Featured Publications Q2-2026

Progress in Photovoltaics: Research and Applications | 2026; 34:367–395

Gernot Oreski, Chiara Barretta, Petra Christöfl, Paul Gebhardt, Karl-Anders Weiß, David C. Miller, Soňa Uličná, Michael Kempe, Laura S. Bruckman, Alessandro Virtuani, Hengyu Li, Brian Habersberger, Jeff Munro, Kristof Proost, Marcel Kühne

In recent years, photovoltaic (PV) encapsulant films marketed as polyolefins (POs), more specifically as PO elastomers (POEs) and thermoplastic POs (TPOs), have gained significant market share and are projected to become the dominant encapsulation films by 2030. Relative to other industries, there are significant misconceptions about the term PO in the PV industry. Both in the scientific literature as well as in sales and advertising, the terms PO, POE, and TPO are often misused to describe the same type of material with comparable properties, while in reality these may each consist of separate material classes.

A group of internationally leading experts therefore addressed the issue to improve clarity in the industry and avoid misunderstandings. This paper provides a comprehensive literature and market review, to showcase a broad range of PO and other ethylene copolymer encapsulants from recent studies and discusses the materials' properties to clarify what constitutes a “polyolefin.”

In addition, to promote a clearer comparison of encapsulant properties, we propose a two-dimensional taxonomy to categorize polymers used in module manufacturing. In terms of improving the reliability of solar PV modules, PO-based encapsulants have several advantages, but might come with disadvantages too. All this might prospectively impact adhesion properties of the encapsulant to other materials' interfaces (glass, cells etc.) and end-product quality. Because the track record of field-deployed PV modules containing PO encapsulants is limited, we hope to contribute to better material understanding and precision in communication in PV to secure quality.

Electrical Power and Energy Systems 177 (2026) 111827

Jakob Ungerland, Wolfgang Biener, Christian Schöll

The power system transformation towards high shares of converter-based renewable generation requires reliable stability assessments. To perform these calculations with a reasonable computational effort, distribution networks are often represented by highly simplified equivalent models. However, common methods such as the REI approach can distort the representation of the dynamic behavior and mask critical instabilities.

This work introduces the General Clustering Approach (GCA), a new method that represents active distribution networks more realistically by means of equivalent models. GCA aggregates generators and loads while taking network topology and voltage sensitivities into account and includes both grid-following and grid-forming converters. In multiple scenarios with different grid strengths and shares of grid-forming converters, GCA is systematically compared with established methods (including REI).

The results show that the distribution network representations currently used in practice do not allow for meaningful stability analyses of future converter-dominated systems. In particular, the widely used REI method frequently fails to detect instabilities. By contrast, the newly proposed GCA stays within all validation thresholds in all scenarios, while reducing model size by 86 % and simulation time by 79 % compared with the detailed model. For future converter-dominated power systems, equivalent networks should therefore be constructed using clustering methods such as GCA to ensure reliable stability assessments.

Communications Engineering | ( 2026) 5:78

Juan F. Martínez, Jens Ohlmann, Tom Smolinka & Frank Dimroth

Hydrogen produced with renewable energy helps smooth out the fluctuating nature of solar and wind power. The energy stored in hydrogen can later be turned back into electricity using fuel cells, or used in industrial processes, as well as in heating and gas networks. Several current production methods are still relatively inefficient. In the article, we present a highly efficient solar electrolysis module that splits water using electricity from advanced multi junction solar cells. A compact Fresnel lens array concentrates the direct sunlight onto the cells, which generate more than 4 volts – enough to power two polymer electrolyte membrane (PEM) electrolyzer cells connected in series. In outdoor tests, a demonstrator with a lens area of 64 cm² converted up to 31.3% of incoming sunlight into chemical energy stored in hydrogen (measured using hydrogen’s higher heating value).

EES Sol., 2026, Advance Article

Jared Faisst, Mathias List, Leonie Pap, Reid Patterson, Uli Würfel and Andreas W. Bett

Organic photovoltaics (OPVs) are an emerging photovoltaic technology characterized by their versatile application potential, such as flexible and semi-transparent devices. The photoactive layer in OPVs consists of a mixture of organic donor and acceptor

materials that form an interpenetrating network. This architecture is required because light absorption initially generates excitons, which are still bound to individual molecules and must reach an interface for it to dissociate, thereby generating free charge carriers and contribute to the photocurrent. The efficiency of this exciton dissociation process depends on multiple factors, such as the coarseness of the such as the structural scale of the interpenetrating network of materials, the exciton diffusion length, and the energetic landscape at the interface. Reliable quantification of the exciton dissociation efficiency is therefore essential for gaining insight into the performance of the organic photoactive layer and for guiding further optimization. 

Conventionally, this quantity is approximated by the internal quantum efficiency (IQE), that is, the measured short circuit current density divided by the expected current density from optical simulations. However, this approach leads to statistic uncertainties in the range of 5%. Furthermore, necessary assumptions for this approximation further introduce systematic uncertainty. In this work, we present a novel experimental approach that enables quantification of this efficiency with an uncertainty that is an order of magnitude lower than that of conventional IQE–based estimates. This was achieved by implementing two key steps:

First, the photoluminescence of excitons is used as a metric that is proportional to non-dissociation. Second, a comparative analysis is established by including an additional organic solar cell with a different morphology. The latter is achieved by increasing the acceptor content, thereby enlarging the acceptor volumes leading to an intentionally reduced exciton dissociation. Analyzing only the relative change of current density and exciton photoluminescence with respect to the generation in the respective photoactive layers is then sufficient to determine the exciton dissociation efficiency in both devices. As a result exciton dissociation efficiencies of 96.2 ± 0.4% for the system D18:Y6 and 97.2 ± 0.6% for PM6:DTY6 could be determined, showing that the method yields significantly more precise results.