I started as a postdoctoral researcher at the Max Planck Institute for Polymer Research (MPI-P) Mainz, in September 2020. In the theory group at MPI-P, my research is focused on modeling organic/inorganic hybrid perovskite nanocrystals relevant in electroluminescence applications.
I received my Ph.D. from the University of Minnesota, Twin Cities in Aug. 2020 working in the group of Prof. Christopher J. Cramer. During my graduate studies, I have focused mainly on modeling catalytic processes encompassing both homogeneous and heterogeneous systems. Prior to starting graduate school, I worked with Prof. Debashree Ghosh at the CSIR-National Chemical Laboratory, India, as an intern and explored pathways for UV-induced photo-degradation of eumelanin. I obtained my Master of Science (M.Sc. Chemistry) and Bachelor of Science (B.Sc. Chemistry Honors) degrees from the Indian Institute of Technology (IIT) Bombay, and Ramakrishna Mission Residential College Narendrapur, Kolkata, India, respectively.
Grain Engineering for Improved Charge Carrier Transport in Two-Dimensional Lead-Free Perovskite Field-Effect Transistors
S. Wang, S. Frisch, H. Zhang, O. Yildiz, M. Mandal, N. Ugur, B. Jeong, C. Ramanan, D. Andrienko, H. Wang, M. Bonn, P. W. M. Blom, M. Kivala, W. Pisula, T. Marszalek
Efficient and stable perovskite-silicon tandem solar cells through contact displacement by MgF
J. Liu, M. De Bastiani, E. Aydin, G. T. Harrison, Y. Gao, R. R. Pradhan, M. K. Eswaran, M. Mandal, W. Yan, A. Seitkhan, M. Babics, A. S. Subbiah, E. Ugur, F. Xu, L. Xu, M. Wang, A. ur Rehman, A. Razzaq, J. Kang, R. Azmi, A. A. Said, F. H. Isikgor, T. G. Allen, D. Andrienko, U. Schwingenschloegl, F. Laquai, S. De Wolf
The performance of perovskite solar cells with inverted polarity (p-i-n) is still limited by recombination at their electron extraction interface which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A 1 nm thick MgFx interlayer at the perovskite/C60 interface through thermal evaporation favorably adjusts the surface energy of the perovskite layer facilitating efficient electron extraction and displaces C60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion Voc of 1.92 volts an improved fill factor of 80.7 % and an independently certified stabilized PCE of 29.3 % for a ~1 cm2 monolithic perovskite-silicon tandem solar cell. The tandem retained ~95 % of its initial performance following damp-heat testing (85 Celsius at 85 % relative humidity) for 1000 hours.
Quantum Efficiency Enhancement of Lead-Halide Perovskite Nanocrystal LEDs by Organic Lithium Salt Treatment
T. Naujoks, R. Jayabalan, Ch. Kirsch, F. Zu, M. Mandal, J. Wahl, M. Waibel, A. Opitz, N. Koch, D. Andrienko, M. Scheele, W. Bruetting
ACS Appl. Mater. Interfaces,
Surface-defect passivation is key to achieving a high photoluminescence quantum yield in lead halide perovskite nanocrystals. However in perovskite light-emitting diodes these surface ligands also have to enable balanced charge injection into the nanocrystals to yield high efficiency and operational lifetime. In this respect alkaline halides have been reported to passivate surface trap states and increase the overall stability of perovskite light emitters. On the one side the incorporation of alkaline ions into the lead halide perovskite crystal structure is considered to counterbalance cation vacancies whereas on the other side the excess halides are believed to stabilize the colloids. Here we report an organic lithium salt viz. LiTFSI as a halide-free surface passivation on perovskite nanocrystals. We show that treatment with LiTFSI has multiple beneficial effects on lead halide perovskite nanocrystals and LEDs derived from them. We obtain a higher photoluminescence quantum yield and a longer exciton lifetime and a radiation pattern that is more favorable for light outcoupling. The ligand-induced dipoles on the nanocrystal surface shift their energy levels toward a lower hole-injection barrier. Overall these effects add up to a 4- to 7-fold boost of the external quantum efficiency in proof-of-concept LED structures depending on the color of the used lead halide perovskite nanocrystal emitters.
Improvement of Photophysical Properties of CsPbBr3 and Mn2+:CsPb(BrCl)3 Perovskite Nanocrystals by Sr2+ Doping for White Light-Emitting Diodes
H. Yuce, M. Mandal, Y. Yalcinkaya, D. Andrienko, M. Demir
J. Phys. Chem. C,
All-inorganic metal halide perovskite nanocrystals (NCs) having the general formula ABX3 where A is a monovalent cation for example Cs+ B is a divalent cation typically Pb2+ and X is Cl– Br– I– or their binary mixture show potential in optoelectronic devices. In this work we explore the effect of B-site doping on the optoelectronic properties of CsPbX3 NCs. First the Pb2+ ions in the pristine CsPbBr3 NC are partially substituted by Mn2+ ions. The alkaline earth metal strontium is then doped on both pristine and the Mn2+-substituted NCs. We found that a small percentage of Sr2+ doping remarkably improves the photoluminescence quantum yield of CsPbBr3 and Mn2+-state emission in Mn2+:CsPb(BrCl)3 NCs. Perovskite NC film/poly(methyl methacrylate) composites with all four NC variants were used in a white light-emitting diode (WLED) where Sr2+ doping increased the luminous efficiency of the WLED by ∼4.7%. We attribute this performance enhancement to a reduced defect density and an attenuated microstrain in the local NC structure.
Tuning Interfacial Charge Transfer in Atomically Precise Nanographene-Graphene Heterostructures by Engineering van der Waals Interactions
X. Yu, Sh. Fu, M. Mandal, X. Yao, Zh. Liu, W. Zheng, P. Samorì, A. Narita, K. Muellen, D. Andrienko, M. Bonn, H. Wang
J. Chem. Phys.,
Combining strong light absorption and outstanding electrical conductivity hybrid nanographene-graphene (N-Gr) van der Waals heterostructures (vdWHs) represent an emerging material platform for versatile optoelectronic devices. Interfacial charge transfer (CT) a fundamental process whose full control remains limited plays a paramount role in determining the final device performance. Here we demonstrate that the interlayer vdW interactions can be engineered by tuning the sizes of bottom-up synthesized NGs to control the interfacial electronic coupling strength and thus the CT process in NG-Gr vdWHs. By increasing the dimensions of NGs from 42 to 96 sp2 carbon atoms in the polyaromatic core to enhance the interfacial coupling strength we find that the CT efficiency and rate in NG-Gr vdWHs display a drastic increase of one order of magnitude despite the fact that the interfacial energy driving the CT process is unfavorably reduced. Our results shed light on the CT mechanism and provide an effective knob to tune the electronic coupling at NG-Gr interfaces by controlling the size-dependent vdW interactions.
Spatially resolved fluorescence of caesium lead halide perovskite supercrystals reveals quasi-atomic behavior of nanocrystals
D. Lapkin, C. Kirsch, J. Hiller, D. Andrienko, D. Assalauova, K. Braun, J. Carnis, Y. Y. Kim, M. Mandal, A. Maier, A. J. Meixner, N. Mukharamova, M. Scheele, F. Schreiber, M. Sprung, J. Wahl, S. Westendorf, I. A. Zaluzhnyy, I. A. Vartanyants
Porphyrin-functionalization of CsPbBrI2/SiO2 core-shell nanocrystals enhances the stability and efficiency in electroluminescent devices
J. Wahl, M. Engelmayer, M. Mandal, T. Naujoks, P. Haizmann, A. Maier, H. Peisert, D. Andrienko, W. Bruetting, M. Scheele
Adv. Optical Mater.,
Surface ligand exchange on all-inorganic perovskite nanocrystals of composition CsPbBrI2 reveals improved optoelectronic properties due to strong interactions of the nanocrystal with mono-functionalized porphyrin derivatives. The interaction is verified experimentally with an array of spectroscopic measurements as well as computationally by exploiting density functional theory calculations. The enhanced current efficiency is attributed to a lowering of the charging energy by a factor of 2-3 which is determined by combining electronic and optical measurements on a selection of ligands. The coupled organic–inorganic nanostructures are successfully deployed in a light-emitting device with higher current efficacy and improved charge carrier balance magnifying the efficiency almost fivefold compared to the native ligand.