TY - GEN A1 - Ye, Fangyuan A1 - Zhang, Shuo A1 - Warby, Jonathan A1 - Wu, Jiawei A1 - Gutierrez-Partida, Emilio A1 - Lang, Felix A1 - Shah, Sahil A1 - Saglamkaya, Elifnaz A1 - Sun, Bowen A1 - Zu, Fengshuo A1 - Shoaee, Safa A1 - Wang, Haifeng A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Zhu, Wei-Hong A1 - Stolterfoht, Martin A1 - Wu, Yongzhen T1 - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1317 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-587705 SN - 1866-8372 IS - 1317 ER - TY - JOUR A1 - Pena-Camargo, Francisco A1 - Thiesbrummel, Jarla A1 - Hempel, Hannes A1 - Musiienko, Artem A1 - Le Corre, Vincent M. A1 - Diekmann, Jonas A1 - Warby, Jonathan A1 - Unold, Thomas A1 - Lang, Felix A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - Revealing the doping density in perovskite solar cells and its impact on device performance JF - Applied physics reviews N2 - Traditional inorganic semiconductors can be electronically doped with high precision. Conversely, there is still conjecture regarding the assessment of the electronic doping density in metal-halide perovskites, not to mention of a control thereof. This paper presents a multifaceted approach to determine the electronic doping density for a range of different lead-halide perovskite systems. Optical and electrical characterization techniques, comprising intensity-dependent and transient photoluminescence, AC Hall effect, transfer-length-methods, and charge extraction measurements were instrumental in quantifying an upper limit for the doping density. The obtained values are subsequently compared to the electrode charge per cell volume under short-circuit conditions ( CUbi/eV), which amounts to roughly 10(16) cm(-3). This figure of merit represents the critical limit below which doping-induced charges do not influence the device performance. The experimental results consistently demonstrate that the doping density is below this critical threshold 10(12) cm(-3), which means << CUbi / e V) for all common lead-based metal-halide perovskites. Nevertheless, although the density of doping-induced charges is too low to redistribute the built-in voltage in the perovskite active layer, mobile ions are present in sufficient quantities to create space-charge-regions in the active layer, reminiscent of doped pn-junctions. These results are well supported by drift-diffusion simulations, which confirm that the device performance is not affected by such low doping densities. Y1 - 2022 U6 - https://doi.org/10.1063/5.0085286 SN - 1931-9401 VL - 9 IS - 2 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Mattern, Maximilian A1 - Reppert, Alexander von A1 - Zeuschner, Steffen Peer A1 - Pudell, Jan-Etienne A1 - Kühne, F. A1 - Diesing, Detlef A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics JF - Applied physics letters N2 - We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds. Y1 - 2022 U6 - https://doi.org/10.1063/5.0080378 SN - 0003-6951 SN - 1077-3118 VL - 120 IS - 9 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Reppert, Alexander von A1 - Puddell, J. A1 - Koc, A. A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet JF - Structural dynamics N2 - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. Y1 - 2016 U6 - https://doi.org/10.1063/1.4961253 SN - 2329-7778 VL - 3 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Le Corre, Vincent M. A1 - Diekmann, Jonas A1 - Peña-Camargo, Francisco A1 - Thiesbrummel, Jarla A1 - Tokmoldin, Nurlan A1 - Gutierrez-Partida, Emilio A1 - Peters, Karol Pawel A1 - Perdigón-Toro, Lorena A1 - Futscher, Moritz H. A1 - Lang, Felix A1 - Warby, Jonathan A1 - Snaith, Henry J. A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - Quantification of efficiency losses due to mobile ions in Perovskite solar cells via fast hysteresis measurements JF - Solar RRL N2 - Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady-state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via "fast-hysteresis" measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds (approximate to 1000 V s(-1)). The "ion-free" PCE is between 1% and 3% higher than the steady-state PCE, demonstrating the importance of ion-induced losses, even in cells with low levels of hysteresis at typical scan speeds (approximate to 100mv s(-1)). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast-hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments. KW - hysteresis KW - mobile ions KW - perovskite solar cells Y1 - 2021 U6 - https://doi.org/10.1002/solr.202100772 SN - 2367-198X VL - 6 IS - 4 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zeiske, Stefan A1 - Sandberg, Oskar J. A1 - Zarrabi, Nasim A1 - Wolff, Christian Michael A1 - Raoufi, Meysam A1 - Peña-Camargo, Francisco A1 - Gutierrez-Partida, Emilio A1 - Meredith, Paul A1 - Stolterfoht, Martin A1 - Armin, Ardalan T1 - Static disorder in lead halide perovskites JF - The journal of physical chemistry letters N2 - In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.0 +/- 1.0, 13.2 +/- 1.0, and 13.5 +/- 1.0 meV for single, double, and triple cation perovskite. Static, temperature-independent contributions to the Urbach energy are found to be as low as 5.1 ?+/- 0.5, 4.7 +/- 0.3, and 3.3 +/- 0.9 meV for the same systems. Our results suggest that, at a low temperature, the dominant static disorder in perovskites is derived from zero-point phonon energy rather than structural disorder. This is unusual for solution-processed semiconductors but broadens the potential application of perovskites further to quantum electronics and devices. KW - Cations KW - External quantum efficiency KW - Perovskites KW - Solar cells KW - Solar energy Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpclett.2c01652 SN - 1948-7185 VL - 13 IS - 31 SP - 7280 EP - 7285 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - Maznev, A. A. A1 - Herzog, Marc A1 - Kronseder, M. A1 - Back, Christian H. A1 - Malinowski, Gregory A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction JF - Nature Communications N2 - Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron-phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-05693-5 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - Reppert, Alexander von A1 - Schick, D. A1 - Zamponi, F. A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Zabel, Hartmut A1 - Bargheer, Matias T1 - Ultrafast negative thermal expansion driven by spin disorder JF - Physical review : B, Condensed matter and materials physics N2 - We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium, and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion, which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho [Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign traveling through the heterostructure. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.99.094304 SN - 2469-9950 SN - 2469-9969 VL - 99 IS - 9 PB - American Physical Society CY - College Park ER - TY - THES A1 - Perdigón-Toro, Lorena T1 - On the Generation and Fate of Free Carriers in Non-Fullerene Acceptor Organic Solar Cells N2 - Organic solar cells offer an efficient and cost-effective alternative for solar energy harvesting. This type of photovoltaic cell typically consists of a blend of two organic semiconductors, an electron donating polymer and a low molecular weight electron acceptor to create what is known as a bulk heterojunction (BHJ) morphology. Traditionally, fullerene-based acceptors have been used for this purpose. In recent years, the development of new acceptor molecules, so-called non-fullerene acceptors (NFA), has breathed new life into organic solar cell research, enabling record efficiencies close to 19%. Today, NFA-based solar cells are approaching their inorganic competitors in terms of photocurrent generation, but lag in terms of open circuit voltage (V_OC). Interestingly, the V_OC of these cells benefits from small offsets of orbital energies at the donor-NFA interface, although previous knowledge considered large energy offsets to be critical for efficient charge carrier generation. In addition, there are several other electronic and structural features that distinguish NFAs from fullerenes. My thesis focuses on understanding the interplay between the unique attributes of NFAs and the physical processes occurring in solar cells. By combining various experimental techniques with drift-diffusion simulations, the generation of free charge carriers as well as their recombination in state-of-the-art NFA-based solar cells is characterized. For this purpose, solar cells based on the donor polymer PM6 and the NFA Y6 have been investigated. The generation of free charge carriers in PM6:Y6 is efficient and independent of electric field and excitation energy. Temperature-dependent measurements show a very low activation energy for photocurrent generation (about 6 meV), indicating barrierless charge carrier separation. Theoretical modeling suggests that Y6 molecules have large quadrupole moments, leading to band bending at the donor-acceptor interface and thereby reducing the electrostatic Coulomb dissociation barrier. In this regard, this work identifies poor extraction of free charges in competition with nongeminate recombination as a dominant loss process in PM6:Y6 devices. Subsequently, the spectral characteristics of PM6:Y6 solar cells were investigated with respect to the dominant process of charge carrier recombination. It was found that the photon emission under open-circuit conditions can be almost entirely attributed to the occupation and recombination of Y6 singlet excitons. Nevertheless, the recombination pathway via the singlet state contributes only 1% to the total recombination, which is dominated by the charge transfer state (CT-state) at the donor-acceptor interface. Further V_OC gains can therefore only be expected if the density and/or recombination rate of these CT-states can be significantly reduced. Finally, the role of energetic disorder in NFA solar cells is investigated by comparing Y6 with a structurally related derivative, named N4. Layer morphology studies combined with temperature-dependent charge transport experiments show significantly lower structural and energetic disorder in the case of the PM6:Y6 blend. For both PM6:Y6 and PM6:N4, disorder determines the maximum achievable V_OC, with PM6:Y6 benefiting from improved morphological order. Overall, the obtained findings point to avenues for the realization of NFA-based solar cells with even smaller V_OC losses. Further reduction of nongeminate recombination and energetic disorder should result in organic solar cells with efficiencies above 20% in the future. N2 - Organische Solarzellen bieten eine effiziente und kostengünstige Alternative für die Nutzung von Sonnenenergie. Bei dieser Art von Photovoltaikzellen werden in der Regel zwei organische Halbleiter, ein elektronenspendendes Polymer und ein niedermolekularer Elektronenakzeptor gemischt, um eine sogenannte „Bulk-Heterojunction“ (BHJ)-Morphologie zu erzeugen. Traditionell wurden hierfür Fulleren-basierte Akzeptoren verwendet. In den letzten Jahren hat die Entwicklung neuer Akzeptor-Moleküle, so genannter Nicht-Fulleren-Akzeptoren (NFA), der organischen Solarzellenforschung neues Leben eingehaucht und damit Rekordwirkungsgrade >19 % ermöglicht. Heutzutage nähern sich NFA-basierte Solarzellen ihren anorganischen Konkurrenten bezüglich der Photostromerzeugung an, nicht jedoch im Hinblick auf die Leerlaufspannung (V_OC). Interessanterweise profitiert der V_OC dieser Zellen von kleinen Offsets der Orbitalenergien an der Donor-NFA-Grenzfläche, obwohl nach bisherigem Wissen große Energieoffsets als entscheidend für die effiziente Ladungsträgergenerierung an der Heterogrenzfläche galten. Darüber hinaus gibt es eine Reihe weiterer elektronischer und struktureller Merkmale, die NFAs von Fullerenen unterscheiden. Meine Dissertation konzentriert sich auf ein tiefgreifendes Verständnis des Zusammenspiels der einzigartigen Eigenschaften von NFAs und den physikalischen Prozessen in daraus hergestellten Solarzellen. Durch die Kombination verschiedener experimenteller Techniken mit Drift-Diffusions-Simulationen wird die Erzeugung freier Ladungsträger sowie deren Rekombination in modernen NFA-basierten Solarzellen charakterisiert. Zu diesem Zweck wurden Solarzellen auf Basis des Donor-Polymers PM6 und des NFA Y6 untersucht. Die Erzeugung freier Ladungsträger in PM6:Y6 erweist sich dabei als effizient und unabhängig von elektrischem Feld und Anregungsenergie. Temperaturabhängige Messungen zeigen eine sehr geringe Aktivierungsenergie für die Photostromerzeugung (ca. 6 meV), was auf eine barrierefreie Ladungsträgertrennung hinweist. Theoretische Modellierungen legen nahe, dass Y6-Moleküle große Quadrupolmomente aufweisen, was zu einer Bandverbiegung an der Donor-Akzeptor-Grenzfläche führt und dabei die elektrostatische Coulombsch-Dissoziationsbarriere reduziert. In dieser Hinsicht identifiziert diese Arbeit die schlechte Extraktion freier Ladungen in Konkurrenz zur „nongeminalen“ Rekombination als einen dominanten Verlustprozess in PM6:Y6 Zellen. In weiterer Folge wurden die spektralen Eigenschaften von PM6:Y6-Solarzellen im Hinblick auf den dominanten Prozess der Ladungsträgergenerierung und rekombination untersucht. Es zeigte sich, dass die Photonenemission unter Leerlaufbedingungen fast vollständig auf die Besetzung und Rekombination von Y6-Singlet-Exzitonen zurückgeführt werden kann. Trotzdem trägt der Rekombinationspfad über den Singlett-Zustand nur zu 1 % zur gesamten Rekombination bei, die über den Ladungstransfer-Zustand (CT-state) an der Donor-Akzeptor-Grenzfläche dominiert wird. Weitere V_OC Gewinne sind daher nur zu erwarten, wenn die Dichte und/oder die Rekombinationsrate dieser CT-Zustände erheblich reduziert werden kann. Schließlich wird die Rolle der energetischen Unordnung in NFA-Solarzellen durch den Vergleich von Y6 mit einem strukturverwandten Derivat, genannt N4, untersucht. Untersuchungen zur Schichtmorphologie in Kombination mit Experimenten zum temperaturabhängigen Ladungstransport zeigen eine deutlich geringere strukturelle und energetische Unordnung im Fall des PM6:Y6 Blends. Sowohl für PM6:Y6 als auch für PM6:N4 bestimmt die Unordnung den maximal erreichbaren V_OC, wobei PM6:Y6 von der verbesserten morphologischen Ordnung profitiert. Insgesamt weisen die gewonnenen Erkenntnisse Wege für die Realisierung von NFA-basierten Solarzellen mit noch kleineren V_OC-Verlusten auf. Durch die weitere Reduzierung der „nongeminaten“ Rekombination als auch der energetischen Unordnung sollten in Zukunft organische Solarzellen mit einem Wirkungsgrad von über 20 % möglich werden. T2 - Über die Photogenerierung und Rekombination freier Ladungsträger in organischen Solarzellen mit Nicht-Fulleren-Akzeptoren KW - organic solar cells KW - non-fullerene acceptors KW - free charge generation KW - free charge recombination KW - energetic disorder KW - organic semiconductors KW - energetische Unordnung KW - Generierung freier Ladungsträger KW - freie Ladungsträger Rekombination KW - Nicht-Fulleren-Akzeptoren KW - organische Halbleiter KW - organische Solarzellen Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-558072 ER - TY - JOUR A1 - Marin-Beloqui, Jose A1 - Zhang, Guanran A1 - Guo, Junjun A1 - Shaikh, Jordan A1 - Wohrer, Thibaut A1 - Hosseini, Seyed Mehrdad A1 - Sun, Bowen A1 - Shipp, James A1 - Auty, Alexander J. A1 - Chekulaev, Dimitri A1 - Ye, Jun A1 - Chin, Yi-Chun A1 - Sullivan, Michael B. A1 - Mozer, Attila J. A1 - Kim, Ji-Seon A1 - Shoaee, Safa A1 - Clarke, Tracey M. T1 - Insight into the origin of trapping in polymer/fullerene blends with a systematic alteration of the fullerene to higher adducts JF - Journal of physical chemistry C N2 - The bimolecular recombination characteristics of conjugated polymer poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,5-bis 3-tetradecylthiophen-2-y1 thiazolo 5,4-d thiazole)-2,5diy1] (PDTSiTTz) blended with the fullerene series PC60BM, ICMA, ICBA, and ICTA have been investigated using microsecond and femtosecond transient absorption spectroscopy, in conjunction with electroluminescence measurements and ambient photoemission spectroscopy. The non-Langevin polymer PDTSiTTz allows an inspection of intrinsic bimolecular recombination rates uninhibited by diffusion, while the low oscillator strengths of fullerenes allow polymer features to dominate, and we compare our results to those of the well-known polymer Si-PCPDTBT. Using mu s-TAS, we have shown that the trap -limited decay dynamics of the PDTSiTTz polaron becomes progressively slower across the fullerene series, while those of Si-PCPDTBT are invariant. Electroluminescence measurements showed an unusual double peak in pristine PDTSiTTz, attributed to a low energy intragap charge transfer state, likely interchain in nature. Furthermore, while the pristine PDTSiTTz showed a broad, low-intensity density of states, the ICBA and ICTA blends presented a virtually identical DOS to Si-PCPDTBT and its blends. This has been attributed to a shift from a delocalized, interchain highest occupied molecular orbital (HOMO) in the pristine material to a dithienosilole-centered HOMO in the blends, likely a result of the bulky fullerenes increasing interchain separation. This HOMO localization had a side effect of progressively shifting the polymer HOMO to shallower energies, which was correlated with the observed decrease in bimolecular recombination rate and increased "trap" depth. However, since the density of tail states remained the same, this suggests that the traditional viewpoint of "trapping" being dominated by tail states may not encompass the full picture and that the breadth of the DOS may also have a strong influence on bimolecular recombination. Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpcc.1c10378 SN - 1932-7447 SN - 1932-7455 VL - 126 IS - 5 SP - 2708 EP - 2719 PB - American Chemical Society CY - Washington ER -