Essa Awadh R Alharbi

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

Compositional and interfacial optimization for enhancement of perovskite solar cells performance

Essa Awadh R Alharbi

Non-renewable sources are responsible for most of the overall greenhouse gas emissions, the development of sustainable energy sources is of prime importance to mitigate the negative effects of climate change. Among renewable sources, solar energy is one of the most abundant forms of energy available. Perovskite photovoltaics has emerged as one of the promising candidates for harvesting solar energy. However, these perovskite solar cells suffer from instability which is primarily due to the bulk and interface defects. In this thesis, we focus on the passivation of the bulk and interface defects to enable high-performance and stable devices. At the beginning of the thesis, we engineered the composition of mixed-cation and mixed-halide perovskite films by judicious incorporation of guanidinium iodide to suppress the parasitic charge carrier recombination, which enabled the fabrication of >20% efficient and operationally stable PSCs yielding reproducible photovoltage as high as 1.20 V. Thereafter, in our next project, we develop a facile strategy to reduce the level of electronic defects present at the interface between the perovskite film and the hole transport layer by treating the perovskite surface with different types of ammonium salts, namely ethylammonium, imidazolium, and guanidinium iodide. We find that this treatment boosts the power conversion efficiency from 20.5% for the control to 22.3%, 22.1%, and 21.0% for the devices treated with ethylammonium, imidazolium, and guanidinium iodide, respectively. Best performing devices showed a loss in efficiency of only 5% under full sunlight intensity with maximum power tracking for 550 h. We employed 2D-solid-state NMR (1H-1H correlation) spectroscopy to unravel the atomic-level mechanism of this passivation effect. Following that, we applied a facile and very effective method that employs methylammonium triiodide (MAI3) for bulk passivation together with interface passivation developed in the second project for holistic defect mitigation in perovskite solar cells. As a result, the champion device shows a power conversion efficiency (PCE) of 23.46% with a high fill factor (FF) of over 80%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining ~ 90% of its initial PCE under 1 Sun illumination with maximum power point tracking for 350 h. Finally, in our last project, we reconfigured the design of the alkylammonium halide salts to create a holistic bulk and interface engineering. We show that dimethylammonium head along with octyl chain and iodide counter anion works best in the bulk whereas dimethylammonium head along with octyl chain and fluoride counter anion works best at the interface. With a synergistic combination of both bulk and surface passivation, we achieved a high PCE of 24.91% along with exceptional long-term operational stability. In summary, in this thesis we employed different strategies based on organic ammonium salts to engineer the bulk and interface of the PSCs. We did an in-depth investigation of the optoelectronic properties, local structure, and molecular interactions with a combination of characterization at different length and time scales. Our results show that it is imperative to passivate both bulk and interface defects for obtaining high efficiency and stable solar cells. From our work, one can take inspiration from the design and analysis of new materials for the passivation of the PSCs.

EPFL2022

A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure alpha-FAPbI3

Paramvir Ahlawat, Essa Awadh R Alharbi, Haizhou Lu

It is well established that the lack of understanding the crystallization process in a two-step sequential deposition has a direct impact on efficiency, stability, and reproducibility of perovskite solar cells. Here, we try to understand the solid-solid phase transition occurring during the two-step sequential deposition of methylammonium lead iodide and formamidinium lead iodide. Using metadynamics, x-ray diffraction, and Raman spectroscopy, we reveal the microscopic details of this process. We find that the formation of perovskite proceeds through intermediate structures and report polymorphs found for methylammonium lead iodide and formamidinium lead iodide. From simulations, we discover a possible crystallization pathway for the highly efficient metastable α phase of formamidinium lead iodide. Guided by these simulations, we perform experiments that result in the low-temperature crystallization of phase-pure α-formamidinium lead iodide.

2021

Formation of High-Performance Multi-Cation Halide Perovskites Photovoltaics by delta-CsPbI3/delta-RbPbI3 Seed-Assisted Heterogeneous Nucleation

Essa Awadh R Alharbi, Masaud Hassan S Almalki, Thomas Paul Baumeler, Felix Thomas Eickemeyer, Ulf Anders Hagfeldt, Anurag Krishna, Mounir Driss Mensi, Olivier Ouellette, Linfeng Pan, Zaiwei Wang, Bowen Yang, Shaik Mohammed Zakeeruddin

The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi-cation halide composition of perovskite solar cells is engineered via the two-step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic delta-RbPbI3 and delta-CsPbI3 to the PbI2 precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI2 film. Thus, the subsequent conversion of PbI2 into the desired multication cubic alpha-structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the delta-CsPbI3 also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.

WILEY-V C H VERLAG GMBH2021

Methylammonium Triiodide for Defect Engineering of High-Efficiency Perovskite Solar Cells

Paramvir Ahlawat, Essa Awadh R Alharbi, Claudia Esther Avalos, Thomas Paul Baumeler, Mathias Dankl, Felix Thomas Eickemeyer, George Cameron Fish, Michael Graetzel, Ulf Anders Hagfeldt, Elsa John, Anurag Krishna, Mounir Driss Mensi, Jacques-Edouard Moser, Olivier Ouellette, Linfeng Pan, Lukas Pfeifer, Ursula Röthlisberger, Pascal Alexander Schouwink, Viktor Skorjanc, Bowen Yang, Shaik Mohammed Zakeeruddin

The defects present in metal halide perovskite are deleterious to both the performance and stability of photovoltaic devices. Consequently, there is an intense focus on developing defect mitigation strategies. Herein we report a facile strategy that employs methylammonium triiodide (MAI3) as an additive to the perovskite precursor solution. We examine the effect of MAI3 on the structural and optoelectronic properties by X-ray diffraction, density functional theory calculations, molecular dynamics simulations, solid-state nuclear magnetic resonance, steady-state, time-resolved photoluminescence (TRPL), and time-resolved terahertz spectroscopy (TRTS). Specifically, TRPL and TRTS show that MAI3 suppresses nonradiative recombination and increases the charge carrier mobility. As a result, the champion device shows a power conversion efficiency (PCE) of 23.46% with a high fill factor of >80%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining ∼90% of its initial PCE under 1 sun illumination with maximum power point tracking for 350 h.

2021

Atomic-Level Microstructure of Efficient Formamidinium-Based Perovskite Solar Cells Stabilized by 5-Ammonium Valeric Acid Iodide Revealed by Multinuclear and Two-Dimensional Solid-State NMR

Anwar Qasem M Alanazi, Essa Awadh R Alharbi, Marine Eva Fedora Bouduban, David Lyndon Emsley, Fabrizio Giordano, Michael Graetzel, Farzaneh Jahanbakhshi, Dominik Józef Kubicki, Jovana Milic, Marko Mladenovic, Jacques-Edouard Moser, Daniel Prochowicz, Dan Ren, Ursula Röthlisberger, Shaik Mohammed Zakeeruddin

Chemical doping of inorganic–organic hybrid perovskites is an effective way of improving the performance and operational stability of perovskite solar cells (PSCs). Here we use 5-ammonium valeric acid iodide (AVAI) to chemically stabilize the structure of α-FAPbI3. Using solid-state MAS NMR, we demonstrate the atomic-level interaction between the molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find that one-step deposition of the perovskite in the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. As a result, we achieve greatly enhanced solar cell performance for the optimized AVA-based devices with a maximum power conversion efficiency (PCE) of 18.94%. The devices retain 90% of the initial efficiency after 300 h under continuous white light illumination and maximum-power point-tracking measurement.

2019

Atomic-level passivation mechanism of ammonium salts enabling highly efficient perovskite solar cells

Anwar Qasem M Alanazi, Essa Awadh R Alharbi, Andrés Burgos Caminal, David Lyndon Emsley, Fabrizio Giordano, Dominik Józef Kubicki, Jingshan Luo, Jacques-Edouard Moser, Alexander Roland Uhl, Brennan James Walder, Shaik Mohammed Zakeeruddin

The high conversion efficiency has made metal halide perovskite solar cells a real break-through in thin film photovoltaic technology in recent years. Here, we introduce a straight-forward strategy to reduce the level of electronic defects present at the interface between the perovskite film and the hole transport layer by treating the perovskite surface with different types of ammonium salts, namely ethylammonium, imidazolium and guanidinium iodide. We use a triple cation perovskite formulation containing primarily formamidinium and small amounts of cesium and methylammonium. We find that this treatment boosts the power conversion efficiency from 20.5% for the control to 22.3%, 22.1%, and 21.0% for the devices treated with ethylammonium, imidazolium and guanidinium iodide, respectively. Best performing devices showed a loss in efficiency of only 5% under full sunlight intensity with maximum power tracking for 550 h. We apply 2D-solid-state NMR to unravel the atomic-level mechanism of this passivation effect.

2019

Performance of perovskite solar cells under simulated temperature-illumination real-world operating conditions

Anand Agarwalla, Essa Awadh R Alharbi, Brian Irving Carlsen, Konrad Domanski, Michael Graetzel, Ulf Anders Hagfeldt, Wolfgang Richard Tress

Since reaching 20% efficiency, research in perovskite photovoltaics has shifted from a race for efficiency to a race for stability. For efficiency, the standard test conditions set the rules for the race. However, the term 'stability' is used very broadly and assessed in various ways, meaning different groups are running different races. For the application, only energy yields that can be achieved under real-world, long-term operation matter. Here, we characterize and analyse the performance of an efficient perovskite solar cell (PSC) under simulated ambient conditions based on real temperature and irradiance data from selected days over one year at a location in central Europe. We find that the PSC shows only a low decrease of efficiency with elevated temperature and low light intensity, maintaining almost optimum values for ambient conditions, under which most of the solar energy is incident on the solar cell. The overall energy yield differs from what is expected from standard test condition measurements and is influenced by reversible degradation (delivering the highest performance in the morning) and by a slight permanent degradation that is observable during the year. With reference to tandem cells, we compare the PSC with a silicon device.

NATURE PUBLISHING GROUP2019

Perovskite Solar Cells Yielding Reproducible Photovoltage of 1.20 V

Essa Awadh R Alharbi, Neha Arora, Mohammad Ibrahim Dar, Michael Graetzel, Wolfgang Richard Tress, Pankaj Kumar Yadav, Shaik Mohammed Zakeeruddin

High photovoltages and power conversion efficiencies of perovskite solar cells (PSCs) can be realized by controlling the undesired nonradiative charge carrier recombination. Here, we introduce a judicious amount of guanidinium iodide into mixed-cation and mixed-halide perovskite films to suppress the parasitic charge carrier recombination, which enabled the fabrication of >20% efficient and operationally stable PSCs yielding reproducible photovoltage as high as 1.20 V. By introducing guanidinium iodide into the perovskite precursor solution, the bandgap of the resulting absorber material changed minimally; however, the nonradiative recombination diminished considerably as revealed by time-resolved photoluminescence and electroluminescence studies. Furthermore, using capacitance-frequency measurements, we were able to correlate the hysteresis features exhibited by the PSCs with interfacial charge accumulation. This study opens up a path to realize new record efficiencies for PSCs based on guanidinium iodide doped perovskite films.

2019

Essa Awadh R Alharbi

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

Compositional and interfacial optimization for enhancement of perovskite solar cells performance

A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure alpha-FAPbI3

Formation of High-Performance Multi-Cation Halide Perovskites Photovoltaics by delta-CsPbI3/delta-RbPbI3 Seed-Assisted Heterogeneous Nucleation

Methylammonium Triiodide for Defect Engineering of High-Efficiency Perovskite Solar Cells

Atomic-Level Microstructure of Efficient Formamidinium-Based Perovskite Solar Cells Stabilized by 5-Ammonium Valeric Acid Iodide Revealed by Multinuclear and Two-Dimensional Solid-State NMR

Atomic-level passivation mechanism of ammonium salts enabling highly efficient perovskite solar cells

Performance of perovskite solar cells under simulated temperature-illumination real-world operating conditions

Perovskite Solar Cells Yielding Reproducible Photovoltage of 1.20 V

Systematic investigation of the impact of operation conditions on the degradation behaviour of perovskite solar cells

Compositional and interfacial optimization for enhancement of perovskite solar cells performance

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

A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure alpha-FAPbI3

Atomic-level passivation mechanism of ammonium salts enabling highly efficient perovskite solar cells

Performance of perovskite solar cells under simulated temperature-illumination real-world operating conditions

Perovskite Solar Cells Yielding Reproducible Photovoltage of 1.20 V

Systematic investigation of the impact of operation conditions on the degradation behaviour of perovskite solar cells

Formation of High-Performance Multi-Cation Halide Perovskites Photovoltaics by delta-CsPbI3/delta-RbPbI3 Seed-Assisted Heterogeneous Nucleation

Methylammonium Triiodide for Defect Engineering of High-Efficiency Perovskite Solar Cells

Atomic-Level Microstructure of Efficient Formamidinium-Based Perovskite Solar Cells Stabilized by 5-Ammonium Valeric Acid Iodide Revealed by Multinuclear and Two-Dimensional Solid-State NMR