Defect Passivation of Low-Temperature Processed ZnO Electron Transport Layer with Polyethylenimine for PbS Quantum Dot Photovoltaics

Wang, Lei; Jia, Yuwen; Wang, Yinglin; Zang, Shuaipu; Wei, Shengsheng; Li, Jinhuan; Zhang, Xintong

doi:10.1021/acsaem.8b01756

Cited by 21 publications

(20 citation statements)

References 43 publications

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“…The OA-capped PbS CQDs were synthesized by the hot-injection method as described in our previous publication . The PTLE process of CQDs was executed under ambient conditions by the reported recipe with a slight modification .…”

Section: Methodsmentioning

confidence: 99%

“…The OA-capped PbS CQDs were synthesized by the hot-injection method as described in our previous publication. 11 The PTLE process of CQDs was executed under ambient conditions by the reported recipe with a slight modification. 5 PbI 2 (0.2 M) and PbBr 2 (0.04 M) and different concentrations of AA (0, 25, 50, 75 mM) were mixed and dissolved in N,N-dimethylformamide (DMF).…”

Section: ■ Methodsmentioning

confidence: 99%

“…Colloidal quantum dot solar cells (CQDSCs) based on lead chalcogenides (PbX; X = S, Se, or Te) could harvest solar photons in the range from the near- to mid-infrared region and possess advantages of size-tunable optical and electronic properties, good stability, and low-temperature solution processability. − This has led to CQDSCs emerging as outstanding candidates for the next-generation infrared photovoltaic and tandem photovoltaic devices to cover the absorption-edge shortage of crystalline silicon (1.1 eV) and perovskites (1.58 eV). − The principal process in the fabrication of CQDSCs involves the ligand exchange of the as-synthesized colloidal quantum dots (CQDs), which chemically replaces the highly insulating, long-chain oleic acid (OA) ligands by small ligands to promote the interdot electronic coupling in the CQD films. ,,− Ligand exchange used to be performed in solid-state CQD films, leading to CQDSCs being associated with serious problems including an appreciable residual of long-chain ligands and material consumption. ,− Recently, a phase-transfer ligand-exchange (PTLE) strategy was developed to conveniently produce a high-concentration solution of inorganic-ligand-capped PbS CQDs. ,,− It makes the fabrication of CQDSCs easy and dramatically promotes the photovoltaic performance of CQDSCs. ,− Consequently, the optimization of PTLE is of the essence for high-efficiency CQDSCs.…”

Section: Introductionmentioning

confidence: 99%

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Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

Wang

Jia

et al. 2019

J. Phys. Chem. C

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Chemical surface treatment of colloidal quantum dots (CQDs) by phase-transfer ligand-exchange (PTLE) is essential to implement highly densified, well-passivated CQD films for optoelectronic applications, such as infrared photovoltaics, light-emitting diodes, and photodetectors. PTLE, however, involves parallel and interactional processes of ligand exchange, phase transfer, and surface passivation of CQDs, which render the optimization of PTLE still challenging. Herein, we explored the action mechanism of a widely used additive, ammonium acetate (AA), on the PTLE of PbS CQDs to recognize the dynamic balance during the PTLE process and its impact on the performance of colloidal quantum dot solar cells (CQDSCs). Our research definitely shows that the AA additive can modify the dynamics of PTLE by participating in all of the three processes, and the amount of AA significantly influences the defect passivation and colloidal stability of PbS CQDs. At an appropriate concentration (∼50 mM) of AA, PbS CQDs are well iodide-passivated by PTLE, and the fabricated CQDSCs achieve a power conversion efficiency (PCE) of ∼10% associated with improved carrier transport and reduced trap-assisted carrier recombination. However, excessive AA causes trace residual AA on the CQD surface, resulting in the insufficient surface passivation of PbS CQDs and trap issues of CQDSCs. The double-edged sword effect of the AA additive on PTLE, demonstrated in our work, suggests that realizing a dynamic balance of different processes during PTLE is crucial for further performance promotion of CQDSCs.

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Section: Methodsmentioning

confidence: 99%

Section: ■ Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

Wang

Jia

et al. 2019

J. Phys. Chem. C

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“…[ 170 ] Similarly, ZnO energy level can be altered by polyethyleneimine (PEI) and chloride salt treatments, which can effectively reduce the ZnO defect density and improve the V oc of CQDSCs. [ 171,172 ] With n–i–p structure, the CQDSC with chloride salt treatment can achieve a V oc of 0.63 V, which is 20 mV higher than that without treatment (improved by 3.3%), and the V oc loss reduces to ≈0.403 V. [ 172 ]…”

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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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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“…When the valence band of the CQD active layer shifts to create closer alignment with the valence band of the EDT-doped HTL, a greater degree of retention of the free energy of carriers across interfaces corresponds to increased open-circuit voltage ( V OC ) . Recent efforts to improve the V OC of CQD solar cells have often targeted the ETL and HTL through doping , or the interface these layers share with the absorbing CQD active layer . Konstantatos et al show reductions in V OC losses are accomplished through suppressing carrier recombination in both the bulk and at the interface .…”

mentioning

confidence: 99%

Colloidal Quantum Dot Solar Cell Band Alignment using Two-Step Ionic Doping

Bertens

Fan

Biondi

et al. 2020

ACS Materials Lett.

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Colloidal quantum dot (CQD) solar cells composed of ionic halide passivated active layers benefit from improved passivation and high carrier mobility because of short interparticle distance. However, non-ideal band alignment of the active layer limits the potential open-circuit voltage (V OC) produced by the solar cell. We initiated a suite of simulation-based studies of CQD solar cells and found a route to improved performance by increasing the degree of p-type behavior. Fluoride, while it is a p-type ionic ligand as desired, is incompatible with traditional ligand exchange processes. In prior studies, it has shown to etch the lead sulfide surface uncontrollably. Instead, we develop a multistep halide exchange method, in which the CQD active layer is doped with fluoride ions after ligand exchange. This new method prevents CQD surface etching without impeding charge transport, resulting in a statistically significant improvement in V OC, fill factor, and power conversion efficiency.

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Defect Passivation of Low-Temperature Processed ZnO Electron Transport Layer with Polyethylenimine for PbS Quantum Dot Photovoltaics

Cited by 21 publications

References 43 publications

Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

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

Colloidal Quantum Dot Solar Cell Band Alignment using Two-Step Ionic Doping

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