Publications by Hongwei Zhu | EPFL Graph Search

Molecularly Tailored Surface Defect Modifier for Efficient and Stable Perovskite Solar Cells

Miao Chen, Yelin Hu, Zhongjin Shen, Yinghui Wu, Shaik Mohammed Zakeeruddin, Hongwei Zhu

Surface defects cause non-radiative charge recombination and reduce the photovoltaic performance of perovskite solar cells (PSCs), thus effective passivation of defects has become a crucial method for achieving efficient and stable devices. Organic ammonium halides have been widely used for perovskite surface passivation, due to their simple preparation, lattice matching with perovskite, and high defects passivation ability. Herein, a surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is employed as the interfacial layer between the spiro-OMeTAD and perovskite layer to modify the surface defect states. It is found that TMBAI treatment suppresses the nonradiative charge carrier recombination, resulting in a 60 mV increase of the open-circuit voltage (V-oc) (from 1.11 to 1.17 V) and raises the fill factor from 76.3% to 80.3%. As a result, the TMBAI-based PSCs device demonstrates a power conversion efficiency (PCE) of 23.7%. Remarkably, PSCs with an aperture area of 1 square centimeter produce a PCE of 21.7% under standard AM1.5 G sunlight. The unencapsulated TMBAI-modified device retains 92.6% and 90.1% of the initial values after 1000 and 550 h under ambient conditions (humidity 55%-65%) and one-sun continuous illumination, respectively.

WILEY-V C H VERLAG GMBH2023

CNT-based bifacial perovskite solar cells towards highly efficient 4-terminal tandem photovoltaics

Fan Fu, Michael Graetzel, Shaik Mohammed Zakeeruddin, Chunyang Zhang, Hongwei Zhu

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

Thermophysical and thermomechanical properties of basalt-phenolic FRP rebars under high temperature

Thomas Keller, Ting Li, Jiahui Shen, Hongwei Zhu

An experimental investigation was conducted on the thermophysical and thermomechanical properties of phenolic-basalt fiber-reinforced polymer (P-BFRP) rebars subjected to high temperature. As a comparison, vinylBFRP (V-BFRP) and epoxy-BFRP (E-BFRP) rebars were also investigated within the same program. The mass variation of all BFRP rebar types was similar in air atmosphere while P-BFRP rebars decomposed more slowly in nitrogen atmosphere. All BFRP rebar types were found to have a similar specific heat and thermal conductivity up to 350 degrees C. P-BFRP rebars exhibited a much higher glass transition temperature compared with the other two types of BFRP rebars. Three failure modes could be differentiated for all BFRP rebar types according to three temperature ranges, the latter were shifted to higher values for P-BFRP rebars. No reduction in tensile strength occurred in P-BFRP rebars up to 300 degrees C, while V-BFRP and E-BFRP rebars experienced a significant degradation of tensile strength at around 100 degrees C already. This advantage of P-BFRP rebars was mainly caused by the much higher Tg which delayed the initiation of interfacial bonding failure up to 300 degrees C. The elastic modulus of all BFRP rebar types exhibited a similar degradation, which was caused by progressive fiber and fiber bundle failure due to non-uniform stress distributions.

ELSEVIER SCI LTD2022

Cyclopentadiene-Based Hole-Transport Material for Cost-Reduced Stabilized Perovskite Solar Cells with Power Conversion Efficiencies Over 23%

Michael Bauer, Thomas Paul Baumeler, Felix Thomas Eickemeyer, Michael Graetzel, Yuhang Liu, Shaik Mohammed Zakeeruddin, Hongwei Zhu

Hole transport materials (HTM) are an important component in perovskite solar cells (PSC). Despite a multitude of HTMs developed in recent years, only few of them lead to solar cells with efficiencies over 20%. Therefore, it is still a challenge to develop high-performing HTMs, which have ideal energy levels of the frontier orbitals, are highly efficient in transporting charges, and stabilize the solar cell at the same time. In this work, the development of a structurally novel molecular HTM, CPDA 1, is described which is based on a common cyclopentadiene core and can be efficiently and inexpensively synthesized from readily available starting materials, which is important for future realization of low-cost photovoltaics on larger scale. Due to excellent optoelectronic, thermal, and transport properties, CPDA 1 not only meets the envisioned properties by reaching high efficiencies of 23.1%, which is among the highest reported to date, but also contributes to a respectable long-term stability of the PSCs.

WILEY-V C H VERLAG GMBH2021

Methylamine Gas Treatment Affords Improving Semitransparency, Efficiency, and Stability of CH3NH3PbBr3-Based Perovskite Solar Cells

Michael Graetzel, Ajay Singh, Hongwei Zhu

High bandgap semitransparent solar cells based on CH3NH3PbBr3 perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH3NH3PbBr3 perovskite growth limit the exploitation of CH3NH3PbBr3-based perovskite solar cells. Herein, a post-treatment is carried out after the initial CH3NH3PbBr3 crystallization based on methylamine gas that drastically enhances the perovskite quality leading to a highly crystalline film with improved average visible transmittance (AVT) close to 56%. Opaque devices showed outstanding results in terms of open-circuit voltage and power conversion efficiency (PCE) reaching 1.54 V and 9.2%, respectively. These achievements are ascribed to a film with reduced morphological defects and better interface quality and reduced nonradiative pathways. For the first time, the fabrication of semitransparent CH3NH3PbBr3-based solar cells is demonstrated reaching a maximum PCE equal to 7.6%, an AVT of the full stack device of 52%, and an excellent light stability at maximum-power point tracking.

WILEY-V C H VERLAG GMBH2021

Macrophage NCOR1 Deficiency Ameliorates Myocardial Infarction and Neointimal Hyperplasia in Mice

Johan Auwerx, Yan Liu, Hongwei Zhu

Background NCOR1 (nuclear receptor corepressor 1) is an essential coregulator of gene transcription. It has been shown that NCOR1 in macrophages plays important roles in metabolic regulation. However, the function of macrophage NCOR1 in response to myocardial infarction (MI) or vascular wire injury has not been elucidated. Methods and Results Here, using macrophage Ncor1 knockout mouse in combination with a mouse model of MI, we demonstrated that macrophage NCOR1 deficiency significantly reduced infarct size and improved cardiac function after MI. In addition, macrophage NCOR1 deficiency markedly inhibited neointimal hyperplasia and vascular remodeling in a mouse model of arterial wire injury. Inflammation and macrophage proliferation were substantially attenuated in hearts and arteries of macrophage Ncor1 knockout mice after MI and arterial wire injury, respectively. Cultured primary macrophages from macrophage Ncor1 knockout mice manifested lower expression of inflammatory genes upon stimulation by interleukin-1 beta, interleukin-6, or lipopolysaccharide, together with much less activation of inflammatory signaling cascades including signal transducer and activator of transcription 1 and nuclear factor-kappa B. Furthermore, macrophage Ncor1 knockout macrophages were much less proliferative in culture, with inhibited cell cycle progression compared with control cells. Conclusions Collectively, our data have demonstrated that NCOR1 is a critical regulator of macrophage inflammation and proliferation and that deficiency of NCOR1 in macrophages attenuates MI and neointimal hyperplasia. Therefore, macrophage NCOR1 may serve as a potential therapeutic target for MI and restenosis.

2020

, , , , , , , , , ,

As a result of their attractive optoelectronic properties, metal halide APbI(3)perovskites employing formamidinium (FA(+)) as the A cation are the focus of research. The superior chemical and thermal stability of FA(+)cations makes alpha-FAPbI(3)more suitable for solar-cell applications than methylammonium lead iodide (MAPbI(3)). However, its spontaneous conversion into the yellow non-perovskite phase (delta-FAPbI(3)) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired alpha-FAPbI(3)perovskite phase by protecting it with a two-dimensional (2D) IBA(2)FAPb(2)I(7)(IBA=iso-butylammonium overlayer, formed via stepwise annealing. The alpha-FAPbI(3)/IBA(2)FAPb(2)I(7)based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 degrees C over 500 h.

WILEY-V C H VERLAG GMBH2020

Tailored Amphiphilic Molecular Mitigators for Stable Perovskite Solar Cells with 23.5% Efficiency

Brian Irving Carlsen, Mohammad Ibrahim Dar, Xiaofei Dong, Felix Thomas Eickemeyer, Ulf Anders Hagfeldt, Xiong Li, Yuhang Liu, Linfeng Pan, Dan Ren, Marco Alejandro Ruiz Preciado, Zaiwei Wang, Bowen Yang, Shaik Mohammed Zakeeruddin, Hongwei Zhu

Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.

2020

Efficient Perovskite Solar Cell Modules with High Stability Enabled by Iodide Diffusion Barriers

Michael Graetzel, Yuhang Wang, Tianhao Wu, Xianwei Zeng, Hongwei Zhu

Operational stability of efficient opto-electronic conversion is crucial for the success in large-scale application of perovskites devices. Owing to the intrinsically weak structure of perovskites, iodide represents the most volatile constituents, and its diffusion can induce irreversible degradation that continues to present a great challenge to realize stable perovskite devices, Here, we introduce a low-temperature processing strategy to increase the operational stability of high-efficiency perovskite solar modules by engineering low-dimensional diffusion barriers, reducing the unwanted interfacial diffusion of ions by 10(3)-10(7) times in magnitude. We finally achieved stable and efficient perovskite solar modules with an area of 36 cm(2) retaining over 95% of their initial efficiency of over 15% after 1,000 h of heating at 85 degrees C, and 91% after light soaking in AM 1.5 G solar light for 1,000 h, respectively. Our findings provide an effective strategy to realize operationally stable and efficient perovskite solar cell modules.

CELL PRESS2019

Impact of Peripheral Groups on Phenothiazine-Based Hole-Transporting Materials for Perovskite Solar Cells

Xiong Li, Hanlong Liu, Shaik Mohammed Zakeeruddin, Fei Zhang, Hongwei Zhu

2018