Michael Graetzel

Related publications (1,366)

Dataset of "The Impact of Spacer Size on Charge Transfer Excitons in Dion-Jacobson and Ruddlesden-Popper Layered Hybrid Perovskites"

Masaud Hassan S Almalki, George Cameron Fish, Michael Graetzel, Jacques-Edouard Moser, Lukas Pfeifer, Aaron Tomas Terpstra

This dataset underpins the following article published in the Journal of Physical Chemistry Letters: "The Impact of Spacer Size on Charge Transfer Excitons in Dion-Jacobson and Ruddlesden-Popper Layered Hybrid Perovskites" DOI: 10.1021/acs.jpclett.3c01125 The dataset contains steady state absorption (UV/Vis), transient absorption (TA) and electroabsorption (EA) data acquired from experiments on 2D perovskites incorporating different organic spacers. The dataset also includes data acquired from temperature dependent measurements. The transient absorption data has been treated using a home-written matlab script in order to correct for the chirp.

EPFL Infoscience2023

Exfoliated 2D Layered and Nonlayered Metal Phosphorous Trichalcogenides Nanosheets as Promising Electrocatalysts for CO2 Reduction

Michael Graetzel, Yelin Hu, Yunfei Jiao, Dan Ren, Chen Shen, Bing Wu, Hong Zhang

Two-dimensional (2D) materials catalysts provide an atomic-scale view on a fascinating arena for understanding the mechanism of electrocatalytic carbon dioxide reduction (CO2 ECR). Here, we successfully exfoliated both layered and nonlayered ultra-thin metal phosphorous trichalcogenides (MPCh(3)) nanosheets via wet grinding exfoliation (WGE), and systematically investigated the mechanism of MPCh(3) as catalysts for CO2 ECR. Unlike the layered CoPS3 and NiPS3 nanosheets, the active Sn atoms tend to be exposed on the surfaces of nonlayered SnPS3 nanosheets. Correspondingly, the nonlayered SnPS3 nanosheets exhibit clearly improved catalytic activity, showing formic acid selectivity up to 31.6 % with -7.51 mA cm(-2) at -0.65 V vs. RHE. The enhanced catalytic performance can be attributed to the formation of HCOO* via the first proton-electron pair addition on the SnPS3 surface. These results provide a new avenue to understand the novel CO2 ECR mechanism of Sn-based and MPCh(3)-based catalysts.

WILEY-V C H VERLAG GMBH2023

Optoelectronic or photovoltaic device with metal halide perovskite film treated by passivating agent

Michael Graetzel, Anurag Krishna, Lukas Pfeifer, Shaik Mohammed Zakeeruddin

This invention relates to an optoelectronic or photovoltaic device comprising a perovskite or metal halide perovskite film treated by one or more compounds of formula (I): ((R1-NH(R2)-R3)+)nW (I), wherein n is an integer selected from 1, 2, or 3; R1, R2, R3 are independently selected from a hydrocarbyl group containing 1-40 carbon atoms said hydrocarbyl group, if said hydrocarbyl group comprises 3 or more carbons, may be linear or branched; and W is an anion.

2023

Surface Passivation of FAPbI3-Rich Perovskite with Cesium Iodide Outperforms Bulk Incorporation

Essa Awadh R Alharbi, Thomas Paul Baumeler, Brian Irving Carlsen, Felix Thomas Eickemeyer, George Cameron Fish, Jing Gao, Michael Graetzel, Mounir Driss Mensi, Jacques-Edouard Moser, Lukas Pfeifer, Kevin Sivula, Jun Ho Yum, Shaik Mohammed Zakeeruddin

Metal halide perovskites (MHPs) have shown an incredible increase in efficiency, reaching as high as 25.7%, which now competes with traditional photovoltaic technologies. Herein, we excluded CsX and RbX (X = I–, Br–, Cl–), the most commonly used cations to stabilize α-FAPbI3, from the bulk of perovskite thin films and applied them on the surface as passivation agents. Extensive device optimization led to a power conversion efficiency (PCE) of 24.1% with a high fill factor (FF) of 82.2% upon passivation with CsI. We investigated in depth the effect of CsI passivation on structural and optoelectronic properties using X-ray diffraction (XRD), angle-resolved X-ray photoelectron spectroscopy (ARXPS), Kelvin probe force microscopy (KPFM), time-resolved photoluminescence (TRPL), photoluminescence quantum yield (PLQY), and electroabsorption spectroscopy (TREAS). Furthermore, passivated devices exhibit enhanced operational stability, with optimized passivation with CsI leading to a retention of ∼90% of the initial PCE under 1 sun illumination with maximum power point tracking for 600 h.

2023

The Impact of Spacer Size on Charge Transfer Excitons in Dion–Jacobson and Ruddlesden–Popper Layered Hybrid Perovskites

Masaud Hassan S Almalki, Loï Charles Carbone, Algirdas Ducinskas, George Cameron Fish, Michael Graetzel, Jovana Milic, Jacques-Edouard Moser, Lukas Pfeifer, Aaron Tomas Terpstra

Organic materials can tune the optical properties in layered (2D) hybrid perovskites, although their impact on photophysics is often overlooked. Here, we use transient absorption spectroscopy to probe the Dion−Jacobson (DJ) and Ruddlesden−Popper (RP) 2D perovskite phases. We show the formation of charge transfer excitons in DJ phases, resulting in a photoinduced Stark effect which is shown to be dependent on the spacer size. By using electroabsorption spectroscopy, we quantify the strength of the photoinduced electric field, while temperature-dependent measurements demonstrate new features in the transient spectra of RP phases at low temperatures resulting from the quantum-confined Stark effect. This study reveals the impact of spacer size and perovskite phase configuration on charge transfer excitons in 2D perovskites of interest to their advanced material design.

2023

A Molecularly Tailored Photosensitizer with an Efficiency of 13.2% for Dye-Sensitized Solar Cells

Naura Fakhira Antariksa, Felix Thomas Eickemeyer, Michael Graetzel, Zhongjin Shen, Shaik Mohammed Zakeeruddin

Photosensitizers yielding superior photocurrents are crucial for copper-electrolyte-based highly efficient dye-sensitized solar cells (DSCs). Herein, two molecularly tailored organic sensitizers are presented, coded ZS4 and ZS5, through judiciously employing dithieno[3,2-b:2 ",3 "-d]pyrrole (DTP) as the pi-linker and hexyloxy-substituted diphenylquinoxaline (HPQ) or naphthalene-fused-quinoxaline (NFQ) as the auxiliary electron-accepting unit, respectively. Endowed with the HPQ acceptor, ZS4 shows more efficient electron injection and charge collection based on substantially reduced interfacial charge recombination as compared to ZS5. As a result, ZS4-based DSCs achieve a power conversion efficiency (PCE) of 13.2% under standard AM1.5G sunlight, with a high short-circuit photocurrent density (J(sc)) of 16.3 mA cm(-2), an open-circuit voltage (V-oc) of 1.05 V and a fill factor (FF) of 77.1%. Remarkably, DSCs sensitized with ZS4 exhibit an outstanding stability, retaining 95% of their initial PCE under continuous light soaking for 1000 h. It is believed that this is a new record efficiency reported so far for copper-electrolyte-based DSCs using a single sensitizer. The work highlights the importance of developing molecularly tailored photosensitizers for highly efficient DSCs with copper electrolyte.

WILEY-V C H VERLAG GMBH2022

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Carbon-based perovskite solar cells (C-PSCs) are recognized as low-cost stable photovoltaics. However, currently most highly efficient C-PSCs are optically opaque, which means that they can only utilize direct illumination but cannot efficiently utilize the reflected irradiance. Here we propose bifacial C-PSCs incorporating transparent carbon-nanotube (CNT) network films in the rear electrode to efficiently utilize the reflected irradiation. By systematically optimizing the type and size of representative CNTs (including MWCNTs and SWCNTs), we find that the SWCNT-PSCs show a monofacial-power-conversion-efficiency (monofacial-PCE) of up to 21.4%, whereas the SWCNT-PSCs reach a bifacial power output of 24.0 mW cm−2 in natural reflecting surroundings (20% of AM 1.5 G irradiance) and 34.1 mW cm−2 in artificial reflecting surroundings (100% of AM 1.5 G irradiance). The bifacial SWCNT-PSCs also show high operational stability with a loss of 5% under 1000 h full sun continuous illumination. Moreover, we achieved a PCE of 27.1% by using our bifacial device as a top cell together with a CIS bottom cell in a 4-T tandem. These findings point to a promising direction for improving the output power per unit area of PSCs.

2022

Construction of Fe3O4 bridged Pt/g-C3N4 heterostructure with enhanced solar to fuel conversion

Michael Graetzel, Shaik Mohammed Zakeeruddin

In this study, we report the effects of co-catalysts of Pt nanoparticles and Fe3O4 clusters on photocatalytic behaviors of g-C3N4 (CN) and the use of the resulting photocatalyst for CO2 photoreduction to solar fuels in a flow reactor operated at room-temperature. In presence of H2O vapors, the selectivity of photogenerated electrons was emphasized, and found that the yield rate and selectivity of CH4 were improved by deposition of Pt on CN. With further inclusion of Fe3O4 over Pt/g-C3N4 (PtCN), the CH4 yield rate was significantly enhanced and H2 formation inhibited simultaneously, resulting in improved CH4 selectivity. Results show that the optimized Fe3O4/ Pt co-decorated CN (0.50 %FPtCN) heterostructure possesses significantly enhanced CO and CH4 yield rates of 1.83 mu molg- 1h- 1 and 0.532 mu molg- 1h- 1, respectively, which were 9 and 38 times superior to pure CN, attributed predominantly synergistic effects of Pt, Fe3O4, and CN. Owing to exceptional conductivity and electron-sink function, Pt NPs are an excellent electron transporter, which facilitates interfacial charges transfer and prohibits their recombination, while, the Fe3O4 clusters can synergistically promote the CO2 photoreduction by effectively using electrons as the oxidation - reduction center. Finally, insight obtained from results is used to propose a possible underlying mechanism for superior photocatalytic performance.

ELSEVIER2022

Hole transport material, synthesis thereof, and solar cell

Michael Bauer, Michael Graetzel, Yuhang Liu, Shaik Mohammed Zakeeruddin

The organic small molecule 4,4',4",4"'-(5,5-dimethoxycyclopenta-1,3-diene-1,2,3,4-tetrayl)tetrakis(N,N-bis(4-methoxyhenyl)aniline (CPDA 1), shows electrochemical properties very close to spiro-OMeTAD indicating a high compatibility with PSC systems for its use as a hole transport material (HTM). The implementation of the cyclopentadiene dimethyl acetale core helps to red shift the absorption onset of the films as well as provide a flexible spatial configuration of the molecule, which is essential for optimum film forming properties. Transient and steady state emission analysis as well as hole mobility measurements indicate that the new HTM allows a better charge extraction, transport and separation than the spiro-OMeTAD reference compound. PSCs based on the new CPDA 1 show a PCE close to 23% with lower hysteresis than its analogue. Stability studies performed under ambient, heated and humid conditions all showed that CPDA 1 is over-performing spiro-OMeTAD. Furthermore the production cost of CPDA 1 is about 10 times lower than that of spiro-OMeTAD, contributing to render PSCs more affordable.

2022

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The instability of rear electrodes undermines the long-term operational durability of efficient perovskite solar cells. Here, a composite electrode of copper-nickel (Cu-Ni) alloy stabilized by in situ grown bifacial graphene is designed. The alloying makes the work function of Cu suitable for regular perovskite solar cells. Cu-Ni is the ideal substrate for preparing high-quality graphene via chemical vapour deposition, which simultaneously protects the device from oxygen, water and reactions between internal components. To rivet the composite electrode with the semi-device, a thermoplastic copolymer is applied as an adhesive layer through hot pressing. The resulting devices achieve power conversion efficiencies of 24.34% and 20.76% (certified 20.86%) with aperture areas of 0.09 and 1.02 cm(2), respectively. The devices show improved stability: 97% of their initial efficiency is retained after 1,440 hours of a damp-heat test at 85 degrees C with a relative humidity of 85%; 95% of their initial efficiency is retained after 5,000 hours at maximum power point tracking under continuous 1 sun illumination. The instability of contact layers for perovskite solar cells under operating conditions limits the deployment of the technology. Now, Lin et al. develop a Cu-Ni electrode sandwiched between in situ-grown graphene protective layers, enabling solar cells with improved stability under light, humidity and high temperature.

NATURE PORTFOLIO2022