Lead Selenide (PbSe) Colloidal Quantum Dot Solar Cells with &gt;10% Efficiency

Ahmad, Waqar; He, Jungang; Liu, Zhitian; Xu, Ke; Chen, Zhuang; Yang, Xiaokun; Li, Deng‐Bing; Xia, Yong; Zhang, Jianbing; Chen, Chao

doi:10.1002/adma.201900593

Cited by 93 publications

(108 citation statements)

References 45 publications

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“…In order to explore energetic disorder in the PbS QD solids, we adopt the tail state absorption to estimate the Urbach energy. [ 26,40 ] The o ‐PbS QD solid exhibits a lower Urbach energy of 28.6 meV than the to ‐QD solid (38.5 meV), indicating a lower trap density and fewer tail states in the QD solids with smaller {100} facets. Furthermore, the o ‐PbS QD solids show a shallower bandtail, demonstrated by the smaller redshift of the transient bleach peak in the spectrotemporal transient absorption (TA) map as shown in Figure 4e,f.…”

Section: Resultsmentioning

confidence: 99%

Facet Control for Trap‐State Suppression in Colloidal Quantum Dot Solids

Xia

Chen

Zhang

et al. 2020

Adv Funct Materials

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Trap states in colloidal quantum dot (QD) solids significantly affect the performance of QD solar cells, because they limit the open-circuit voltage and short circuit current. The {100} facets of PbS QDs are important origins of trap states due to their weak or missing passivation. However, previous investigations focused on synthesis, ligand exchange, or passivation approaches and ignored the control of {100} facets for a given dot size. Herein, trap states are suppressed from the source via facet control of PbS QDs. The {100} facets of ≈3 nm PbS QDs are minimized by tuning the balance between the growth kinetics and thermodynamics in the synthesis. The PbS QDs synthesized at a relatively low temperature with a high oversaturation follow a kinetics-dominated growth, producing nearly octahedral nanoparticles terminated mostly by {111} facets. In contrast, the PbS QDs synthesized at a relatively high temperature follow a thermodynamics-dominated growth. Thus, a spherical shape is preferred, producing truncated octahedral nanoparticles with more {100} facets. Compared to PbS QDs from thermodynamics-dominated growth, the PbS QDs with less {100} facets show fewer trap states in the QD solids, leading to a better photovoltaic device performance with a power conversion efficiency of 11.5%.

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Section: Resultsmentioning

confidence: 99%

Facet Control for Trap‐State Suppression in Colloidal Quantum Dot Solids

Xia

Chen

Zhang

et al. 2020

Adv Funct Materials

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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

et al. 2020

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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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“…The measured surface roughness was Rmax = 1.47, Rq = 0.283, and Ra = 0.224 nm. The AFM results reveal that the samples have a very smooth surface and that the roughness was very low, which indicates that the oligomer films can be self-assembled and it suitable for various devices such as solar cells [35,36], Organic Light Emitting Diodes (OLEDs) [37] and lasers [38]. The low amount of surface defects is ideal for a laser material because they facilitate low speckle formation and very low scattering loss and could become a good planar waveguide that allows surface laser emission.…”

Section: Atomic Force Microscopy (Afm)mentioning

confidence: 99%

Narrowband Spontaneous Emission Amplification from a Conjugated Oligomer Thin Film

2020

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In this paper, we studied the laser and optical properties of conjugated oligomer (CO) 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF) thin films, which were cast onto a quartz substrate using a spin coating technique. BECV-DHF was dissolved in chloroform at different concentrations to produce thin films with various thicknesses. The obtained results from the absorption spectrum revealed one sharp peak at 403 nm and two broads at 375 and 428 nm. The photoluminescence (PL) spectra were recorded for different thin films made from different concentrations of the oligomer solution. The threshold, laser-induced fluorescence (LIF), and amplified spontaneous emission (ASE) properties of the CO BECV-DHF thin films were studied in detail. The ASE spectrum was achieved at approximately 482.5 nm at a suitable concentration and sufficient pump energy. The time-resolved spectroscopy of the BECV-DHF films was demonstrated at different pump energies.

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Lead Selenide (PbSe) Colloidal Quantum Dot Solar Cells with >10% Efficiency

Cited by 93 publications

References 45 publications

Facet Control for Trap‐State Suppression in Colloidal Quantum Dot Solids

Facet Control for Trap‐State Suppression in Colloidal Quantum Dot Solids

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

Narrowband Spontaneous Emission Amplification from a Conjugated Oligomer Thin Film

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