Prof. Dr. Frédéric Laquai
Academic Research Focus
- Photophysics of excitonic solar cells
- Exciton dissociation, charge carrier generation, transport and recombination in polymer and small molecule organic and hybrid solar cells
- Steady-state and transient all-optical and electro-optical techniques e.g. transient absorption pump-probe spectroscopy and time-resolved photoluminescence spectroscopy
- Exciton dissociation, charge carrier generation, transport and recombination in polymer and small molecule organic and hybrid solar cells
- Steady-state and transient all-optical and electro-optical techniques e.g. transient absorption pump-probe spectroscopy and time-resolved photoluminescence spectroscopy
Fields of Application
Nanomaterials, Photo-(electro)catalysis, Solar Cells / Photovoltaics
Publications
4.
R Hooijer, S Kim, S Klenk, H Zhu, C Yilmaz, Y Yalcinkaya, D Im, A S Backeberg, J Huang, M Bouraoui, A Buyruk, E Ugur, C Maheu, A Hartschuh, F Laquai, L Schmidt‐Mende, G S Duesberg, S Lee, E Aydin
Synthetic Surface Design of Transparent Electrodes for Enhanced Molecular Contact in Perovskite Solar Cells Journal Article
In: Advanced Energy Materials, 2026, ISSN: 1614-6832.
@article{nokey,
title = {Synthetic Surface Design of Transparent Electrodes for Enhanced Molecular Contact in Perovskite Solar Cells},
author = {R Hooijer and S Kim and S Klenk and H Zhu and C Yilmaz and Y Yalcinkaya and D Im and A S Backeberg and J Huang and M Bouraoui and A Buyruk and E Ugur and C Maheu and A Hartschuh and F Laquai and L Schmidt‐Mende and G S Duesberg and S Lee and E Aydin},
url = {\<Go to ISI\>://WOS:001742244200001},
doi = {10.1002/aenm.70962},
issn = {1614-6832},
year = {2026},
date = {2026-04-16},
journal = {Advanced Energy Materials},
abstract = {Self-assembled molecules (SAMs) as a molecular charge selective contact and interface with metal oxides are the new benchmark in p-i-n devices. Yet, transparent electrode (i.e., ITO) surface preparation is often performed with established protocols that do not exploit the full potential of self-assembly. We introduce a simple, solution-based ITO surface treatment strategy that enables improved contact formation by simultaneously tuning surface chemistry, conductivity and homogeneity. Contrary to the prevailing assumption that maximizing surface hydroxylation is the key for phosphonic-acid-based SAMs, we show that synthetic design with moderate hydroxyl and hydroxide content yields more uniform and electronically favourable interfaces for SAM anchoring. Electronically, the resulting contacts enable enhanced charge extraction, while offering improved layer homogeneity and operational stability. The treated interfaces further demonstrate improved resilience under extreme thermal cycling between -80 degrees C and 80 degrees C, relevant for low-earth-orbit (LEO) space operation. Importantly, we demonstrated the broad applicability of our approach across various materials, fabrication environments, and device structures, including single junction and tandem solar cells. These findings establish surface preparation as a design parameter on par with molecular engineering for robust perovskite optoelectronic devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Self-assembled molecules (SAMs) as a molecular charge selective contact and interface with metal oxides are the new benchmark in p-i-n devices. Yet, transparent electrode (i.e., ITO) surface preparation is often performed with established protocols that do not exploit the full potential of self-assembly. We introduce a simple, solution-based ITO surface treatment strategy that enables improved contact formation by simultaneously tuning surface chemistry, conductivity and homogeneity. Contrary to the prevailing assumption that maximizing surface hydroxylation is the key for phosphonic-acid-based SAMs, we show that synthetic design with moderate hydroxyl and hydroxide content yields more uniform and electronically favourable interfaces for SAM anchoring. Electronically, the resulting contacts enable enhanced charge extraction, while offering improved layer homogeneity and operational stability. The treated interfaces further demonstrate improved resilience under extreme thermal cycling between -80 degrees C and 80 degrees C, relevant for low-earth-orbit (LEO) space operation. Importantly, we demonstrated the broad applicability of our approach across various materials, fabrication environments, and device structures, including single junction and tandem solar cells. These findings establish surface preparation as a design parameter on par with molecular engineering for robust perovskite optoelectronic devices.
3.
S Alam, J P Jurado, Z Xu, A D Sokeng, B Pal, M Ferree, X Y Jiang, S Simotko, G L Frey, U S Schubert, P Muller-Buschbaum, H Hoppe, F Laquai
Locally Resolved Thermally Induced Degradation of PM6:Y6-Based Organic Solar Cells Journal Article
In: Acs Applied Energy Materials, vol. 9, no. 3, pp. 1669-1679, 2026, ISSN: 2574-0962.
@article{nokey,
title = {Locally Resolved Thermally Induced Degradation of PM6:Y6-Based Organic Solar Cells},
author = {S Alam and J P Jurado and Z Xu and A D Sokeng and B Pal and M Ferree and X Y Jiang and S Simotko and G L Frey and U S Schubert and P Muller-Buschbaum and H Hoppe and F Laquai},
url = {\<Go to ISI\>://WOS:001674305400001},
doi = {10.1021/acsaem.5c03513},
issn = {2574-0962},
year = {2026},
date = {2026-02-09},
journal = {Acs Applied Energy Materials},
volume = {9},
number = {3},
pages = {1669-1679},
abstract = {The limited thermal stability of organic solar cells has hampered their commercialization. Therefore, it is crucial to gain in-depth insight into the underlying causes of thermal device instability and to develop practical approaches to reduce its impact. In this study, we examine thermal degradation processes of the donor/acceptor system PBDB-T-2F:BTP-4F (alias PM6:Y6) in bulk heterojunction polymer/nonfullerene acceptor (NFA) solar cells, considered as a state-of-the-art system of the organic photovoltaics (OPV) technology. More specifically, this study investigates the effects of varying postproduction annealing temperatures on the performance of solar cells and locally resolves the thermally induced impact on these solar cells using a set of advanced imaging techniques, including photoluminescence imaging (PLI), electroluminescence imaging (ELI), and light beam-induced current (LBIC) measurements.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The limited thermal stability of organic solar cells has hampered their commercialization. Therefore, it is crucial to gain in-depth insight into the underlying causes of thermal device instability and to develop practical approaches to reduce its impact. In this study, we examine thermal degradation processes of the donor/acceptor system PBDB-T-2F:BTP-4F (alias PM6:Y6) in bulk heterojunction polymer/nonfullerene acceptor (NFA) solar cells, considered as a state-of-the-art system of the organic photovoltaics (OPV) technology. More specifically, this study investigates the effects of varying postproduction annealing temperatures on the performance of solar cells and locally resolves the thermally induced impact on these solar cells using a set of advanced imaging techniques, including photoluminescence imaging (PLI), electroluminescence imaging (ELI), and light beam-induced current (LBIC) measurements.
2.
S Alam, C E Petoukhoff, J P Jurado, H Aldosari, X Jiang, T Váry, H A Nasser, A Dahman, W Althobaiti, S P G Lopez, W Alsufyani, P Müller-Buschbaum, V Nádaždy, H Hoppe, F Laquai
Influence of thermal annealing on microstructure, energetic landscape and device performance of P3HT:PCBM-based organic solar cells Journal Article
In: Journal of Physics: Energy, vol. 6, no. 2, pp. 025013, 2024, ISSN: 2515-7655.
@article{nokey,
title = {Influence of thermal annealing on microstructure, energetic landscape and device performance of P3HT:PCBM-based organic solar cells},
author = {S Alam and C E Petoukhoff and J P Jurado and H Aldosari and X Jiang and T V\'{a}ry and H A Nasser and A Dahman and W Althobaiti and S P G Lopez and W Alsufyani and P M\"{u}ller-Buschbaum and V N\'{a}da\v{z}dy and H Hoppe and F Laquai},
url = {https://dx.doi.org/10.1088/2515-7655/ad2498},
doi = {10.1088/2515-7655/ad2498},
issn = {2515-7655},
year = {2024},
date = {2024-03-14},
journal = {Journal of Physics: Energy},
volume = {6},
number = {2},
pages = {025013},
abstract = {Thermal annealing alters the morphology of organic donor-acceptor bulk-heterojunction thin films used in organic solar cells. Here, we studied the influence of thermal annealing on blends of amorphous regio-random (RRa) and semi-crystalline regio-regular (RR) poly (3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester. Since the P3HT:PCBM blend is one of the most studied in the OPV community, the existing research provides a solid foundation for us to compare and benchmark our innovative characterization techniques that have been previously under-utilized to investigate bulk heterojunction organic thin films. Here, we combine advanced novel microscopies and spectroscopies, including polarized light microscopy, photo-deflection spectroscopy, hyperspectral photoluminescence imaging, and energy resolved-electrochemical impedance spectroscopy, with structural characterization techniques, including grazing-incidence wide-angle x-ray scattering, grazing-incidence x-ray diffraction, and Raman spectroscopy, in order to reveal the impact of thermal annealing on the microstructural crystallinity and morphology of the photoactive layer in organic solar cells. Coupled transfer matrix and drift-diffusion simulations were used to study the impact of the density of states on the solar cells’ device performance parameters, namely the short-circuit current (J SC), open circuit voltage (V OC), fill factor (FF), and power conversion efficiency (PCE).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Thermal annealing alters the morphology of organic donor-acceptor bulk-heterojunction thin films used in organic solar cells. Here, we studied the influence of thermal annealing on blends of amorphous regio-random (RRa) and semi-crystalline regio-regular (RR) poly (3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester. Since the P3HT:PCBM blend is one of the most studied in the OPV community, the existing research provides a solid foundation for us to compare and benchmark our innovative characterization techniques that have been previously under-utilized to investigate bulk heterojunction organic thin films. Here, we combine advanced novel microscopies and spectroscopies, including polarized light microscopy, photo-deflection spectroscopy, hyperspectral photoluminescence imaging, and energy resolved-electrochemical impedance spectroscopy, with structural characterization techniques, including grazing-incidence wide-angle x-ray scattering, grazing-incidence x-ray diffraction, and Raman spectroscopy, in order to reveal the impact of thermal annealing on the microstructural crystallinity and morphology of the photoactive layer in organic solar cells. Coupled transfer matrix and drift-diffusion simulations were used to study the impact of the density of states on the solar cells’ device performance parameters, namely the short-circuit current (J SC), open circuit voltage (V OC), fill factor (FF), and power conversion efficiency (PCE).
1.
S Alam, H Aldosari, C E Petoukhoff, T Váry, W Althobaiti, M Alqurashi, H Tang, J I Khan, V Nádaždy, P Müller-Buschbaum, G C Welch, F Laquai
Thermally-Induced Degradation in PM6:Y6-Based Bulk Heterojunction Organic Solar Cells Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2308076, 2023, ISSN: 1616-301X.
@article{nokey,
title = {Thermally-Induced Degradation in PM6:Y6-Based Bulk Heterojunction Organic Solar Cells},
author = {S Alam and H Aldosari and C E Petoukhoff and T V\'{a}ry and W Althobaiti and M Alqurashi and H Tang and J I Khan and V N\'{a}da\v{z}dy and P M\"{u}ller-Buschbaum and G C Welch and F Laquai},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202308076},
doi = {https://doi.org/10.1002/adfm.202308076},
issn = {1616-301X},
year = {2023},
date = {2023-10-27},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2308076},
abstract = {Abstract Thermally induced degradation of organic photovoltaic devices hinders the commercialization of this emerging PV technology. Thus, a precise understanding of the origin of thermal device instability, as well as identifying strategies to circumvent degradation is of utmost importance. Here, it investigates thermally-induced degradation of state-of-the-art PBDB-T-2F (PM6):BTP (Y6) bulk heterojunction solar cells at different temperatures and reveal changes of their optical properties, photophysics, and morphology. The open-circuit voltage and fill factor of thermally degraded devices are limited by dissociation and charge collection efficiency differences, while the short-circuit current density is only slightly affected. Energy-resolved electrochemical impedance spectroscopy measurements reveal that thermally degraded samples exhibit a higher energy barrier for the charge-transfer state to charge-separated state conversion. Furthermore, the field dependence of charge generation, recombination, and extraction are studied by time-delayed collection field and transient photocurrent and photovoltage experiments, indicating significant bimolecular recombination limits device performance. Finally, coupled optical-electrical device simulations are conducted to fit the devices’ current-voltage characteristics, enabling us to find useful correlations between optical and electrical properties of the active layers and device performance parameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Thermally induced degradation of organic photovoltaic devices hinders the commercialization of this emerging PV technology. Thus, a precise understanding of the origin of thermal device instability, as well as identifying strategies to circumvent degradation is of utmost importance. Here, it investigates thermally-induced degradation of state-of-the-art PBDB-T-2F (PM6):BTP (Y6) bulk heterojunction solar cells at different temperatures and reveal changes of their optical properties, photophysics, and morphology. The open-circuit voltage and fill factor of thermally degraded devices are limited by dissociation and charge collection efficiency differences, while the short-circuit current density is only slightly affected. Energy-resolved electrochemical impedance spectroscopy measurements reveal that thermally degraded samples exhibit a higher energy barrier for the charge-transfer state to charge-separated state conversion. Furthermore, the field dependence of charge generation, recombination, and extraction are studied by time-delayed collection field and transient photocurrent and photovoltage experiments, indicating significant bimolecular recombination limits device performance. Finally, coupled optical-electrical device simulations are conducted to fit the devices’ current-voltage characteristics, enabling us to find useful correlations between optical and electrical properties of the active layers and device performance parameters.