TY - JOUR A1 - Yu, Jinde A1 - Xing, Yifan A1 - Shen, Zichao A1 - Zhu, Yuanwei A1 - Neher, Dieter A1 - Koch, Norbert A1 - Lu, Guanghao T1 - Infrared spectroscopy depth profiling of organic thin films JF - Materials horizons N2 - Organic thin films are widely used in organic electronics and coatings. Such films often feature film-depth dependent variations of composition and optoelectronic properties. State-of-the-art depth profiling methods such as mass spectroscopy and photoelectron spectroscopy rely on non-intrinsic species (vaporized ions, etching-induced surface defects), which are chemically and functionally different from the original materials. Here we introduce an easily-accessible and generally applicable depth profiling method: film-depth-dependent infrared (FDD-IR) spectroscopy profilometry based on directly measuring the intrinsic material after incremental surface-selective etching by a soft plasma, to study the material variations along the surface-normal direction. This depth profiling uses characteristic vibrational signatures of the involved compounds, and can be used for both conjugated and non-conjugated, neutral and ionic materials. A film-depth resolution of one nanometer is achieved. We demonstrate the application of this method for investigation of device-relevant thin films, including organic field-effect transistors and organic photovoltaic cells, as well as ionized dopant distributions in doped semiconductors. Y1 - 2021 U6 - https://doi.org/10.1039/d0mh02047h SN - 2051-6347 SN - 2051-6355 VL - 8 IS - 5 SP - 1461 EP - 1471 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Odziomek, Mateusz A1 - Giusto, Paolo A1 - Kossmann, Janina A1 - Tarakina, Nadezda A1 - Heske, Julian A1 - Rivadeneira, Salvador M. A1 - Keil, Waldemar A1 - Schmidt, Claudia A1 - Mazzanti, Stefano A1 - Savateev, Oleksandr A1 - Perdigon-Toro, Lorena A1 - Neher, Dieter A1 - Kühne, Thomas D. A1 - Antonietti, Markus A1 - Lopez-Salas, Nieves T1 - "Red Carbon": a rediscovered covalent crystalline semiconductor JF - Advanced materials N2 - Carbon suboxide (C3O2) is a unique molecule able to polymerize spontaneously into highly conjugated light-absorbing structures at temperatures as low as 0 degrees C. Despite obvious advantages, little is known about the nature and the functional properties of this carbonaceous material. In this work, the aim is to bring "red carbon," a forgotten polymeric semiconductor, back to the community's attention. A solution polymerization process is adapted to simplify the synthesis and control the structure. This allows one to obtain this crystalline covalent material at low temperatures. Both spectroscopic and elemental analyses support the chemical structure represented as conjugated ladder polypyrone ribbons. Density functional theory calculations suggest a crystalline structure of AB stacks of polypyrone ribbons and identify the material as a direct bandgap semiconductor with a medium bandgap that is further confirmed by optical analysis. The material shows promising photocatalytic performance using blue light. Moreover, the simple condensation-aromatization route described here allows the straightforward fabrication of conjugated ladder polymers and can be inspiring for the synthesis of carbonaceous materials at low temperatures in general. KW - carbon suboxide KW - carbonaceous materials KW - conjugated ladder polymers KW - covalent materials KW - photocatalysts Y1 - 2022 U6 - https://doi.org/10.1002/adma.202206405 SN - 0935-9648 SN - 1521-4095 VL - 34 IS - 40 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Warby, Jonathan A1 - Zu, Fengshuo A1 - Zeiske, Stefan A1 - Gutierrez-Partida, Emilio A1 - Frohloff, Lennart A1 - Kahmann, Simon A1 - Frohna, Kyle A1 - Mosconi, Edoardo A1 - Radicchi, Eros A1 - Lang, Felix A1 - Shah, Sahil A1 - Pena-Camargo, Francisco A1 - Hempel, Hannes A1 - Unold, Thomas A1 - Koch, Norbert A1 - Armin, Ardalan A1 - De Angelis, Filippo A1 - Stranks, Samuel D. A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - Understanding performance limiting interfacial recombination in pin Perovskite solar cells JF - Advanced energy materials N2 - Perovskite semiconductors are an attractive option to overcome the limitations of established silicon based photovoltaic (PV) technologies due to their exceptional opto-electronic properties and their successful integration into multijunction cells. However, the performance of single- and multijunction cells is largely limited by significant nonradiative recombination at the perovskite/organic electron transport layer junctions. In this work, the cause of interfacial recombination at the perovskite/C-60 interface is revealed via a combination of photoluminescence, photoelectron spectroscopy, and first-principle numerical simulations. It is found that the most significant contribution to the total C-60-induced recombination loss occurs within the first monolayer of C-60, rather than in the bulk of C-60 or at the perovskite surface. The experiments show that the C-60 molecules act as deep trap states when in direct contact with the perovskite. It is further demonstrated that by reducing the surface coverage of C-60, the radiative efficiency of the bare perovskite layer can be retained. The findings of this work pave the way toward overcoming one of the most critical remaining performance losses in perovskite solar cells. KW - C60 KW - defects KW - interface recombination KW - loss mechanisms KW - perovskites KW - solar cells Y1 - 2022 U6 - https://doi.org/10.1002/aenm.202103567 SN - 1614-6832 SN - 1614-6840 VL - 12 IS - 12 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Brinkmann, Kai Oliver A1 - Becker, Tim A1 - Zimmermann, Florian A1 - Kreusel, Cedric A1 - Gahlmann, Tobias A1 - Theisen, Manuel A1 - Haeger, Tobias A1 - Olthof, Selina A1 - Tückmantel, Christian A1 - Günster, M. A1 - Maschwitz, Timo A1 - Göbelsmann, Fabian A1 - Koch, Christine A1 - Hertel, Dirk A1 - Caprioglio, Pietro A1 - Peña-Camargo, Francisco A1 - Perdigón-Toro, Lorena A1 - Al-Ashouri, Amran A1 - Merten, Lena A1 - Hinderhofer, Alexander A1 - Gomell, Leonie A1 - Zhang, Siyuan A1 - Schreiber, Frank A1 - Albrecht, Steve A1 - Meerholz, Klaus A1 - Neher, Dieter A1 - Stolterfoht, Martin A1 - Riedl, Thomas T1 - Perovskite-organic tandem solar cells with indium oxide interconnect JF - Nature N2 - Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures(1). Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported(2-5). Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells(6,7). Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite-organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (V-oc) of wide-gap perovskite cells(8) and losses introduced by the interconnect between the subcells(9,10). Here we demonstrate perovskite-organic tandem cells with an efficiency of 24.0 per cent (certified 23.1 per cent) and a high V-oc of 2.15 volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high V-oc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells(11), show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately 1.5 nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite-organic tandems, which outperform the best p-i-n perovskite single junctions(12) and are on a par with perovskite-CIGS and all-perovskite multijunctions(13). Y1 - 2022 U6 - https://doi.org/10.1038/s41586-022-04455-0 SN - 0028-0836 SN - 1476-4687 VL - 604 IS - 7905 SP - 280 EP - 286 PB - Nature Research CY - Berlin ER - TY - JOUR A1 - Pranav, Manasi A1 - Hultzsch, Thomas A1 - Musiienko, Artem A1 - Sun, Bowen A1 - Shukla, Atul A1 - Jaiser, Frank A1 - Shoaee, Safa A1 - Neher, Dieter T1 - Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells JF - APL materials : high impact open access journal in functional materials science N2 - Understanding the origin of inefficient photocurrent generation in organic solar cells with low energy offset remains key to realizing high-performance donor-acceptor systems. Here, we probe the origin of field-dependent free-charge generation and photoluminescence in wnon-fullereneacceptor (NFA)-based organic solar cells using the polymer PM6 and the NFA Y5-a non-halogenated sibling to Y6, with a smaller energetic offset to PM6. By performing time-delayed collection field (TDCF) measurements on a variety of samples with different electron transport layers and active layer thickness, we show that the fill factor and photocurrent are limited by field-dependent free charge generation in the bulk of the blend. We also introduce a new method of TDCF called m-TDCF to prove the absence of artifacts from non-geminate recombination of photogenerated and dark charge carriers near the electrodes. We then correlate free charge generation with steady-state photoluminescence intensity and find perfect anticorrelation between these two properties. Through this, we conclude that photocurrent generation in this low-offset system is entirely controlled by the field-dependent dissociation of local excitons into charge-transfer states. (c) 2023 Author(s). Y1 - 2023 U6 - https://doi.org/10.1063/5.0151580 SN - 2166-532X VL - 11 IS - 6 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Perdigón-Toro, Lorena A1 - Le Quang Phuong, A1 - Eller, Fabian A1 - Freychet, Guillaume A1 - Saglamkaya, Elifnaz A1 - Khan, Jafar A1 - Wei, Qingya A1 - Zeiske, Stefan A1 - Kroh, Daniel A1 - Wedler, Stefan A1 - Koehler, Anna A1 - Armin, Ardalan A1 - Laquai, Frederic A1 - Herzig, Eva M. A1 - Zou, Yingping A1 - Shoaee, Safa A1 - Neher, Dieter T1 - Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages JF - Advanced energy materials N2 - Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder. Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied. By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity. Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation. It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend. KW - energetic disorder KW - non-fullerene acceptors KW - open-circuit voltage KW - organic solar cells Y1 - 2022 U6 - https://doi.org/10.1002/aenm.202103422 SN - 1614-6832 SN - 1614-6840 VL - 12 IS - 12 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Lang, Felix A1 - Köhnen, Eike A1 - Warby, Jonathan A1 - Xu, Ke A1 - Grischek, Max A1 - Wagner, Philipp A1 - Neher, Dieter A1 - Korte, Lars A1 - Albrecht, Steve A1 - Stolterfoht, Martin T1 - Revealing fundamental efficiency limits of monolithic perovskite/silicon tandem photovoltaics through subcell characterization JF - ACS Energy Letters N2 - Perovskite/silicon tandem photovoltaics (PVs) promise to accelerate the decarbonization of our energy systems. Here, we present a thorough subcell diagnosis methodology to reveal deep insights into the practical efficiency limitations of state-of-the-art perovskite/silicon tandem PVs. Our subcell selective intensity-dependent photoluminescence (PL) and injection-dependent electroluminescence (EL) measurements allow independent assessment of pseudo-V-OC and power conversion efficiencies (PCEs) for both subcells. We reveal identical metrics from PL and EL, which implies well-aligned energy levels throughout the entire cell. Relatively large ideality factors and insufficient charge extraction, however, cause each a fill factor penalty of about 6% (absolute). Using partial device stacks, we then identify significant losses in standard perovskite subcells due to bulk and interfacial recombination. Lastly, we present strategies to minimize these losses using triple halide (CsFAPb(IBrCI)(3)) based perovskites. Our results give helpful feedback for device development and lay the foundation toward advanced perovskite/silicon tandem PVs capable of exceeding 33% PCE. Y1 - 2021 U6 - https://doi.org/10.1021/acsenergylett.1c01783 SN - 2380-8195 VL - 6 IS - 11 SP - 3982 EP - 3991 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Neusser, David A1 - Sun, Bowen A1 - Tan, Wen Liang A1 - Thomsen, Lars A1 - Schultz, Thorsten A1 - Perdigon-Toro, Lorena A1 - Koch, Norbert A1 - Shoaee, Safa A1 - McNeill, Christopher R. A1 - Neher, Dieter A1 - Ludwigs, Sabine T1 - Spectroelectrochemically determined energy levels of PM6:Y6 blends and their relevance to solar cell performance JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Recent advances in organic solar cell performance have been mainly driven forward by combining high-performance p-type donor-acceptor copolymers (e.g.PM6) and non-fullerene small molecule acceptors (e.g.Y6) as bulk-heterojunction layers. A general observation in such devices is that the device performance, e.g., the open-circuit voltage, is strongly dependent on the processing solvent. While the morphology is a typically named key parameter, the energetics of donor-acceptor blends are equally important, but less straightforward to access in the active multicomponent layer. Here, we propose to use spectral onsets during electrochemical cycling in a systematic spectroelectrochemical study of blend films to access the redox behavior and the frontier orbital energy levels of the individual compounds. Our study reveals that the highest occupied molecular orbital offset (Delta E-HOMO) in PM6:Y6 blends is similar to 0.3 eV, which is comparable to the binding energy of Y6 excitons and therefore implies a nearly zero driving force for the dissociation of Y6 excitons. Switching the PM6 orientation in the blend films from face-on to edge-on in bulk has only a minor influence on the positions of the energy levels, but shows significant differences in the open circuit voltage of the device. We explain this phenomenon by the different interfacial molecular orientations, which are known to affect the non-radiative decay rate of the charge-transfer state. We compare our results to ultraviolet photoelectron spectroscopy data, which shows distinct differences in the HOMO offsets in the PM6:Y6 blend compared to neat films. This highlights the necessity to measure the energy levels of the individual compounds in device-relevant blend films. Y1 - 2022 U6 - https://doi.org/10.1039/d2tc01918c SN - 2050-7526 SN - 2050-7534 VL - 10 IS - 32 SP - 11565 EP - 11578 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Yuan, Jun A1 - Zhang, Chujun A1 - Qiu, Beibei A1 - Liu, Wei A1 - So, Shu Kong A1 - Mainville, Mathieu A1 - Leclerc, Mario A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Zou, Yingping T1 - Effects of energetic disorder in bulk heterojunction organic solar cells JF - Energy & environmental science N2 - Organic solar cells (OSCs) have progressed rapidly in recent years through the development of novel organic photoactive materials, especially non-fullerene acceptors (NFAs). Consequently, OSCs based on state-of-the-art NFAs have reached significant milestones, such as similar to 19% power conversion efficiencies (PCEs) and small energy losses (less than 0.5 eV). Despite these significant advances, understanding of the interplay between molecular structure and optoelectronic properties lags significantly behind. For example, despite the theoretical framework for describing the energetic disorder being well developed for the case of inorganic semiconductors, the question of the applicability of classical semiconductor theories in analyzing organic semiconductors is still under debate. A general observation in the inorganic field is that inorganic photovoltaic materials possessing a polycrystalline microstructure exhibit suppressed disorder properties and better charge carrier transport compared to their amorphous analogs. Accordingly, this principle extends to the organic semiconductor field as many organic photovoltaic materials are synthesized to pursue polycrystalline-like features. Yet, there appears to be sporadic examples that exhibit an opposite trend. However, full studies decoupling energetic disorder from aggregation effects have largely been left out. Hence, the potential role of the energetic disorder in OSCs has received little attention. Interestingly, recently reported state-of-the-art NFA-based devices could achieve a small energetic disorder and high PCE at the same time; and interest in this investigation related to the disorder properties in OSCs was revived. In this contribution, progress in terms of the correlation between molecular design and energetic disorder is reviewed together with their effects on the optoelectronic mechanism and photovoltaic performance. Finally, the specific challenges and possible solutions in reducing the energetic disorder of OSCs from the viewpoint of materials and devices are proposed. Y1 - 2022 U6 - https://doi.org/10.1039/d2ee00271j SN - 1754-5692 SN - 1754-5706 VL - 15 IS - 7 SP - 2806 EP - 2818 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kroh, Daniel A1 - Eller, Fabian A1 - Schötz, Konstantin A1 - Wedler, Stefan A1 - Perdigón-Toro, Lorena A1 - Freychet, Guillaume A1 - Wei, Qingya A1 - Dörr, Maximilian A1 - Jones, David A1 - Zou, Yingping A1 - Herzig, Eva M. A1 - Neher, Dieter A1 - Köhler, Anna T1 - Identifying the signatures of intermolecular interactions in blends of PM6 with Y6 and N4 using absorption spectroscopy JF - Advanced functional materials N2 - In organic solar cells, the resulting device efficiency depends strongly on the local morphology and intermolecular interactions of the blend film. Optical spectroscopy was used to identify the spectral signatures of interacting chromophores in blend films of the donor polymer PM6 with two state-of-the-art nonfullerene acceptors, Y6 and N4, which differ merely in the branching point of the side chain. From temperature-dependent absorption and luminescence spectroscopy in solution, it is inferred that both acceptor materials form two types of aggregates that differ in their interaction energy. Y6 forms an aggregate with a predominant J-type character in solution, while for N4 molecules the interaction is predominantly in a H-like manner in solution and freshly spin-cast film, yet the molecules reorient with respect to each other with time or thermal annealing to adopt a more J-type interaction. The different aggregation behavior of the acceptor materials is also reflected in the blend films and accounts for the different solar cell efficiencies reported with the two blends. KW - charge-transfer states KW - Frank-Condon analysis KW - morphology KW - organic solar cells Y1 - 2022 U6 - https://doi.org/10.1002/adfm.202205711 SN - 1616-301X SN - 1616-3028 VL - 32 IS - 44 PB - Wiley-VCH CY - Weinheim ER -