Photovoltaic-Electrochemical Devices


Intermittent power generation is one of the major issues for practical applications of photovoltaics (PV). Electrochemical devices like batteries and electrolyzers offer various ways to store and utilize excess PV energy which can significantly improve the stability of PV electricity supply. We focus on direct electrical coupling and integration of PV devices with batteries, and electrolyzers converting carbon dioxide (CO2), water, and sunlight into valuable chemical products.

Research Topics

Coupling and integration of photovoltaics with batteries.
Artificial leaf devices for PV-driven conversion of CO2.
Directly coupled PV-electrochemical devices.
Combined photovoltaic-battery-electrolyzer devices.
Potential and practical aspects of green energy transition in Africa.


Dr. Tsvetelina Merdzhanova


Building 02.6 / Room 4005

+49 2461/61-3177


Publications of the group

Coupling and integration of photovoltaics with batteries

Photovoltaic-Electrochemical Devices

We follow a simple, scalable, and highly efficient concept of direct coupling of PV cells and modules to batteries. Optimal operation of the PV-battery device is facilitated via proper preselection of components. This contrasts with the well-established concept of using maximum power point tracker electronics. We demonstrated excellent power matching of a directly coupled PV-battery system under realistic cycling. The development is directed to larger-scale devices, long-term stability, and integration into novel PV system architectures.

Photovoltaisch-elektrochemische Bauelemente

Integration of photovoltaic devices with rechargeable batteries is a promising solution for internet-of-things devices and sensors operating indoors. Modern LED lighting matches well with perovskite solar cells. We demonstrate exceptionally high efficiency in LED energy harvesting and storage with perovskite modules directly coupled to sodium-ion batteries without power electronics (overall PV-battery efficiency of 26.4%). We continue to develop scalable self-sustained power solutions for small-scale indoor electronics.

S. Shcherbachenko et al. Efficient Power Coupling in Directly Connected Photovoltaic‐Battery Module
Solar RRL 2367-198X, 2200857 (2023)

U. Chibuko et al. Module-level direct coupling in PV-battery power unit under realistic irradiance and load
Solar energy 249, 233 - 241 (2023)

L.-C. Kin et al. Efficient indoor light harvesting with CH3NH3Pb(I0.8Br0.2)3 solar modules and sodium-ion battery
Cell reports 3 (11) 101123 (2022)

N. Hamzelui et al. Toward the integration of a silicon/graphite-anode based lithium-ion battery in photovoltaic charging battery systems
ACS omega 7, 27532 (2022)

O. Astakhov et al. From room to roof: How feasible is direct coupling of solar-battery power unit under variable irradiance?
Solar energy 206, 732 - 740 (2020)

L.-C. Kin et al. Efficient Area Matched Converter Aided Solar Charging of Lithium Ion Batteries Using High Voltage Perovskite Solar Cells
ACS applied energy materials 3(1), 431 - 439 (2020)

F. Sandbaumhüter et al. Compatibility study towards monolithic self-charging power unit based on all-solid thin-film solar module and battery
Journal of Power Sources 365, 303 (2017)

S. N. Agbo et al. Illumination intensity and spectrum-dependent performance of thin-film silicon single and multijunction solar cells
Solar Energy Materials and Solar Cells 159, 427 (2017)

S. N. Agbo et al. Development towards cell-to cell monolithic integration of a thin-film solar cell and lithium-ion accumulator
Journal of Power Sources 327, 340 (2016)

Artificial leaf devices for PV-driven conversion of CO2

Photovoltaisch-elektrochemische Bauelemente

Long-term storage in molecules like fuels or other industrially useful chemicals is most relevant for counterbalancing natural yearly oscillations in photovoltaic power generation. We address this challenge via ‘artificial leaf’ approach – conversion of carbon dioxide (CO2), water (H2O) and sunlight into valuable chemical products with a direct photovoltaic-driven electrolysis (PV-EC). The PV-EC approach in direct connection is attractive as a good compromise between the design flexibility and high solar to fuel efficiencies. Various combinations of PV and EC devices are addressed with emphasis on critical raw materials free technologies. Performance of the directly coupled systems is studied in the context of realistic variations of the PV irradiance and temperature. We conduct the research using inhouse facilities for preparation of photovoltaic and electrochemical components, as well as participating international projects like H2020 projects A-leaf and DECADE. Resent achievement of over 6 % solar-to-fuel efficiency, the record value for a device without critical raw materials is further developed in the European project SUPERVAL with focus on CO2 valorization.

C. Ampelli et al. An artificial leaf device built with earth-abundant materials for combined H2 production and storage as formate with efficiency > 10%
Energy Environ. Sci., 16, 1644-1661 (2023)

F. LP Veenstra et al. CO2 electroreduction to syngas with tunable composition in an artificial leaf
ChemSusChem2023, e202301398

CO2 conversion Projects

SUPERVAL - design and realize an autonomous, solar-powered installation able to capture harmful emissions from flue gas, and valorize them as commodities for the chemical industry

A-LEAF (Horizon 2020 under Grant agreement no: 732840) realization of artificial photosynthesis to capture and transform solar energy into chemical energy, as a sustainable substitute for fossil resources

DECADE (Horizon 2020 Project under Grant agreement no: 862030)
Distributed chemicals and fuels production from CO2 in photoelectrocatalytic devices

A-LEAF (Horizon 2020 under Grant agreement no: 732840) realization of artificial photosynthesis to capture and transform solar energy into chemical energy, as a sustainable substitute for fossil resources

DECADE (Horizon 2020 Project under Grant agreement no: 862030)
Distributed chemicals and fuels production from CO2 in photoelectrocatalytic devices

Directly coupled PV-electrochemical devices for water splitting

Photovoltaic-Electrochemical Devices

Hydrogen production via water electrolysis is one of the simplest routes for the long-term storage of PV energy. We develop directly coupled PV-electrochemical combinations (PV-EC systems) aiming at the simplest and material-saving yet highly efficient solutions utilizing earth-abundant materials. We experiment with different PV technologies including Si and Perovskite as well as different water-splitting electrolyzers. We develop methods to predict the peak and long-term performance of these systems in lab and field conditions. Ongoing research is focused on the upscaling, real field performance, and long-term stability of the PV-EC systems.

O. Astakhov et al. Prediction of Limits of Solar‐to‐Hydrogen Efficiency from Polarization Curves of the Electrochemical Cells
Solar RRL 6(2), 2100783 (2022)

D. Cardenas-Morcoso et al. An integrated photoanode based on non-critical raw materials for robust solar water splitting
Materials Advances 1(5), 1202-1211 (2020

M. Lee et al. Bifunctional CoFeVOx Catalyst for Solar Water Splitting by using Multijunction and Heterojunction Silicon Solar Cells
Advanced materials technologies 5(12), 2000592 (2020)

Combined photovoltaic-battery-electrolyzer devices

Photovoltaisch-elektrochemische Bauelemente

PV requires short- and long-term energy storage to counteract daily and seasonal power variations. We address both storage timescales simultaneously with the directly coupled photovoltaic-electrolyzer-battery combinations (PV-EC-B for short). We have demonstrated theoretically and experimentally the functionality of the PV-EC-B system without any power electronics. The battery provides stable power coupling and uninterrupted 24h operation which operates now at higher efficiency. The gain in solar-to-hydrogen efficiency is experimentally confirmed. Currently, we focus on the long time performance of the directly coupled PV-EC-B systems.

L.-C. Kin et al. Batteries to Keep Solar‐Driven Water Splitting Running at Night: Performance of a Directly Coupled System
Solar RRL 6(4), 2100916 (2022)

O. Astakhov et al. Storage batteries in photovoltaic–electrochemical device for solar hydrogen production
Journal of power sources 509, 230367 (2021)

Thin silicon heterojunction solar cells and modules

Photovoltaisch-elektrochemische Bauelemente

In collaboration with Silicon Heterojunction Solar Cells and Modules group we develop custom cells and modules based on the Si heterojunction (SHJ) technology to couple with electrochemical devices of lab scale and beyond.
A feasible course for improvement in terms of energy return on investment is the transition towards thinner wafers. Solar cells made from thinner wafers have a few advantages: material and cost savings, improved flexibility, and reduced carbon footprint in the production process. We study here the wafer thickness effect of silicon heterojunction solar cells on solar cell parameters. Interesting results show the increase in open circuit voltage for thinner wafers with implied values approaching the theoretical limit. Overall, final results show a broad range of high efficiencies between 75 and 170 µm. We also study the optimization and application of thin wafer-based cells and modules as bottom cells in tandems and for power coupling in electrochemical devices respectively.

U. Chime et al. How Thin Practical Silicon Heterojunction Solar Cells Could Be? Experimental Study under 1 Sun and under Indoor Illumination
Solar RRL 6(1), 2100594 (2022)

Projects on green energy transition in Africa

Photovoltaic-Electrochemical Devices

YESPV-NIGBEN (BMBF Förderkennzeichen 03SF0576A-B
Promotion of an integrated Agri-PV greenhouse concept to ensure food, energy, and jobs for local African communities with smart and efficient land use methods. The concept for generating sustainable energy avoiding land use conflict with food production. Five integrated PV systems have been built at the University of Nigeria Nsukka for food and energy production, and electricity for hospital and educational buildings.

H2-Atlas Africa
Assessing the potential of generating hydrogen in sub-Saharan Africa from renewable energy resources. Evaluation of the potentials of volatile renewable energy sources. We verify the PV performance model implemented with focus on the spectral effects of irradiance in Africa

PV2H-BURKINA (Optimizing Solar PV for Green Hydrogen Production in West Africa)
In this project we aim at a technical solution to the negative impact of soiling on solar PV power plants and propose ways to optimize the PV production from solar PV systems under the specific climatic conditions of the Sahelian region in West Africa

Group members

Last Modified: 22.11.2023