Towards the commercialization of colloidal quantum dot solar cells: perspectives on device structures and manufacturing

Lee, Hyunho; Song, Hyung‐Jun; Shim, Moonsub; Lee, Changhee

doi:10.1039/c9ee03348c

Cited by 80 publications

(72 citation statements)

References 222 publications

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“…Colloidal quantum dots (CQDs) are of interest in light‐emitting diodes,1,2 lasers,3 photodetectors,4 and solar cells5–14 owing to their tunable optical and electrical properties and their solution processing 15–18. Research efforts on surface passivation and device architecture have led to improvements in CQD solar cell performance,19–21 and these recently enabled power conversion efficiencies (PCE) above 12% for lead sulfide (PbS) CQDs 19…”

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confidence: 99%

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

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“…However, it also introduces drawbacks in view of its high density of trap states, [ 3 ] strong chemical interaction with the materials in the device stack, [ 4 ] and limited stability in encapsulated devices. [ 5 ] Importantly, it has a short diffusion length of tens of nm that precludes significant contribution to device photocurrent. [ 6 ]…”

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A Tuned Alternating D–A Copolymer Hole‐Transport Layer Enables Colloidal Quantum Dot Solar Cells with Superior Fill Factor and Efficiency

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Colloidal quantum dot solar cells (CQD-SCs) are attractive in view of their wide optoelectronic tunability and manufacturing benefits. [1] The power conversion efficiency (PCE) of CQD-SCs has seen rapid advances over the past decade, reaching a PCE of 13.3% through improvements in CQD surface chemistry and device architecture. [2] To date, the most efficient CQD-SCs consist (Figure 1a) of a thin electron transport/hole-blocking layer of zinc oxide deposited on indium-tin-oxide; an active layer, comprising a CQD solid passivated using halide atoms; and a thin hole-transport layer (HTL) of CQDs cross-linked with 1,2-ethanedithiol (EDT). The EDTtreated CQD layer as the HTL provides well-optimized energy alignment and a desirable electric field distribution within the active layer. However, it also introduces drawbacks in view of its high density of trap states, [3] strong chemical interaction with the materials in the device stack, [4] and limited stability in encapsulated devices. [5] Importantly, it has a short diffusion length of tens of nm that precludes significant contribution to device photocurrent. [6] An ideal HTL in PbS CQD-SCs should combine appropriate energy levels to allow efficient hole-extraction and electronblocking; [7] sufficient hole mobility for efficient vertical charge transport; [8] a diffusion length enabling contribution to the device photocurrent; [9] materials processing that is compatible with underlying layers in the CQD device; [10] and excellent morphology and conformal coverage to prevent oxygen and moisture permeation. [11] Recently, p-type polymers such as TQ1, P3HT, PDTPBT, and PBDB-TF have been explored as an alternative HTL to replace the EDT-treated CQD layer, but these have failed to render high performance due to unfavorable energy level alignment. [12-15] Benzodithiophene (BDT)-based HTL (PTB7), an alternative to P3HT, has been introduced as a potential HTL in PbS CQD-SCs. The use of PTB7 led to increased PCE due to more suitable energy levels and relatively improved hole-mobility compared to P3HT. Yet, PTB7-based devices still exhibited a limited PCE of 9.6%, [8] significantly lower than of state-of-art CQDs-SC with a PCE of 13.3%, [2] due to low hole mobility of 10 −4 cm 2 V −1 s −1

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“…Colloidal quantum dot solar cells (CQD-SCs) have attracted much attention owing to their solution-processability, ambient stability, and tunable bandgap. [1,2] Research efforts in device architecture and surface passivation have enabled power conversion efficiency (PCE) of 13.8%. [3] However, CQD-SCs still suffer from low open-circuit voltage (V OC ) and relatively weak absorption in the near-infrared (NIR) region.…”

Section: Doi: 101002/adma202004657mentioning

confidence: 99%

Monolithic Organic/Colloidal Quantum Dot Hybrid Tandem Solar Cells via Buffer Engineering

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Monolithically integrated hybrid tandem solar cells (TSCs) that combine solution‐processed colloidal quantum dot (CQD) and organic molecules are a promising device architecture, able to complement the absorption across the visible to the infrared. However, the performance of organic/CQD hybrid TSCs has not yet surpassed that of single‐junction CQD solar cells. Here, a strategic optical structure is devised to overcome the prior performance limit of hybrid TSCs by employing a multibuffer layer and a dual near‐infrared (NIR) absorber. In particular, a multibuffer layer is introduced to solve the problem of the CQD solvent penetrating the underlying organic layer. In addition, the matching current of monolithic TSCs is significantly improved to 15.2 mA cm−2 by using a dual NIR organic absorber that complements the absorption of CQD. The hybrid TSCs reach a power conversion efficiency (PCE) of 13.7%, higher than that of the corresponding individual single‐junction cells, representing the highest efficiency reported to date for CQD‐based hybrid TSCs.

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Towards the commercialization of colloidal quantum dot solar cells: perspectives on device structures and manufacturing

Abstract: A review towards the commercialization of colloidal quantum dot solar cells.

Cited by 80 publications

References 222 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

A Tuned Alternating D–A Copolymer Hole‐Transport Layer Enables Colloidal Quantum Dot Solar Cells with Superior Fill Factor and Efficiency

Monolithic Organic/Colloidal Quantum Dot Hybrid Tandem Solar Cells via Buffer Engineering

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