT) ligand exchange on top of the CQD active layer. It is established that the high reactivity of EDT causes a severe chemical modification to the active layer that deteriorates charge extraction. By combining elemental mapping with the spatial charge collection efficiency in CQD solar cells, the key materials interface dominating the subpar performance of prior CQD PV devices is demonstrat...

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“…Details about the method and calculations of the SCE can be found in ref. 37. In brief, the Fredholm integral equation is used49,50

η (λ) = \int_{0}^{t} G (z, λ) ϕ (z) d z

where η(λ) is the IQE spectrum, t is the total thickness of the active layer, G ( z , λ) is the spectral photogeneration probability, and ϕ( z ) is the SCE.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 96%

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A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells

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“…[18] Moreover, there are several reports that the PbS-EDT layer does not have low trap density and excellent carrier delivery compared to the iodide-treated PbS QD layer. [118] The introduction of QD thin films through new ligand treatment may improve these problems more easily because the PV structure that consists of the same QD film can carry free carriers by p-n junction structure with minimal Fresnel reflection.…”

Section: Resultsmentioning

confidence: 99%

Design Strategy of Quantum Dot Thin‐Film Solar Cells

Kim

Lim

Yun

et al. 2020

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Quantum dots (QDs) are emerging photovoltaic materials that display exclusive characteristics that can be adjusted through modification of their size and surface chemistry. However, designing a QD‐based optoelectronic device requires specialized approaches compared with designing conventional bulk‐based solar cells. In this paper, design considerations for QD thin‐film solar cells are introduced from two different viewpoints: optics and electrics. The confined energy level of QDs contributes to the adjustment of their band alignment, enabling their absorption characteristics to be adapted to a specific device purpose. However, the materials selected for this energy adjustment can increase the light loss induced by interface reflection. Thus, management of the light path is important for optical QD solar cell design, whereas surface modification is a crucial issue for the electrical design of QD solar cells. QD thin‐film solar cell architectures are fabricated as a heterojunction today, and ligand exchange provides suitable doping states and enhanced carrier transfer for the junction. Lastly, the stability issues and methods on QD thin‐film solar cells are surveyed. Through these strategies, a QD solar cell study can provide valuable insights for future‐oriented solar cell technology.

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“…Since their discovery in the 1980′s, semiconductor nanocrystals, also known as Quantum Dots (QDs) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], have gained much research attention. In particular, CdSe QDs are of interest due to their unique optical properties derived from quantum confinement and photoelectric conversion phenomena [ 17 , 18 ].…”

Section: Introductionmentioning

confidence: 99%

Monolayer Quantum-Dot Based Light-Sensor by a Photo-Electrochemical Mechanism

et al. 2020

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Monolayer nanocrystal-based light sensors with cadmium-selenium thin film electrodes have been investigated using electrochemical cyclic voltammetry tests. An indium tin oxide electrode system, with a monolayer of homogeneously deposited cadmium-selenium quantum dots was proven to work as a photo-sensor via an electrochemical cell mechanism; it was possible to tune current densities under light illumination. Electrochemical tests on a quantum dot capacitor, using different sized (red, yellow and green) cadmium-selenium quantum dots on indium tin oxide substrates, showed typical capacitive behavior of cyclic voltammetry curves in 2M H2SO4 aqueous solutions. This arrangement provides a beneficial effect in, both, charge separation and light sensory characteristics. Importantly, the photocurrent density depended on quantum yield rendering tunable photo-sensing properties.

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Spatial Collection in Colloidal Quantum Dot Solar Cells

Cited by 25 publications

References 46 publications

A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells

A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells

Design Strategy of Quantum Dot Thin‐Film Solar Cells

Monolayer Quantum-Dot Based Light-Sensor by a Photo-Electrochemical Mechanism

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