Photo-Iontronics (π)

Exploring π-powered devices: where light, ions, and electrons meet

Dr. Ramesh Kumar

Alexander von Humboldt Research Fellow, Institute for Microsensors, Actuators and Systems, Uni-Bremen, Germany

& Visiting Postdoctoral Researcher at Ångström Laboratory, Uppsala University, Sweden

About me

I am currently an Alexander von Humboldt Research Fellow (2024–2026) at the Institut für Mikrosensoren, -aktoren und -systeme, University of Bremen, Germany. My research is focused on decoding ion dynamics in organic electrochemical transistors (OECTs)—a cutting-edge field bridging organic electronics and electrochemistry.

Previously, I held a postdoctoral position at Uppsala University, Sweden, in the Boschloo-Johansson group, where I worked on lead-free, perovskite-inspired materials for solar energy applications. My broader expertise lies in the design, fabrication, and fundamental characterization of perovskite-based optoelectronic and photovoltaic devices, as well as electrochemical electronic systems, including photo-supercapacitors and OECTs.

I employ small-perturbation frequency and time-domain techniques—such as Electrochemical Impedance Spectroscopy (EIS), Intensity Modulated Photocurrent/Voltage Spectroscopy (IMPS/IMVS), and Transient Photovoltage/Photocurrent (TPV/TPC)—to probe device physics and unravel performance-limiting factors.

To date, I have published 25+ peer-reviewed articles, authored three book chapters, secured one patent, and presented my work at numerous international conferences.

My academic journey includes higher education from premier Indian institutions, including Delhi University, NIT Jaipur, and IIT Roorkee. I have qualified several national-level competitive examinations, such as GATE (2016–2018) with a top rank of 500 and the CSIR-NET, securing an All India Rank of 100.

Honors and Fellowships

Young investigator group preparation grant, Karlsruhe Institute of Technology (KIT), Germany.
Alexander von Humboldt Research Fellowship, AvH Foundation, Germany (2024–2026).
Swedish Postdoctoral Fellowship, Olle Engkvist Foundation, Sweden (2023–2025).
Commonwealth Scholarship, UK Government (2021–2022).
PhD Scholarship, Government of India (2017-2022)
Travel Grants, IIT Roorkee 2020.

Latest Research articles

The promise of operational stability in pnictogen-based perovskite-inspired solar cells

EES Solar 1 (2), 139-156

Perovskite-inspired materials (PIMs) are gaining increasing attention among emerging photovoltaic absorbers due to their inherent air stability and low-toxicity potential. However, operational stability, the Achilles' heel of all emerging photovoltaics, has been largely overlooked in PIMs research so far, making it difficult to forecast their practical use in real-world applications. In this work, we analyse the operational stability of a promising new PIM composition, CsMAFA-Sb:Bi, generated through the antimony:bismuth co-alloying of a triple cation vacancy-ordered antimony-based PIM. Through an in-depth theoretical and experimental investigation, we demonstrate that the co-alloying induces local structural changes that lead to enhanced microstructure, reduced trap-assisted recombination, and increased solar cell power conversion efficiency (PCE), with the highest value being 3.05%. Accelerated aging tests according to ISOS L-1 and L-2 protocols highlight the crucial role of co-alloying in enhancing stability. Specifically, maximum power point tracking at 85 °C shows a projected T80 lifetime of 275 hours for CsMAFA-Sb:Bi devices, which has never been achieved not only for any other PIM-based device but also for high-efficiency technologies, such as lead halide perovskite solar cells with similar device constituents. This work encourages future studies on PIM-based photovoltaics for their potential operational stability, with the goal of reducing the performance gap with established technologies.

Electrolyte-Gated Ruddlesden–Popper Perovskites for Switchable Optoelectronic Universal Logic Gates

Electrolyte-gated semiconductor devices are the building blocks for next-generation optoelectronics due to their memory effect and slow ion kinetics, mimicking synapses. Halide perovskites have memory effects, mixed electronic and ionic conductivity, and optical responses, which are extremely promising for this application. However, most high-performance halide perovskites are unstable in liquid electrolytes due to solvent intercalation. We have stabilized the Ruddlesden–Popper 2D perovskites by introducing an ion-transporting membrane separator between the thin film and a quasi-solid-state gel electrolyte interface. Here, we demonstrate an electrolyte-gated three-terminal device that operates as a switchable OR, AND, and a universal NOR gate, with one input being electrical and the other being optical, based on negative, zero, and positive gate voltages, respectively.

Nano Lett. 2025, 25, 12, 4961–4968

Developing versatile absorbers for indoor photovoltaics (IPVs) to adapt to various lighting conditions in different indoor environments is crucial for advancing IPVs. In this work, we present Cs2AgBi2I9, a new absorber with unique optoelectronic properties compared to other bismuth-based perovskite-inspired materials. Cs2AgBi2I9-based IPVs display high performance under various LED light colours, from warm to cold white.