IISER MOHALI

Abstract: Halide perovskite nanocrystals have emerged as a powerful platform for next-generation self-powered photodetectors, where compositional control and defect engineering can substantially improve optoelectronic performance. In this talk, I will present a unified study of doping and heterojunction engineering across both lead-halide and lead-free double perovskite nanocrystals. In CsPbBr3 nanocrystals, heterovalent Ag⁺/Bi3+ co-doping introduces shallow trap states near the band edges, suppresses Fröhlich electron–phonon coupling, and extends longitudinal optical phonon lifetimes, thereby strengthening the hot-phonon bottleneck and slowing hot-carrier relaxation. These effects lead to a record detectivity of around 8.4 × 1013 Jones and a near-unity photocurrent exponent, indicating highly efficient carrier extraction. I will also discuss charge-transport-layer-free heterojunctions based on Bi-doped CsPbBr3/Cs2AgBiBr6, where type-II band alignment enables bias-free charge separation. Femtosecond transient absorption measurements further reveal ultrafast hot-hole extraction on the order of 270 fs across corrole-based molecular interfaces with CsPbBr3 NCs , resulting in an approximately 180% enhancement in responsivity from the fabricated photodetectors. In the lead-free regime, Cu-doped Cs2AgBiBr6 extends photoresponse into the near-infrared, while Bi-doped Cs2AgInCl6 delivers a UV detectivity of 3.6 × 10¹³ Jones with only 3% degradation after two months of ambient operation. Overall, this work highlights phonon management, defect passivation, and interfacial band engineering as scalable strategies for realizing efficient, stable, and self-powered perovskite optoelectronics. References
1. R. Murali, SSK Raavi et al, J. Phys. Chem. Lett. vol 17, pp. 5872–5879 (2026).
2. C. Barman, SSK Raavi et al, Appl. Phys. Lett. vol. 128, pp 123307 (2026)
3. C. Barman, SSK Raavi et al, J. Mater Chem C. vol. 14, pp. 5922-5933 (2026)
4. C. Barman, SSK Raavi et al, Optics Letters, vol. 12, pp. 4042-4045 (2025)
5. S. K. Nayak, SSK Raavi et al, Small, vol. 21, pp 2410099 (2025)
6. C. Barman, SSK Raavi et al, ACS Appl. Nano Mater. Vol 8, pp 2238-2248 (2025)
7. S. Lavadiya, SSK Raavi et al, ACS Appl. Electron. Mater. vol. 6, 2749–2758 (2024).

About the speaker: Dr. Sai Santosh Kumar Raavi, Full Professor in the Department of Physics at the Indian Institute of Technology Hyderabad, where he is also affiliated faculty with the Department of Climate Change and the Greenko School of Sustainability.

Prof. Raavi's research sits at the intersection of ultrafast optical spectroscopy and nonlinear photonics. His work spans femtosecond transient absorption and photoluminescence spectroscopy of organic and halide perovskite materials, charge photo-generation and transport in solar cells, light-emitting devices and photodetectors, and the nonlinear optical properties of novel molecular and nanocrystal systems.

He earned his Ph.D. in Physics from the University of Hyderabad in 2009, working on nonlinear optics under Prof. Narayana Rao Desai. He went on to complete postdoctoral research at the Politecnico di Milano and the Italian Institute of Technology in Milan, followed by a senior research fellowship at Nanyang Technological University, Singapore. He joined IIT Hyderabad as an Assistant Professor in 2014, rising to Associate Professor in 2018 and Full Professor in 2023.

Prof. Raavi has held several prestigious international research fellowships, including the Bhaskara Advanced Solar Energy (BASE) Fellowship at Princeton University, a FAPESP fellowship at the University of São Paulo in Brazil, a Visiting Researcher position at Japan's National Institute of Materials Science, and — most recently — the JSPS Invitational Fellowship at Kyushu University, Japan.

His contributions have been widely recognized: he is a Fellow of the Royal Society of Chemistry, a Fellow of the Telangana Academy of Sciences, a Senior Member of the Optical Society of America, and a member of the National Academy of Sciences, India. He currently serves as Associate Editor for Elsevier's Optical Materials and sits on the Editorial Advisory Board of APL Engineering Physics.

Over his career, Prof. Raavi has authored more than 140 peer-reviewed journal papers, holds an h-index of 32 with over 4,150 citations, and has been granted multiple patents in device fabrication and photodetector technology. He has mentored numerous graduate students and postdoctoral researchers, and has delivered invited talks at leading international conferences across Asia, Europe, and the Americas.