TY - GEN A1 - Das, Chittaranjan A1 - Kedia, Mayank A1 - Zuo, Weiwei A1 - Mortan, Claudiu A1 - Kot, Małgorzata A1 - Flege, Jan Ingo A1 - Saliba, Michael T1 - Band Bending at Hole Transporting Layer-Perovskite Interfaces in n-i-p and in p-i-n Architecture T2 - Solar RRL N2 - Interfaces between hybrid perovskite absorber and its adjacent charge-transporting layers are of high importance for solar cells performance. Understanding their chemical and electronic properties is a key step in designing efficient and stable perovskite solar cells. In this work, the tapered cross-section photoemission spectroscopy (TCS-PES) method is used to study the methylammonium lead iodide (CH3NH3PbI3) (MAPI)-based solar cells in two configurations, that is, in an inverted p–i–n and in a classical n–i–p architecture. It is revealed in the results that the MAPI film deposited once on the n-type TiO2 and once on the p-type NiOx substrates is neither an intrinsic semiconductor nor adapts to the dopant nature of the substrate underneath, but it is heavily n-type doped on both substrates. In addition to that, the TCS-PES results identify that the band bending between the MAPI film and the hole transporting layer (HTL) layer depends on the perovskite solar cells architecture. In particular, a band bending on the HTL side in the n–i–p and at the MAPI in the p–i–n architecture is found. The flat band of NiOx at the NiOx/MAPI interface can be explained by the Fermi level pinning of the NiOx at the interface. KW - band bending KW - hole transporting layer KW - perovskites KW - X-ray photoelectron spectroscopy (XPS) Y1 - 2022 U6 - https://doi.org/10.1002/solr.202200348 SN - 2367-198X VL - 6 IS - 9 ER - TY - GEN A1 - Zia, Waqas A1 - Malekshahi Byranvand, Mahdi A1 - Rudolph, Toby A1 - Rai, Monika A1 - Kot, Małgorzata A1 - Das, Chittaranjan A1 - Kedia, Mayank A1 - Zohdi, Mohammadreza A1 - Zuo, Weiwei A1 - Yeddu, Vishal A1 - Saidaminov, Makhsud I. A1 - Flege, Jan Ingo A1 - Kirchartz, Thomas A1 - Saliba, Michael T1 - MAPbCl3 Light Absorber for Highest Voltage Perovskite Solar Cells T2 - ACS Energy Letters N2 - Perovskite solar cells (PSCs) excel in achieving high open-circuit voltages (VOC) for narrow bandgaps (∼1.6 eV) but face challenges with wide-bandgap perovskites, like methylammonium lead trichloride (MAPbCl3) with a 3.03 eV bandgap. These materials are transparent in visible absorbing ultraviolet (UV) light. However, achieving uniform film crystallization remains a hurdle. Here, we enhance MAPbCl3 crystallization by manipulating annealing atmospheres (nitrogen, air, and MACl vapor). Excess MACl vapor improves surface coverage, which is crucial for film stability. We demonstrate that the microstructure of the perovskite film, including surface morphology, grain boundaries, and interfaces, can affect the photovoltaic properties. The subsequently obtained VOC of 1.78 V is the highest recorded for single-junction PSCs to the best of our knowledge. Surprisingly, the conventional hole-transport layer spiro-OMeTAD, optimized for narrow bandgaps, sustains such high voltages. Photoluminescence measurements reveal a trap-assisted recombination peak at 1.65 eV, indicating deep traps as significant to voltage loss in MAPbCl3. KW - Perovskite solar cells KW - methylammonium lead trichloride (MAPbCl3) KW - uniform film crystallization KW - manipulation of annealing atmospheres KW - trap-assisted recombination KW - microstructure Y1 - 2024 U6 - https://doi.org/10.1021/acsenergylett.3c02777 SN - 2380-8195 VL - 9 SP - 1017 EP - 1024 ER - TY - GEN A1 - Zuo, Weiwei A1 - Malekshahi Byranvand, Mahdi A1 - Kodalle, Tim A1 - Zohdi, Mohammadreza A1 - Lim, Jaekeun A1 - Carlsen, Brian A1 - Friedlmeier, Theresa Magorian A1 - Kot, Małgorzata A1 - Das, Chittaranjan A1 - Flege, Jan Ingo A1 - Zong, Wansheng A1 - Abate, Antonio A1 - Sutter‐Fella, Carolin M. A1 - Li, Meng A1 - Saliba, Michael T1 - Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization T2 - Advanced Materials N2 - 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. KW - Perovskite solar cells KW - nucleation KW - dimethyl sulfide ()DMS) solvent KW - coordination chemistry Y1 - 2023 U6 - https://doi.org/10.1002/adma.202302889 SN - 0935-9648 SN - 1521-4095 VL - 35 IS - 39 ER - TY - GEN A1 - Das, Chittaranjan A1 - Roy, Rajarshi A1 - Kedia, Mayank A1 - Kot, Małgorzata A1 - Zuo, Weiwei A1 - Félix, Roberto A1 - Sobol, Tomasz A1 - Flege, Jan Ingo A1 - Saliba, Michael T1 - Unraveling the Role of Perovskite in Buried Interface Passivation T2 - ACS Applied Materials & Interfaces N2 - Interfaces in perovskite solar cells play a crucial role in their overall performance, and therefore, detailed fundamental studies are needed for a better understanding. In the case of the classical n–i–p architecture, TiO2 is one of the most used electron-selective layers and can induce chemical reactions that influence the performance of the overall device stack. The interfacial properties at the TiO2/perovskite interface are often neglected, owing to the difficulty in accessing this interface. Here, we use X-rays of variable energies to study the interface of (compact and mesoporous) TiO2/perovskite in such a n–i–p architecture. The X-ray photoelectron spectroscopy and X-ray absorption spectroscopy methods show that the defect states present in the TiO2 layer are passivated by a chemical interaction of the perovskite precursor solution during the formation of the perovskite layer and form an organic layer at the interface. Such passivation of intrinsic defects in TiO2 removes charge recombination centers and shifts the bands upward. Therefore, interface defect passivation by oxidation of Ti3+ states, the organic cation layer, and an upward band bending at the TiO2/perovskite interface explain the origin of an improved electron extraction and hole-blocking nature of TiO2 in the n–i–p perovskite solar cells. KW - perovskite solar cells KW - interface KW - defects KW - photoemission spectroscopy Y1 - 2023 U6 - https://doi.org/10.1021/acsami.3c13085 SN - 1944-8244 SN - 1944-8252 VL - 15 IS - 48 SP - 56500 EP - 56510 ER - TY - GEN A1 - Kedia, Mayank A1 - Das, Chittaranjan A1 - Kot, Malgorzata A1 - Yalcinkaya, Yenal A1 - Zuo, Weiwei A1 - Tabah Tanko, Kenedy A1 - Matvija, Peter A1 - Ezquer, Mikel A1 - Cornago, Iñaki A1 - Hempel, Wolfram A1 - Kauffmann, Florian A1 - Plate, Paul A1 - Lira-Cantu, Monica A1 - Weber, Stefan A.L. A1 - Saliba, Michael T1 - Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina T2 - Energy & environmental science N2 - 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. Y1 - 2025 U6 - https://doi.org/10.1039/D4EE05703A SN - 1754-5692 VL - 18 IS - 11 SP - 5250 EP - 5263 PB - Royal Society of Chemistry (RSC) CY - London ER -