Browsing by Author "Saliba, Michael"

Now showing 1 - 15 of 15

Open Access
All-inorganic CsPbI2Br perovskite solar cells with thermal stability at 250 °C and moisture-resilience via polymeric protection layers
(2025) Roy, Rajarshi; Byranvand, Mahdi Malekshahi; Zohdi, Mohamed Reza; Magorian Friedlmeier, Theresa; Das, Chittaranjan; Hempel, Wolfram; Zuo, Weiwei; Kedia, Mayank; Rendon, Jose Jeronimo; Boehringer, Stephan; Hailegnanw, Bekele; Vorochta, Michael; Mehl, Sascha; Rai, Monika; Kulkarni, Ashish; Mathur, Sanjay; Saliba, Michael
All-inorganic perovskites, such as CsPbI2Br, have emerged as promising compositions due to their enhanced thermal stability. However, they face significant challenges due to their susceptibility to humidity. In this work, CsPbI2Br perovskite is treated with poly(3-hexylthiophen-2,5-diyl) (P3HT) during the crystallization resulting in significant stability improvements against thermal, moisture and steady-state operation stressors. The perovskite solar cell retains ∼90% of the initial efficiency under relative humidity (RH) at ∼60% for 30 min, which is among the most stable all-inorganic perovskite devices to date under such harsh conditions. Furthermore, the P3HT treatment ensures high thermal stress tolerance at 250 °C for over 5 h. In addition to the stability enhancements, the champion P3HT-treated device shows a higher power conversion efficiency (PCE) of 13.5% compared to 12.7% (reference) with the stabilized power output (SPO) for 300 s. In addition, the P3HT-protected perovskite layer in ambient conditions shows ∼75% of the initial efficiency compared to the unprotected devices with ∼28% of their initial efficiency after 7 days of shelf life.
Open Access
All-perovskite tandem solar cells : from fundamentals to technological progress
(2024) Lim, Jaekeun; Park, Nam-Gyu; Seok, Sang Il; Saliba, Michael
Organic-inorganic perovskite materials have gradually progressed from single-junction solar cells to tandem (double) or even multi-junction (triple-junction) solar cells as all-perovskite tandem solar cells (APTSCs). Perovskites have numerous advantages: (1) tunable optical bandgaps, (2) low-cost, e.g. via solution-processing, inexpensive precursors, and compatibility with many thin-film processing technologies, (3) scalability and lightweight, and (4) eco-friendliness related to low CO2 emission. However, APTSCs face challenges regarding stability caused by Sn2+ oxidation in narrow bandgap perovskites, low performance due to Voc deficit in the wide bandgap range, non-standardisation of charge recombination layers, and challenging thin-film deposition as each layer must be nearly perfectly homogenous. Here, we discuss the fundamentals of APTSCs and technological progress in constructing each layer of the all-perovskite stacks. Furthermore, the theoretical power conversion efficiency (PCE) limitation of APTSCs is discussed using simulations.
Open Access
Characterizing the influence of charge extraction layers on the performance of triple‐cation perovskite solar cells
(2023) Siekmann, Johanna; Kulkarni, Ashish; Akel, Samah; Klingebiel, Benjamin; Saliba, Michael; Rau, Uwe; Kirchartz, Thomas
Selecting suitable charge transport layers and suppressing non-radiative recombination at interfaces with the absorber layer is vital for maximizing the efficiency of halide perovskite solar cells. In this study, high-quality perovskite thin films and devices are fabricated with different fullerene-based electron transport layers and different self-assembled monolayers as hole transport layers. Then, a comparative study of a significant variety of different electrical, optical, and photoemission-based characterization techniques is performed to quantify the properties of the solar cells, individual layers, and, importantly, the interfaces between them. In addition, the limitations and problems of the different measurements, the insights gained by combining different methods, and the different strategies for extracting information from the experimental raw data, are highlighted.
Open Access
Coordination chemistry as a universal strategy for a controlled perovskite crystallization
(2023) Zuo, Weiwei; Byranvand, Mahdi Malekshahi; Kodalle, Tim; Zohdi, Mohammadreza; Lim, Jaekeun; Carlsen, Brian; Magorian Friedlmeier, Theresa; Kot, Małgorzata; Das, Chittaranjan; Flege, Jan Ingo; Zong, Wansheng; Abate, Antonio; Sutter‐Fella, Carolin M.; Li, Meng; Saliba, Michael
The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.
Open Access
High‐stable lead‐free solar cells achieved by surface reconstruction of quasi‐2D tin‐based perovskites
(2023) Yang, Feng; Zhu, Rui; Zhang, Zuhong; Su, Zhenhuang; Zuo, Weiwei; He, Bingchen; Aldamasy, Mahmoud Hussein; Jia, Yu; Li, Guixiang; Gao, Xingyu; Li, Zhe; Saliba, Michael; Abate, Antonio; Li, Meng
Tin halide perovskites are an appealing alternative to lead perovskites. However, owing to the lower redox potential of Sn(II)/Sn(IV), particularly under the presence of oxygen and water, the accumulation of Sn(IV) at the surface layer will negatively impact the device's performance and stability. To this end, this work has introduced a novel multifunctional molecule, 1,4‐phenyldimethylammonium dibromide diamine (phDMADBr), to form a protective layer on the surface of Sn‐based perovskite films. Strong interactions between phDMADBr and the perovskite surface improve electron transfer, passivating uncoordinated Sn(II), and fortify against water and oxygen. In situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) analysis confirms the enhanced thermal stability of the quasi‐2D phase, and hence the overall enhanced stability of the perovskite. Long‐term stability in devices is achieved, retaining over 90% of the original efficiency for more than 200 hours in a 10% RH moisture N2 environment. These findings propose a new approach to enhance the operational stability of Sn‐based perovskite devices, offering a strategy in advancing lead‐free optoelectronic applications.
Open Access
Ionic liquid Stabilizing high‐efficiency tin halide perovskite solar cells
(2021) Li, Guixiang; Su, Zhenhuang; Li, Meng; Yang, Feng; Aldamasy, Mahmoud H.; Pascual, Jorge; Yang, Fengjiu; Liu, Hairui; Zuo, Weiwei; Di Girolamo, Diego; Iqbal, Zafar; Nasti, Giuseppe; Dallmann, André; Gao, Xingyu; Wang, Zhaokui; Saliba, Michael; Abate, Antonio
Tin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.
Open Access
Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina
(2025) Kedia, Mayank; Das, Chittaranjan; Kot, Malgorzata; Yalcinkaya, Yenal; Zuo, Weiwei; Tabah Tanko, Kenedy; Matvija, Peter; Ezquer, Mikel; Cornago, Iñaki; Hempel, Wolfram; Kauffmann, Florian; Plate, Paul; Lira-Cantu, Monica; Weber, Stefan A. L.; Saliba, Michael
Atomic layer deposition of aluminum oxide (ALD-Al2O3) layers has recently been studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al2O3 layer acts as a protective barrier, mitigating pernicious halide ion migration from the perovskite towards the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (∼0.75 nm) ALD-Al2O3 layer that conformally coats the morphology of a triple-cation perovskite layer. This promotes an effective contact of the hole transporter layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC, we discovered that ALD-Al2O3 also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to these protective considerations, ALD-Al2O3 impedes the transition of crystalline perovskites to an undesired amorphous phase. Consequently, the dual functionality (i.e., enhanced contact and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1% to 20.5%, while retaining 98% of its initial performance compared to <10% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al2O3 as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs.
Open Access
One‐step thermal gradient‐ and antisolvent‐free crystallization of all‐inorganic perovskites for highly efficient and thermally stable solar cells
(2022) Byranvand, Mahdi Malekshahi; Kodalle, Tim; Zuo, Weiwei; Magorian Friedlmeier, Theresa; Abdelsamie, Maged; Hong, Kootak; Zia, Waqas; Perween, Shama; Clemens, Oliver; Sutter‐Fella, Carolin M.; Saliba, Michael
All‐inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their heat‐sensitive hybrid organic–inorganic counterparts. In particular, CsPbI2Br shows the highest potential for developing thermally‐stable perovskite solar cells (PSCs) among all‐inorganic compositions. However, controlling the crystallinity and morphology of all‐inorganic compositions is a significant challenge. Here, a simple, thermal gradient‐ and antisolvent‐free method is reported to control the crystallization of CsPbI2Br films. Optical in situ characterization is used to investigate the dynamic film formation during spin‐coating and annealing to understand and optimize the evolving film properties. This leads to high‐quality perovskite films with micrometer‐scale grain sizes with a noteworthy performance of 17% (≈16% stabilized), fill factor (FF) of 80.5%, and open‐circuit voltage (VOC) of 1.27 V. Moreover, excellent phase and thermal stability are demonstrated even after extreme thermal stressing at 300 °C.
Open Access
Photoelectrochemical water‐splitting using CuO‐based electrodes for hydrogen production : a review
(2021) Siavash Moakhar, Roozbeh; Hosseini‐Hosseinabad, Seyed Morteza; Masudy‐Panah, Saeid; Seza, Ashkan; Jalali, Mahsa; Fallah‐Arani, Hesam; Dabir, Fatemeh; Gholipour, Somayeh; Abdi, Yaser; Bagheri‐Hariri, Mohiedin; Riahi‐Noori, Nastaran; Lim, Yee‐Fun; Hagfeldt, Anders; Saliba, Michael
The cost‐effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water‐splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO‐based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water‐splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO‐based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent‐generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.
Open Access
Pure tin halide perovskite solar cells : focusing on preparation and strategies
(2022) Liu, Hairui; Zhang, Zuhong; Zuo, Weiwei; Roy, Rajarshi; Li, Meng; Byranvand, Mahdi Malekshahi; Saliba, Michael
Metal halide perovskite solar cells (PSCs) have emerged as an important direction for photovoltaic research. Although the power conversion efficiency (PCE) of lead‐based PSCs has reached 25.7%, still the toxicity of Pb remains one main obstacle for commercial adoption. Thus, to address this issue, Pb‐free perovskites have been proposed. Among them, tin‐based perovskites have emerged as promising candidates. Unfortunately, the fast oxidation of Sn2+ to Sn4+ leads to low stability and efficiency. Many strategies have been implemented to address these challenges in Sn‐based PSCs. This work introduces stability and efficiency improvement strategies for pure Sn‐based PSCs by optimization of the crystal structure, processing and interfaces as well as, implementation of low‐dimension structures. Finally, new perspectives for further developing Sn‐based PSCs are provided.
Open Access
Top‐down approach to study chemical and electronic properties of perovskite solar cells : sputtered depth profiling versus tapered cross‐sectional photoelectron spectroscopies
(2021) Das, Chittaranjan; Zia, Waqas; Mortan, Claudiu; Hussain, Navid; Saliba, Michael; Ingo Flege, Jan; Kot, Małgorzata
A study of the chemical and electronic properties of various layers across perovskite solar cell (PSC) stacks is challenging. Depth‐profiling photoemission spectroscopy can be used to study the surface, interface, and bulk properties of different layers in PSCs, which influence the overall performance of these devices. Herein, sputter depth profiling (SDP) and tapered cross‐sectional (TCS) photoelectron spectroscopies (PESs) are used to study highly efficient mixed halide PSCs. It is found that the most used SDP‐PES technique degrades the organic and deforms the inorganic materials during sputtering of the PSCs while the TCS‐PES method is less destructive and can determine the chemical and electronic properties of all layers precisely. The SDP‐PES dissociates the chemical bonding in the spiro‐MeOTAD and perovskite layer and reduces the TiO2, which causes the chemical analysis to be unreliable. The TCS‐PES revealed a band bending only at the spiro‐MeOTAD/perovskite interface of about 0.7 eV. Both the TCS and SDP‐PES show that the perovskite layer is inhomogeneous and has a higher amount of bromine at the perovskite/TiO2 interface.
Open Access
Ultra-uniform perovskite crystals formed in the presence of tetrabutylammonium bistriflimide afford efficient and stable perovskite solar cells
(2024) Lim, Jaekeun; Rafieh, Alwani Imanah; Shibayama, Naoyuki; Xia, Jianxing; Audinot, Jean-Nicolas; Wirtz, Tom; Kinge, Sachin; Glunz, Stefan W.; Ding, Yong; Ding, Bin; Kim, Hobeom; Saliba, Michael; Fei, Zhaofu; Dyson, Paul J.; Nazeeruddin, Mohammad Khaja; Kanda, Hiroyuki
Compositional engineering of organic–inorganic metal halide perovskite allows for improved optoelectrical properties, however, phase segregation occurs during crystal nucleation and limits perovskite solar cell device performance. Herein, we show that by applying tetrabutylammonium bistriflimide as an additive in the perovskite precursor solution, ultra-uniform perovskite crystals are obtained, which effectively increases device performance. As a result, power conversion efficiencies (PCEs) of 24.5% in a cell and 21.2% in a module are achieved, together with high stability under illumination, humidity and elevated thermal conditions.
Open Access
Ultrathin polymeric films for interfacial passivation in wide band-gap perovskite solar cells
(2020) Ferdowsi, Parnian; Ochoa-Martinez, Efrain; Alonso, Sandy Sanchez; Steiner, Ullrich; Saliba, Michael
Wide band-gap perovskite solar cells have the potential for a relatively high output voltage and resilience in a degradation-inducing environment. Investigating the reasons why high voltages with adequate output power have not been realized yet is an underexplored part in perovskite research although it is of paramount interest for multijunction solar cells. One reason is interfacial carrier recombination that leads to reduced carrier lifetimes and voltage loss. To further improve the Voc of methylammonium lead tri-bromide (MAPbBr3), that has a band-gap of 2.3 eV, interface passivation technique is an important strategy. Here we demonstrate two ultrathin passivation layers consisting of PCBM and PMMA, that can effectively passivate defects at the TiO2/perovskite and perovskite/spiro-OMeTAD interfaces, respectively. In addition, perovskite crystallization was investigated with the established anti-solvent method and the novel flash infrared annealing (FIRA) with and without passivation layers. These modifications significantly suppress interfacial recombination providing a pathway for improved VOC’s from 1.27 to 1.41 V using anti solvent and from 1.12 to 1.36 V using FIRA. Furthermore, we obtained more stable devices through passivation after 140 h where the device retained 70% of the initial performance value.
Open Access
Understanding the impact of surface roughness : changing from FTO to ITO to PEN/ITO for flexible perovskite solar cells
(2023) Holzhey, Philippe; Prettl, Michael; Collavini, Silvia; Mortan, Claudiu; Saliba, Michael
So far, single-junction flexible PSCs have been lacking in efficiency compared to rigid PSCs. Recently, > 23% have been reported. We therefore focus on understanding the differences between rigid and flexible substrates. One often neglected parameter is the different surface roughness which directly affects the perovskite film formation. Therefore, we adjust the layer thickness of SnO2 and the perovskite layers. Furthermore, we introduce a PMMA layer between the perovskite and the hole transporting material (HTM), spiro-MeOTAD, to mitigate shunting pathways. In addition, the multication perovskite Rb0.02Cs0.05FA0.77MA0.16Pb(I0.83Br0.17)3 is employed, resulting in stabilized performances of 16% for a flexible ITO substrate and 19% on a rigid ITO substrate.
Open Access
A universal strategy of perovskite ink‐substrate interaction to overcome the poor wettability of a self‐assembled monolayer for reproducible perovskite solar cells
(2023) Kulkarni, Ashish; Sarkar, Ranjini; Akel, Samah; Häser, Maria; Klingebiel, Benjamin; Wuttig, Matthias; Wiegand, Simone; Chakraborty, Sudip; Saliba, Michael; Kirchartz, Thomas
Perovskite solar cells employing [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink-Me-4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF- and DMSO-based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me-4PACz as revealed by density-functional theory calculations. With the optimized triple co-solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm2, respectively. Importantly, this perovskite ink-substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI3, FA1-xMAxPbI3-yBry, and MA-free FA1−xCsxPbI3-yBry.