Sulfur-Infused Hole Transport Materials to Overcome Performance-Limiting Transport in Colloidal Quantum Dot Solar Cells

Chiu, Arlene; Rong, Eric Phua Jian; Bambini, Christianna; Lin, Yida; Lu, Chengchangfeng; Thon, Susanna M.

doi:10.1021/acsenergylett.0c01586

Cited by 15 publications

(15 citation statements)

References 49 publications

(72 reference statements)

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“…[197,198] Recently, a sulfur-infused strategy was used to reduce stoichiometric imbalance and increase the p-type doping of EDT-PbS HTLs, but the V oc of the CQDSC only increased by ≈10 mV. [199] In addition to the doped EDT-PbS HTLs, p-type CQDs with larger bandgaps as HTLs can reduce the current in the reverse bias, thus reducing carrier recombination at the rear and improving the performance of CQDSCs. [200] The V oc of CQDSCs can be improved by using 1.38 eV EDT-PbS HTLs, but the PCE of the n-i-p structure is still relatively low, mainly due to the low V oc (0.45 V) and FF (below 50%).…”

Section: Cqd Htlsmentioning

confidence: 99%

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Open‐Circuit Voltage Loss in Lead Chalcogenide Quantum Dot Solar Cells

Liu

Xian

et al. 2021

Advanced Materials

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absorption coefficients, which can be used to capture the far-infrared of solar radiation. [13,14] This outperforms silicon-based and other solution-based semiconductor materials. Additionally, lead chalcogenide CQDSCs have the potential to break through the Shockley-Quesser limit, via multiple exciton generation. [15][16][17][18] In the past decade, lead chalcogenide CQDSCs have attracted abundant attention and their power conversion efficiencies (PCEs) have increased from ≈3% to ≈14%. [19][20][21] Moreover, the facile solution-processability (synthesis and ligand exchange) allows the production of solar cells by spraying, scraping, and roll-to-roll process, enabling great commercial potential. [22][23][24][25] Recently, some reports discussed the commercial viability of lead chalcogenide CQDSCs. [26,27] The results demonstrated that the cost of flexible lead chalcogenide CQDSCs can be as low as ≈0.94 $ per W, indicating the strong competitiveness of these solution-processability solar cells. To reach this low production cost, the PCEs of the CQDSCs are assumed to be 19% and the devices are assumed to be manufactured via a roll-toroll process. [27] Thus, it is still a great challenge for the commercialization of lead chalcogenide CQDSCs, and the low PCE is still the main obstacle for its market competitiveness.We summarize the main developments of lead chalcogenide CQDSCs (see Figure 1). In the early stage, the Schottky structure was used and it achieved the highest PCE of ≈5.2% in 2013. [28] But after 2014, there exist few reports of lead chalcogenide CQDSCs with the Schottky structure, due to the mismatch between optical absorption and charge extraction. [29] Subsequently, the n-p structure and depleted bulk heterojunction (DBH) structure have greatly improved the PCEs of lead chalcogenide CQDSCs. [30,31] N-p structure uses p-n junction to improve carrier extraction efficiency and reduce recombination, thus increasing the PCE of lead chalcogenide CQDSCs from ≈3% to above 9% in 2015. [19,32] Additionally, the absorption coefficient of lead chalcogenide CQDSCs reaches ≈10 6 cm −3 , which means that it is essential to use ≈1 μm solar absorber to fully absorb solar radiation. The DBH structure uses a bulk electron transport layer (ETL) to address the challenge of insufficient carrier diffusion length for the n-p structure, thus increasing the absorber thickness and greatly improving the short-circuit current (J sc ). [33][34][35] Through continued efforts, the PCE of the DBH structure has reached ≈10.8%. [36] To date, more research Lead chalcogenide colloidal quantum dot solar cells (CQDSCs) have received considerable attention due to their broad and tunable absorption and high stability. Presently, lead chalcogenide CQDSC has achieved a power conversion efficiency of ≈14%. However, the state-of-the-art lead chalcogenide CQDSC still has an open-circuit voltage (V oc ) loss of ≈0.45 V, which is significantly higher than those of c-Si and perovskite solar cells. Such high V oc loss severely limits the performance im...

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Section: Cqd Htlsmentioning

confidence: 99%

“…[ 197,198 ] Recently, a sulfur‐infused strategy was used to reduce stoichiometric imbalance and increase the p‐type doping of EDT‐PbS HTLs, but the V oc of the CQDSC only increased by ≈10 mV. [ 199 ]…”

Section: Charge Transport Layermentioning

confidence: 99%

Open‐Circuit Voltage Loss in Lead Chalcogenide Quantum Dot Solar Cells

Liu

Xian

et al. 2021

Advanced Materials

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“…This can be further improved, for example, by magnesium doping 48 or indium doping of ZnO. 49 On the hole transport (electron blocking) layer, a number of recent studies are exploring different organic molecules 50 and polymers. 51 Third, interfaces with contacts require consideration.…”

Section: ■ Conclusionmentioning

confidence: 99%

Recombination Dynamics in PbS Nanocrystal Quantum Dot Solar Cells Studied through Drift–Diffusion Simulations

Lin

Yazdani

Yarema

et al. 2021

ACS Appl. Electron. Mater.

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The significant performance increase in nanocrystal (NC)-based solar cells over the last decade is very encouraging. However, many of these gains have been achieved by trial-and-error optimization, and a systematic understanding of what limits the device performance is lacking. In parallel, experimental and computational techniques provide increasing insights into the electronic properties of individual NCs and their assemblies in thin films. Here, we utilize these insights to parameterize drift–diffusion simulations of PbS NC solar cells, which enable us to track the distribution of charge carriers in the device and quantify recombination dynamics, which limit the device performance. We simulate both Schottky- and heterojunction-type devices and, through temperature-dependent measurements in the light and dark, experimentally validate the appropriateness of the parameterization. The results reveal that Schottky-type devices are limited by surface recombination between the PbS and aluminum contact, while heterojunction devices are currently limited by NC dopants and electronic defects in the PbS layer. The simulations highlight a number of opportunities for further performance enhancement, including the reduction of dopants in the nanocrystal active layer, the control over doping and electronic structure in electron- and hole-blocking layers (e.g., ZnO), and the optimization of the interfaces to improve the band alignment and reduce surface recombination. For example, reduction in the percentage of p-type NCs from the current 1–0.01% in the heterojunction device can lead to a 25% percent increase in the power conversion efficiency.

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“…The device architecture of a QD solar cell consists of a transparent electrode, an n-type electron transport window layer (ETL), a light-absorbing active QD layer, a hole transport layer (HTL), and a metal electrode. , Several excellent advancements have been made to improve the ETL − and the active QD layer ,,,,− in the past. The development of a HTL to improve the performance of QD solar cells has gained significant research attention lately. − Several materials have been investigated for development of the HTL, including organic semiconductors, − metal oxides, − 2D semiconductors, , and p-type QDs. ,,,,, HTLs built using surface-functionalized p-doped QDs yield the highest photovoltaic performance to date. , …”

Section: Introductionmentioning

confidence: 99%

“…State-of-the-art HTLs are made by solid-state ligand exchange (SLE) of PbS QDs using 1,2-ethanethiol (EDT) as a ligand, first demonstrated by Luther et al in 2008 . There have been efforts to improve the PbS–EDT layer by fluorenylmethyloxycarbonyl-protected EDT, mixing EDT with potassium thiocyanate or 3-mercaptopropinoic acid, infusing sulfur into the PbS–EDT layer, and treatment by oxygen plasma. , In a typical SLE process, an oleic acid (OA)-capped native QD solution is spin-coated to grow a thin film, and the EDT ligand solution is then drop-casted and soaked for few seconds for the ligand exchange to complete. Finally, the film is washed with excess solvent to remove the unreacted ligands.…”

Section: Introductionmentioning

confidence: 99%

Crack-Free Conjugated PbS Quantum Dot–Hole Transport Layers for Solar Cells

Sharma

Dambhare

Bera

et al. 2021

ACS Appl. Nano Mater.

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Colloidal quantum dots (QDs) benefit from solution-phase processing and band-gap tuning for their application in solar cell development. Today's QD solar cells rely on solid-state ligand exchange (SLE) to replace bulky oleic acid (OA) ligands with small 1,2-ethanedithiol (EDT) ligands to develop a conducting hole transport layer (HTL). High volume contraction in EDT conjugated QD films, however, leads to crack and porosity in the HTL, which is a major cause of concern for the device reproducibility and large-area solar cell development. We show that partial removal of the OA ligands in the solution phase reduces the volume contraction in solid films, thereby allowing the growth of crack-free QD films in the SLE process. The cleaning of QDs by repeated precipitation and redispersion using a protic methanol (MeOH) solvent helps with partial removal of the OA ligands, but it is detrimental to the electronic properties of QDs. We develop a one-step solution-phase partial ligand-exchange process using ammonium salts, which enable partial replacement of the OA ligands and passivation of the QD surface. Introduction of the facile partial ligand-exchange process eliminates the need for tedious and wasteful multiple cleaning steps with MeOH, while improving the photophysical properties of QDs. The advancement in QD processing helps to build crackfree, smooth, and conjugated QD films for their deployment as HTLs in solar cell development. Partial ligand exchange with NH 4 SCN leads to a 1.5 times increase in p doping and mobility over multiple MeOH-cleaned PbS QD films. HTLs developed using NH 4 SCN QDs show an improved photovoltaic performance to attain a 10.5% power conversion efficiency. Improvement in the depletion width and hole collection efficiency leads to a superior photovoltaic performance, as confirmed from experimental studies and one-dimensional solar cell capacitance simulation.

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Sulfur-Infused Hole Transport Materials to Overcome Performance-Limiting Transport in Colloidal Quantum Dot Solar Cells

Cited by 15 publications

References 49 publications

Open‐Circuit Voltage Loss in Lead Chalcogenide Quantum Dot Solar Cells

Open‐Circuit Voltage Loss in Lead Chalcogenide Quantum Dot Solar Cells

Recombination Dynamics in PbS Nanocrystal Quantum Dot Solar Cells Studied through Drift–Diffusion Simulations

Crack-Free Conjugated PbS Quantum Dot–Hole Transport Layers for Solar Cells

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