Guanidinium-Assisted Surface Matrix Engineering for Highly Efficient Perovskite Quantum Dot Photovoltaics

Xufeng Ling, Wanli Ma, Yuhang Wang, Jiabao Yang, Shaik Mohammed Zakeeruddin, Xiaoyu Zhang, Chunyang Zhang
2020
Article

Résumé

Metal halide perovskite quantum dots (Pe-QDs) are of great interest in new-generation photovoltaics (PVs). However, it remains challenging in the construction of conductive and intact Pe-QD films to maximize their functionality. Herein, a ligand-assisted surface matrix strategy to engineer the surface and packing states of Pe-QD solids is demonstrated by a mild thermal annealing treatment after ligand exchange processing (referred to as "LE-TA") triggered by guanidinium thiocyanate. The "LE-TA" method induces the formation of surface matrix on CsPbI3 QDs, which is dominated by the cationic guanidinium (GA(+)) rather than the SCN-, maintaining the intact cubic structure and facilitating interparticle electrical interaction of QD solids. Consequently, the GA-matrix-confined CsPbI3 QDs exhibit remarkably enhanced charge mobility and carrier diffusion length compared to control ones, leading to a champion power conversion efficiency of 15.21% when assembled in PVs, which is one of the highest among all Pe-QD solar cells. Additionally, the "LE-TA" method shows similar effects when applied to other Pe-QD PV systems like CsPbBr3 and FAPbI(3) (FA = formamidinium), indicating its versatility in regulating the surfaces of various Pe-QDs. This work may afford new guidelines to construct electrically conductive and structurally intact Pe-QD solids for efficient optoelectronic devices.

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https://infoscience.epfl.ch/record/277855?ln=fr

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Xufeng Ling, Wanli Ma, Yuhang Wang, Jiabao Yang, Shaik Mohammed Zakeeruddin, Xiaoyu Zhang, Chunyang Zhang
2020
Article

Résumé

Official source

https://infoscience.epfl.ch/record/277855?ln=fr

À propos de ce résultat

Concepts associés (5)

Concepts associés

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Publications associées (42)

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Over the last few years, thanks to rapid development of molecular engineering and perovskite composition, it has allowed extremely promising solar energy conversion to achieve a certified power conversion efficiency (PCE) of over 25% for perovskite solar cells (PSCs). However, there is always room for improvement in research for the long-term stability and high cost of PSCs, which are the major obstacles to the commercialization process, which can also be caused by organic materials and dopants. Thus, the work presented in this thesis is focused on synthesis, profound characterization and use of novel organic functional materials for PSCs. In addition, I aim to find synthetic guidelines that show how thoughtful molecular design, such as different atoms in molecular structure, different functional groups can have different effects on photovoltaic performance and long-term stability of PSCs.In this work, I introduced three novel hole-transporting materials (HTMs) with donor-bridge-acceptor design principle. Triazatruxene-based donor units were functionalized with terthiophene conjugated arms, then differentiated into CI-B1, CI-B2 and CI-B3 HTMs by linking strong electron-accepting units. All three HTMs showed intermolecular aggregation, especially CI-B3 molecules are packed in favor of well-ordered edge-on stacking. PSCs with triple cation perovskite in n-i-p architecture with dopant-free HTM CI-B3 showed an impressive PCE of 17.54% with a small hysteresis and improved long-term stability.Following up this work, the novel dopant-free HTM, CI-TTIN-2F, based on donor-bridge-acceptor, have been demonstrated for all-inorganic CsPbI3 PSCs. CI-TTIN-2F features intermolecular aggregation formed both face-on and edge-on orientation. Molecular dynamics (MD) calculations revealed the passivation effect of CI-TTIN-2F with Pb on the perovskite surface with different contact types. All-inorganic CsPbI3 PSCs with dopant-free CI-TTIN-2F HTM demonstrate a high PCE of 15.9%, along with 86% efficiency retention after 1000 hours. Moreover, the largest all-inorganic perovskite solar module was fabricated using the CI-TTIN-2F HTM, and exhibited PCE of 11.0% with an area of 27 cm2.As the next part of our work, three benzodipyrrole-based organic small-molecules functionalized with 4-methoxyphenyl (CB-1), 3-fluorophenyl (CB-2), and 3-trifluoromethylphenyl (CB-3) have been introduced as HTMs for PSCs. PL characteristics and MD simulations revealed the passivation effect of the CB-2 and CB-3 molecules on top of perovskite surface. The PSC using the highly planar CB-2 achieved the highest PCE of 18.23% with excellent long-term storage stability in the air without encapsulation, and the molecular hydrophobicity of the fluorinated HTMs ensured that the devices showed no degradation of their PCEs over 6 months. Finally, a novel passivation molecule with a phosphine oxide group providing a Lewis base, tris(5-((tetrahydro-2Hpyran-2-yl)oxy)pentyl)phosphine oxide (THPPO), has been employed at the HTM/perovskite interface. THPPO effectively passivated the undercoordinated Pb defect on the surface of the perovskite layer by forming a coordinate bond with P=O functional Lewis base. The HTM-free devices have confirmed significant increase in PCE from 5.84% to 13.31% with a significant improvement of the stability. Further, THPPO boosted PCE of the devices from 19.87% to 20.70% when combining the device with spiro-OMeTAD as an HTM.

EPFL2022

Chargement

Prediction of Photocurrent in Bifacial Photovoltaic Systems

Arttu Matias Tuomiranta

Motivated by the shift of the photovoltaic (PV) industry towards bifacial solar modules, desert markets, and ever narrower profit margins, this thesis study is aimed at improving the estimation accuracy of the output of bifacial PV systems that are potentially exposed to soiling. The scope is limited to the estimation of photocurrent, the performance parameter that is the most strongly affected by bifaciality and soiling. The thesis consists of three parts with the following topics: ground surface reflectance, module soiling, and bifacial effective irradiance. As for the first topic, the thesis aims at providing tools for surface reflectance estimation in any use case. The model evaluation results that are based on a global database of reflectance measurements can be used to choose a reflectance model that is appropriate for the surface type of interest. On a global average, the results show that data-driven estimation reduces the mean absolute error of reflectance estimates by 20-40% compared to the literature values. The proposed geographically generalised parametrisations of reflectance models can be used to produce temporally variable reflectance estimates if measuring campaigns for local model calibration cannot be implemented. If they can, the thesis provides detailed guidelines for their optimal timing. The choice of the reflectance model can result in deviations of up to 2.5% in the energy yield estimated for a bifacial PV system. In the second part of the thesis, a new physical model for forecasting soiling losses is proposed. The model incorporates new methods e.g., to simulate dust deposition on tilted surfaces, to physically capture the impact of relative humidity on dust accumulation, and to estimate the hemispherical transmittance of dust for diffuse light sources. The model can be used based on the public data products of numerical weather prediction models without the need for soiling measurements. The model is validated against its alternatives and measurements made at a field experiment in the United Arab Emirates. The impact of the soiling loss model on yield estimation is found to be lower than that of the reflectance model, plus minus 1% at maximum considering usual weekly or biweekly cleaning intervals. Finally, the third part of the thesis proposes a new model for simulating the photocurrent of each solar cell of a bifacial PV power plant using a computationally efficient method. It comprises a new algorithmic design that makes it possible to make all the detailed geometric calculations once and move to the temporal domain only to estimate irradiance. The most important novelty of the proposed model is that it estimates the photocurrent contributions as a distribution of the different light sources. The model is validated against the measurements made in France and Italy. The results of the validation show that the model's current estimates are more accurate than those of the widely used "unlimited sheds" approach. The most important reasons for the better performance are the new model's capability to estimate the spatial variability of effective irradiance on the array surface and that of ground-incident irradiance around the system. As per the impact assessment, the new model was found to overestimate yield and underestimate electricity cost by 1% on average. The "unlimited sheds" approach, in turn, resulted in more variable bias. In the case of large arrays, the approach was found to overestimate yield by 4%.

EPFL2020

Chargement

Effect of Selective Contacts on the Thermal Stability of Perovskite Solar Cells

Hui-Seon Kim, Xing Zhao

Thermal stability of CH3NH3PbT3 (MAPbI(3))based perovskite solar cells was investigated for normal structure including the mesoporous TiO2 layer and spiro-MeOTAD and the inverted structure with PCBM and NiO. MAPbI(3) was found to be intrinsically stable from 85 degrees C to 120 degrees C in the absence of moisture. However, fast degradation was observed for the encapsulated device including spiro-MeOTAD upon thermal stress at 85 degrees C. Photoluminescence (PL) intensity and the time constant for charge separation increased with thermal exposure time, which is indicative of inhibition of charge separation from MAPbI(3) into spiro-MeOTAD. A full recovery of photovoltaic performance was observed for the 85 degrees C-aged device after renewal with fresh spiro-MeOTAD, which clearly indicates that thermal instability of the normal structured device is mainly due to spiro-MeOTAD, and MAPbI(3) is proved to be thermally stable. Spiro-MeOTAD with additives was crystallized at 85 degrees C due to a low glass transition temperature, and hole mobility was significantly deteriorated, which was responsible for the thermal instability. Thermal stability was significantly improved for the inverted structure with the NiO hole transporting layer, where the power conversion efficiency (PCE) was maintained at 74% of its initial PCE of 14.71% after the 80th thermal cycle (one cycle: heating at 85 degrees C for 2 h and cooling at 25 degrees C for 2 h). This work implies that the thermal stability of perovskite solar cells depends on selective contacts.

Amer Chemical Soc2017

Chargement

Prediction of Photocurrent in Bifacial Photovoltaic Systems

Arttu Matias Tuomiranta

EPFL2020

EPFL2022