Tanaji P. Gujar
University of Bayreuth
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Featured researches published by Tanaji P. Gujar.
APL Materials | 2016
Eugen Zimmermann; Ka Kan Wong; Michael Müller; Hao Hu; Philipp Ehrenreich; Markus Kohlstädt; Uli Würfel; Simone Mastroianni; Gayathri Mathiazhagan; Andreas Hinsch; Tanaji P. Gujar; Mukundan Thelakkat; Thomas Pfadler; Lukas Schmidt-Mende
Lead halide perovskite solar cells have shown a tremendous rise in power conversion efficiency with reported record efficiencies of over 20% making this material very promising as a low cost alternative to conventional inorganic solar cells. However, due to a differently severe “hysteretic” behaviour during current density-voltage measurements, which strongly depends on scan rate, device and measurement history, preparation method, device architecture, etc., commonly used solar cell measurements do not give reliable or even reproducible results. For the aspect of commercialization and the possibility to compare results of different devices among different laboratories, it is necessary to establish a measurement protocol which gives reproducible results. Therefore, we compare device characteristics derived from standard current density-voltage measurements with stabilized values obtained from an adaptive tracking of the maximum power point and the open circuit voltage as well as characteristics extracted from time resolved current density-voltage measurements. Our results provide insight into the challenges of a correct determination of device performance and propose a measurement protocol for a reliable characterisation which is easy to implement and has been tested on varying perovskite solar cells fabricated in different laboratories.
Journal of Physical Chemistry Letters | 2016
Shivam Singh; Cheng Li; Fabian Panzer; K. L. Narasimhan; Anna Graeser; Tanaji P. Gujar; Anna Köhler; Mukundan Thelakkat; Sven Huettner; Dinesh Kabra
In this Letter, we investigate the temperature dependence of the optical properties of methylammonium lead iodide (MAPbI3 = CH3NH3PbI3) from room temperature to 6 K. In both the tetragonal (T > 163 K) and the orthorhombic (T < 163 K) phases of MAPbI3, the band gap (from both absorption and photoluminescence (PL) measurements) decreases with decrease in temperature, in contrast to what is normally seen for many inorganic semiconductors, such as Si, GaAs, GaN, etc. We show that in the perovskites reported here, the temperature coefficient of thermal expansion is large and accounts for the positive temperature coefficient of the band gap. A detailed analysis of the exciton line width allows us to distinguish between static and dynamic disorder. The low-energy tail of the exciton absorption is reminiscent of Urbach absorption. The Urbach energy is a measure of the disorder, which is modeled using thermal and static disorder for both the phases separately. The static disorder component, manifested in the exciton line width at low temperature, is small. Above 60 K, thermal disorder increases the line width. Both these features are a measure of the high crystal quality and low disorder of the perovskite films even though they are produced from solution.
Materials | 2016
Fabian Panzer; Tanaji P. Gujar; Frank-Julian Kahle; Mukundan Thelakkat; Anna Köhler; Ralf Moos
We present the successful fabrication of CH3NH3PbI3 perovskite layers by the aerosol deposition method (ADM). The layers show high structural purity and compactness, thus making them suitable for application in perovskite-based optoelectronic devices. By using the aerosol deposition method we are able to decouple material synthesis from layer processing. Our results therefore allow for enhanced and easy control over the fabrication of perovskite-based devices, further paving the way for their commercialization.
Journal of Materials Chemistry C | 2018
Tobias Meier; Tanaji P. Gujar; Andreas Schönleber; Selina Olthof; Klaus Meerholz; Sander van Smaalen; Fabian Panzer; Mukundan Thelakkat; Anna Köhler
We investigate the impact of excess PbI2 in the precursor solution on the structural and optical properties of thin films of the model hybrid perovskite methylammonium lead iodide (MAPbI3). We find that excess of PbI2 in the precursor solution results in crystalline PbI2 in the final thin film that is located at the grain boundaries. From UPS we find that this crystalline PbI2 phase has no direct impact on the electronic structure of MAPbI3. In contrast to this, temperature dependent absorption measurements indicate a systematic change in the temperature dependence of the exciton binding energy in the perovskite. We also observe a decrease in the critical temperature and a concomitant smearing out of the tetragonal–orthorhombic phase transition as a function of excess PbI2. Our results thus help to better understand the exact role of PbI2 in the perovskite layer and pave the way for a more tailored design of perovskite solar cells.
Advanced Energy Materials | 2017
Michiel L. Petrus; Johannes Schlipf; Cheng Li; Tanaji P. Gujar; Nadja Giesbrecht; Peter Müller-Buschbaum; Mukundan Thelakkat; Thomas Bein; Sven Hüttner; Pablo Docampo
Advanced Optical Materials | 2016
Fabian Panzer; Sebastian Baderschneider; Tanaji P. Gujar; Thomas Unger; Sergey A. Bagnich; Marius Jakoby; H. Bässler; Sven Hüttner; Jürgen Köhler; Ralf Moos; Mukundan Thelakkat; Richard Hildner; Anna Köhler
Energy technology | 2016
Tanaji P. Gujar; Mukundan Thelakkat
Physical Chemistry Chemical Physics | 2018
Tanaji P. Gujar; Thomas Unger; Andreas Schönleber; Martina Fried; Fabian Panzer; Sander van Smaalen; Anna Köhler; Mukundan Thelakkat
Physical Chemistry Chemical Physics | 2016
Chetan R. Singh; Tobias Honold; Tanaji P. Gujar; Markus Retsch; Andreas Fery; Matthias Karg; Mukundan Thelakkat
Advanced Energy Materials | 2017
Michiel L. Petrus; Johannes Schlipf; Cheng Li; Tanaji P. Gujar; Nadja Giesbrecht; Peter Müller-Buschbaum; Mukundan Thelakkat; Thomas Bein; Sven Hüttner; Pablo Docampo