Batteries go solar – Project SolBat funded by the Max Planck Foundation with around 3 Mio. Euros

February 09, 2024

Joint project between the Max Planck Institute for Solid State Research (Stuttgart) and the Fritz Haber Institute of the Max Planck Society (Berlin) explores new avenues to solar batteries and other optoionic technologies.


Our Society is facing unprecedented challenges in the areas of energy and sustainability. In order to develop innovative renewable energy solutions for the “Energy Transition 2.0”, modern materials are as important as new concepts for energy conversion and storage.

Renewable energy is the backbone of the energy transition: The world's available solar energy exceeds the global energy demand many times over. At the same time, its fluctuating availability poses enormous challenges when it comes to stabilizing the electricity grid. Bridging technologies that can convert and store energy in a flexible way to compensate for the intermittent nature of wind and solar power are therefore crucial. In particular, "solar buffers" are required to compensate not only for seasonal (summer-winter) and diurnal (day-night) fluctuations, but also for short-term weather-related variations on a time scale of hours and minutes.

The SolBat project aims to develop new types of "light storage devices" that combine solar cells and batteries in a single component. Such solar batteries can either be charged with light, or light can help accelerate the electrical charging process. Solar batteries could thus act as a "solar buffer", temporarily storing sunlight to compensate for the fluctuating availability of solar energy.

The foundations of solar batteries are defined by the emerging research field of optoionics, which lies at the intersection of optoelectronics and solid state ionics and has been conceptualized at the Max-Planck Institute for Solid State Research [1-3]. Optoionics is the study of interaction of light with ions in solids, such as the lithium ions in lithium-ion batteries. The potential of this uncharted scientific territory is enormous: The ability of controlling ions with light opens up prospects for novel optoionic technologies at the intersection between photovoltaics, photocatalysis and electrochemical energy storage – from the delayed production of solar fuels such as hydrogen in the dark ("dark photocatalysis") [4] to light-driven sensors or neuromorphic data storage [5, 6].

The SolBat initiative, led by Professor Bettina V. Lotsch, Max Planck Institute for Solid State Research, Stuttgart (MPI-FKF) and Professor Karsten Reuter, Fritz Haber Institute of the Max Planck Society, Berlin (FHI-MPG), aims to advance the fundamental understanding of optoionic materials and processes, as well as  to develop new application areas for optoionic processes. The project dives into two exciting areas: one explores cutting-edge and scalable energy technologies, while the other focuses on management of miniaturized microsystem for the “Internet of Things” or data processing.

The realisation of such processes largely depends on the availability of optoionic materials. In order to accelerate the discovery of such materials and thus advance optoionic technologies, a concerted approach of experiments and theory is essential. Therefore, the experimental Nanochemistry Department (Bettina V. Lotsch) and the Theory Department at the FHI-MPG (Karsten Reuter) are working hand in hand within SolBat to integrate data-based material prediction, AI-based evaluation methods and robotic material synthesis in a tight feedback loop to drive forward the innovative, translational components of the project.

By combining fundamental research and innovative applications, the SolBat initiative is performing pioneering work at the interface between energy conversion and storage to develop new solutions for the substantially increased energy storage requirements of the future.




[1]  G. Y. Kim, A. Senocrate, T.-Y. Yang, G. Gregori, M. Grätzel, J. Maier, Nature Materials 2018, 17, 445–449.

Large tunable photoeffect on ion conduction in halide perovskites and implications for photodecomposition

[2]  A. Senocrate, E. Kotomin, J. Maier, Helvetica chimica acta 2020, 103, e2000073.

On the Way to Optoionics

[3]  F. Podjaski, B. V. Lotsch, Advanced Energy Materials 2021, 11, 2003049.

Optoelectronics Meets Optoionics: Light Storing Carbon Nitrides and Beyond

[4]  V. W.-h. Lau, D. Klose, H. Kasap, F. Podjaski, M.-C. Pignié, E. Reisner, G. Jeschke, B. V. Lotsch, Angewandte Chemie – International Edition 2017, 56, 510–514.

Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time-Delayed Hydrogen Generation

[5]  A. Gouder, A. Jiménez-Solano, N. M. Vargas-Barbosa, F. Podjaski, B. V. Lotsch, Materials Horizons 2022, 9, 1866–1877.

Photomemristive sensing via charge storage in 2D carbon nitrides

[6]  A. Gouder, F. Podjaski, A. Jiménez-Solano, J. Kröger, Y. Wang, B. V. Lotsch, Energy & Environmental Science 2023, 16, 1520–1530.

An integrated solar battery based on a charge storing 2D carbon nitride



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