Photovoltaics Nanophysics Light-Matter Interaction
PI: Prof. Dr. Rebecca Saive (https://people.utwente.nl/r.saive)
Overview
The Saive research group develops new concepts and enabling technologies for next-generation light-energy conversion. Our research is centered on solar energy conversion, photonic and optical metamaterials, advanced microfabrication, and in-operando scanning probe microscopy. We are particularly interested in how light–matter interaction can be engineered to unlock new functionality in photovoltaic and optoelectronic systems.
Our work combines fundamental experimental physics with technology development. We investigate physical mechanisms in order to create innovative solutions and we pursue research lines until either a robust technological concept emerges or fundamental limitations become clear. In this way, the group bridges basic science, device physics, manufacturing, and valorization.
The group currently works along three main research directions:
- photonic metamaterials and optical concepts for enhanced solar-energy yield,
- advanced front-contact architectures and scalable fabrication for photovoltaics,
- in-operando microscopy of charge transport and interfaces in functioning optoelectronic devices.
Solar energy
Solar energy is the largest accessible energy resource on Earth and will play a central role in a sustainable, resilient, and affordable energy system. While the cost of solar electricity has decreased dramatically, further progress requires not only continued improvements in photovoltaic materials and devices, but also new concepts that address yield, scalability, manufacturability, critical materials reduction, and system integration.
Our group contributes to this transition by developing new approaches to solar-energy conversion that combine scientific originality with technological relevance. We focus not only on improving solar cells themselves, but also on the optical environment, interfaces, and manufacturing strategies that determine performance in real-world conditions.
Photonic materials and optical concepts for solar-energy conversion
A major focus of the group is the development of optical strategies that improve photovoltaic performance beyond conventional device optimization. Instead of only optimizing absorber materials, we explore how the optical surroundings of solar cells and modules can be engineered to increase energy yield.
This includes research on:
- free-space diffuse-light collimation,
- optical metamaterials for enhanced solar energy yield,
- albedo engineering and yield modeling,
- albedo and light sharing in agriphotovoltaics,
Our work has demonstrated record-level free-space diffuse-light collimation and has shown how spectral conversion and angular redistribution can be used to increase photovoltaic yield, especially under realistic and diffuse illumination conditions. A particular motivation is to enhance winter electricity generation and thereby help reduce the seasonal mismatch between solar supply and energy demand.
Figure credit: Mathis Van de Voorde
Key publications include:
Einhaus, Lisanne M, Heres, Geert C, Westerhof, Jelle, Pal, Shweta, Kumar, Akshay, Zheng, Jian-Yao & Saive, Rebecca. Free-space diffused light collimation and concentration. ACS photonics, 10(2), 508-517 (2023).
Advanced front contacts and scalable fabrication for photovoltaics
Our second research line addresses one of the most persistent challenges in photovoltaics: the trade-off between optical transparency and electrical conductivity at the front side of solar cells. Metallic front contacts are essential for charge collection, but they also reflect and block incoming light.
During her postdoctoral work at Caltech, Rebecca Saive developed effectively transparent contacts (ETCs), a front-contact concept based on triangular microscale metallic structures that redirect light into the absorber instead of reflecting it away. This work led to several patents, multiple awards and recognitions, and the development of the Microchannel Particle Deposition manufacturing method. It also formed the basis of the spin-off company ETC Solar, now MESOLINE, which was successfully exited in 2021.
At the University of Twente, the group has further advanced this line of research by developing string printing, a new and more scalable fabrication route for high-aspect-ratio front contacts tailored to the needs of solar manufacturing. We study both the optical and electrical properties of these contact architectures and their integration into next-generation photovoltaic devices and modules.
Figure credit: Jonas Valentijn
Key publications include:
Van de Voorde, Mathis, Andersons, Janis & Saive, Rebecca. High aspect ratio triangular front contacts for solar cells fabricated by string‐printing. Progress in Photovoltaics: Research and Applications, 31(9), 960-968 (2023).
In-operando microscopy of charge transport and interfaces
A third major research line focuses on understanding charge transport in operating optoelectronic devices. Interfaces often dominate device performance, yet their transport properties are difficult to predict from materials parameters alone.
We develop and apply advanced in-operando Kelvin probe force microscopy (KPFM) and related scanning probe methods to visualize electrostatic potential and transport bottlenecks directly during operation. This work builds on earlier pioneering studies of potential distributions in organic solar cells and is now being extended toward new in-operando and time-resolved methods for photovoltaics, 2D materials, and semiconductor devices.
In collaboration with instrumentation partners, including Park Systems, we are developing new SPM methodologies that make these techniques more powerful and accessible for real device studies. Our long-term goal is to provide experimentally grounded insight into interfaces that enables more predictive and data-driven device development.
Video link:
Video credit: Zeinab Eftekhari
Key publications include:
Eftekhari, Zeinab, Ufer, Ariane, Wurstbauer, Ursula & Saive, Rebecca. Synchronized modulation Kelvin probe force microscopy for surface photovoltage studies in optoelectronic systems. MRS Communications, 1-7 (2026).
Beyond solar cells
While solar energy is the main focus of the group, many of the underlying concepts we study are relevant more broadly to optoelectronics, nanophysics, photonics, and semiconductors. Our research therefore also connects to hybrid devices, semiconductor interfaces, nanoscale energy conversion, and other emerging platforms in which light–matter interaction and charge transport are central.
Examples include:
Rezaei, Nasim, Eftekhari, Zeinab, Zheng, Jian-Yao & Saive, Rebecca. Performance analysis of on-chip coupled piezo/photodiodes, a numerical study. Sensors and Actuators A: Physical, 363, 114690 (2023).
Methods
Our research combines theory-guided experimental physics with device-oriented prototyping. Depending on the project, we use:
- computational optical and device simulations,
- spectro-angular characterization,
- advanced micro- and nanofabrication,
- Kelvin probe force microscopy and related scanning probe methods,
- and practical device testing under realistic conditions.
We work across length scales, from nanoscale interfaces to module-relevant optical systems, and place strong emphasis on connecting physical understanding to technological opportunity.
Specialized equipment
PLQY setup:
Our custom photoluminescence quantum yield (PLQY) measurement setup allows for absolute PLQY measurements with calibration between 200 nm and 1100 nm.
Park Systems SPM with synchronized illumination:
Our Park Systems SPM with synchronized illumination allows for photovoltage and bias induced voltage microscopy of functioning electronic devices under operation conditions (in-operando) with nanometer lateral resolution, pm vertical resolution and 100 micro second temporal resolution. In it's free time, it can also take high-resolution standard AFM and KPFM images.
Research philosophy
The group operates at the interface of fundamental science and implementation. We aim to discover physical mechanisms that matter, understand them in depth, and translate them into concepts that can shape future solar-energy technologies. This includes not only academic output, but also patents, industrial collaboration, entrepreneurship, and broader engagement with the innovation ecosystem.
See for example:
https://www.science-to-impact.nl/nl/verhalen/een-startup-vergroot-toch-juist-je-aanzien