@article{RaoufiHoermannLigorioetal.2020,
  author    = {Raoufi, Meysam and H{\"o}rmann, Ulrich and Ligorio, Giovanni and Hildebrandt, Jana and P{\"a}tzel, Michael and Schultz, Thorsten and Perdigon, Lorena and Koch, Norbert and List-Kratochvil, Emil and Hecht, Stefan and Neher, Dieter},
  title     = {Simultaneous effect of ultraviolet radiation and surface modification on the work function and hole injection properties of ZnO thin films},
  series = {Physica Status Solidi. A , Applications and materials science},
  volume    = {217},
  journal   = {Physica Status Solidi. A , Applications and materials science},
  number    = {5},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1862-6300},
  doi       = {10.1002/pssa.201900876},
  pages     = {1 -- 6},
  year      = {2020},
  abstract  = {The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions.},
  language  = {en}
}
@article{TaitReckwitzArvindetal.2021,
  author    = {Tait, Claudia E. and Reckwitz, Anna and Arvind, Malavika and Neher, Dieter and Bittl, Robert and Behrends, Jan},
  title     = {Spin-spin interactions and spin delocalisation in a doped organic semiconductor probed by EPR spectroscopy},
  series = {Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies},
  volume    = {23},
  journal   = {Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies},
  number    = {25},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1463-9076},
  doi       = {10.1039/d1cp02133h},
  pages     = {13827 -- 13841},
  year      = {2021},
  abstract  = {The enhancement and control of the electrical conductivity of organic semiconductors is fundamental for their use in optoelectronic applications and can be achieved by molecular doping, which introduces additional charge carriers through electron transfer between a dopant molecule and the organic semiconductor. Here, we use Electron Paramagnetic Resonance (EPR) spectroscopy to characterise the unpaired spins associated with the charges generated by molecular doping of the prototypical organic semiconductor poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) and tris(pentafluorophenyl)borane (BCF). The EPR results reveal the P3HT radical cation as the only paramagnetic species in BCF-doped P3HT films and show evidence for increased mobility of the detected spins at high doping concentrations as well as formation of antiferromagnetically coupled spin pairs leading to decreased spin concentrations at low temperatures. The EPR signature for F(4)TCNQ-doped P3HT is found to be determined by spin exchange between P3HT radical cations and F(4)TCNQ radical anions. Results from continuous-wave and pulse EPR measurements suggest the presence of the unpaired spin on P3HT in a multitude of environments, ranging from free P3HT radical cations with similar properties to those observed in BCF-doped P3HT, to pairs of dipolar and exchange-coupled spins on P3HT and the dopant anion. Characterisation of the proton hyperfine interactions by ENDOR allowed quantification of the extent of spin delocalisation and revealed reduced delocalisation in the F(4)TCNQ-doped P3HT films.},
  language  = {en}
}
@article{PerdigonToroLeQuangPhuongZeiskeetal.2021,
  author    = {Perdig{\´o}n-Toro, Lorena and Le Quang Phuong, and Zeiske, Stefan and Vandewal, Koen and Armin, Ardalan and Shoaee, Safa and Neher, Dieter},
  title     = {Excitons dominate the emission from PM6},
  series = {ACS energy letters / American Chemical Society},
  volume    = {6},
  journal   = {ACS energy letters / American Chemical Society},
  number    = {2},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2380-8195},
  doi       = {10.1021/acsenergylett.0c02572},
  pages     = {557 -- 564},
  year      = {2021},
  abstract  = {Non-fullerene acceptors (NFAs) are far more emissive than their fullerene-based counterparts. Here, we study the spectral properties of photocurrent generation and recombination of the blend of the donor polymer PM6 with the NFA Y6. We find that the radiative recombination of free charges is almost entirely due to the re-occupation and decay of Y6 singlet excitons, but that this pathway contributes less than 1\% to the total recombination. As such, the open-circuit voltage of the PM6:Y6 blend is determined by the energetics and kinetics of the charge-transfer (CT) state. Moreover, we find that no information on the energetics of the CT state manifold can be gained from the low-energy tail of the photovoltaic external quantum efficiency spectrum, which is dominated by the excitation spectrum of the Y6 exciton. We, finally, estimate the charge-separated state to lie only 120 meV below the Y6 singlet exciton energy, meaning that this blend indeed represents a high-efficiency system with a low energetic offset.},
  language  = {en}
}
@article{PranavBenduhnNymanetal.2021,
  author    = {Pranav, Manasi and Benduhn, Johannes and Nyman, Mathias and Hosseini, Seyed Mehrdad and Kublitski, Jonas and Shoaee, Safa and Neher, Dieter and Leo, Karl and Spoltore, Donato},
  title     = {Enhanced charge selectivity via anodic-C60 layer reduces nonradiative losses in organic solar cells},
  series = {ACS applied materials \& interfaces},
  volume    = {13},
  journal   = {ACS applied materials \& interfaces},
  number    = {10},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/acsami.1c00049},
  pages     = {12603 -- 12609},
  year      = {2021},
  abstract  = {Interfacial layers in conjunction with suitable charge-transport layers can significantly improve the performance of optoelectronic devices by facilitating efficient charge carrier injection and extraction. This work uses a neat C-60 interlayer on the anode to experimentally reveal that surface recombination is a significant contributor to nonradiative recombination losses in organic solar cells. These losses are shown to proportionally increase with the extent of contact between donor molecules in the photoactive layer and a molybdenum oxide (MoO3) hole extraction layer, proven by calculating voltage losses in low- and high-donor-content bulk heterojunction device architectures. Using a novel in-device determination of the built-in voltage, the suppression of surface recombination, due to the insertion of a thin anodic-C-60 interlayer on MoO3, is attributed to an enhanced built-in potential. The increased built-in voltage reduces the presence of minority charge carriers at the electrodes-a new perspective on the principle of selective charge extraction layers. The benefit to device efficiency is limited by a critical interlayer thickness, which depends on the donor material in bilayer devices. Given the high popularity of MoO3 as an efficient hole extraction and injection layer and the increasingly popular discussion on interfacial phenomena in organic optoelectronic devices, these findings are relevant to and address different branches of organic electronics, providing insights for future device design.},
  language  = {en}
}
@misc{ZimmermannKampeScholzetal.2024,
  author    = {Zimmermann, Matthias and Kampe, Heike and Scholz, Jana and Aust, Sarah-Madeleine and Horn-Conrad, Antje and Engel, Silke and Agrofylax, Luisa and Schlegel, Theresa and Mikulla, Stefanie and Albrecht, Anna Helena and Neher, Dieter and Himmler, Lena},
  title     = {Bildung:digital},
  series = {Portal Wissen: Das Forschungsmagazin der Universit{\"a}t Potsdam},
  journal   = {Portal Wissen: Das Forschungsmagazin der Universit{\"a}t Potsdam},
  number    = {01/2024},
  issn      = {2194-4245},
  doi       = {10.25932/publishup-63129},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-631291},
  pages     = {98},
  year      = {2024},
  abstract  = {Heute Morgen schon im Bett geswiped, geliked oder gepostet? Auf Arbeit an einer Video-Konferenz teilgenommen, eine Datenbank benutzt oder programmiert? Auf dem Heimweg schnell noch im Laden mit dem Smartphone bezahlt, Podcasts geh{\"o}rt und die Ausleihe der Bibliotheksb{\"u}cher verl{\"a}ngert? Und abends auf der Couch mit dem Tablet auf ELSTER.de die Steuererkl{\"a}rung ausgef{\"u}llt, online geshoppt oder Rechnungen bezahlt, ehe die Streaming-Plattform mit einer Serie lockt? Unser Leben ist durch und durch digitalisiert. Diese Ver{\"a}nderungen machen vieles schneller, leichter, effizienter. Doch damit Schritt zu halten, verlangt uns einiges ab und gelingt beileibe nicht allen. Es gibt Menschen, die f{\"u}r eine {\"U}berweisung lieber zur Bank gehen, das Programmieren den Experten {\"u}berlassen, die Steuererkl{\"a}rung per Post schicken und das Smartphone nur zum Telefonieren benutzen. Sie wollen nicht, vielleicht k{\"o}nnen sie auch nicht. Haben es nicht gelernt. Andere, j{\"u}ngere Menschen, wachsen als „Digital Natives" inmitten digitaler Ger{\"a}te, Tools und Prozesse auf. Aber k{\"o}nnen sie deshalb wirklich damit umgehen? Oder brauchen auch sie digitale Bildung? Aber wie sieht erfolgreiche digitale Bildung eigentlich aus? Lernen wir dabei ein Tablet zu bedienen, richtig zu googeln und Excel-Tabellen zu schreiben? M{\"o}glicherweise geht es um mehr: darum, den umfassenden Wandel zu verstehen, der unsere Welt erfasst, seitdem sie in Einsen und Nullen zerlegt und virtuell neu aufgebaut wird. Aber wie lernen wir, in einer Welt der Digitalit{\"a}t zu leben - mit allem, was dazu geh{\"o}rt und zu unserem Nutzen? F{\"u}r die aktuelle Ausgabe der „Portal Wissen" haben wir uns an der Universit{\"a}t Potsdam umgeschaut, welche Rolle die Verbindung von Digitalisierung und Lernen in der Forschung der verschiedenen Disziplinen spielt: Wir haben mit Katharina Scheiter, Professorin f{\"u}r digitale Bildung, {\"u}ber die Zukunft in deutschen Schulen gesprochen und uns gleich von mehreren Expert*innen Beispiele daf{\"u}r zeigen lassen, wie digitale Instrumente schulisches Lernen, aber auch Weiterbildung im Berufsleben verbessern k{\"o}nnen. Außerdem haben uns Forschende aus Informatik und Agrarforschung vorgef{\"u}hrt, wie auch gestandene Landwirte dank digitaler Hilfsmittel noch viel {\"u}ber ihr Land und ihre Arbeit lernen k{\"o}nnen. Wir haben mit Bildungsforschenden gesprochen, die mithilfe von Big Data analysieren, wie Jungen und M{\"a}dchen lernen und wo m{\"o}gliche Ursachen f{\"u}r Unterschiede zu suchen sind. Die Bildungsund Politikwissenschaftlerin Nina Kolleck wiederum schaut auf Bildung vor dem Hintergrund der Globalisierung und setzt dabei auf die Auswertung von großen Mengen Social-Media- Daten. Dabei verlieren wir nat{\"u}rlich die Vielfalt der Forschung an der Uni Potsdam nicht aus den Augen: Wir stellen der Strafrechtlerin Anna Albrecht 33 Fragen, begleiten eine Gruppe von Geoforschenden in den Himalaya und lassen uns erkl{\"a}ren, welche Alternativen es bald zu Antibiotika geben k{\"o}nnte. Außerdem geht es in diesem Magazin um Stress und wie er uns krankmacht, die Forschung zu nachhaltiger Erzgewinnung und neue Ans{\"a}tze in der Schulentwicklung. Neu ist auch eine ganze Reihe k{\"u}rzerer Beitr{\"a}ge, die zum Bl{\"a}ttern und Schm{\"o}kern einladen: von Forschungsnews und Personalia- Infos {\"u}ber fotografische Einblicke in Labore, einfache Erkl{\"a}rungen komplexer Ph{\"a}nomene und Ausblicke in die weite Forschungswelt bis hin zu einer kleinen Wissenschaftsutopie, einem pers{\"o}nlichen Dank an die Forschung und einem Wissenschaftscomic. All das im Namen der Bildung, versteht sich. Viel Vergn{\"u}gen bei der Lekt{\"u}re!},
  language  = {de}
}
@misc{PhuongHosseiniSandbergetal.2020,
  author    = {Phuong, Le Quang and Hosseini, Seyed Mehrdad and Sandberg, Oskar J. and Zou, Yingping and Woo, Han Young and Neher, Dieter and Shoaee, Safa},
  title     = {Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-57001},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-570018},
  pages     = {8},
  year      = {2020},
  abstract  = {The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.},
  language  = {en}
}
@misc{GarciaBenitoQuartiQuelozetal.2020,
  author    = {Garc{\´i}a-Benito, In{\´e}s and Quarti, Claudio and Queloz, Valentin I. E. and Hofstetter, Yvonne J. and Becker-Koch, David and Caprioglio, Pietro and Neher, Dieter and Orlandi, Simonetta and Cavazzini, Marco and Pozzi, Gianluca and Even, Jacky and Nazeeruddin, Mohammad Khaja and Vaynzof, Yana and Grancini, Giulia},
  title     = {Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-51242},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512420},
  pages     = {13},
  year      = {2020},
  abstract  = {Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.},
  language  = {en}
}
@article{GarciaBenitoQuartiQuelozetal.2020,
  author    = {Garc{\´i}a-Benito, In{\´e}s and Quarti, Claudio and Queloz, Valentin I. E. and Hofstetter, Yvonne J. and Becker-Koch, David and Caprioglio, Pietro and Neher, Dieter and Orlandi, Simonetta and Cavazzini, Marco and Pozzi, Gianluca and Even, Jacky and Nazeeruddin, Mohammad Khaja and Vaynzof, Yana and Grancini, Giulia},
  title     = {Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites},
  series = {Frontiers in Chemistry},
  volume    = {7},
  journal   = {Frontiers in Chemistry},
  publisher = {Frontiers Media},
  address   = {Lausanne},
  issn      = {2296-2646},
  doi       = {10.3389/fchem.2019.00946},
  pages     = {1 -- 11},
  year      = {2020},
  abstract  = {Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.},
  language  = {en}
}
@article{TokmoldinVollbrechtHosseinietal.2021,
  author    = {Tokmoldin, Nurlan and Vollbrecht, Joachim and Hosseini, Seyed Mehrdad and Sun, Bowen and Perdig{\´o}n-Toro, Lorena and Woo, Han Young and Zou, Yingping and Neher, Dieter and Shoaee, Safa},
  title     = {Explaining the fill-factor and photocurrent losses of nonfullerene acceptor-based solar cells by probing the long-range charge carrier diffusion and drift lengths},
  series = {Advanced energy materials},
  volume    = {11},
  journal   = {Advanced energy materials},
  number    = {22},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6840},
  doi       = {10.1002/aenm.202100804},
  pages     = {9},
  year      = {2021},
  abstract  = {Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80\% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as theta and alpha. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining theta and alpha in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices-including the high efficiency nonfullerene acceptor blends-and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.},
  language  = {en}
}
@misc{StolterfohtGrischekCaprioglioetal.2020,
  author    = {Stolterfoht, Martin and Grischek, Max and Caprioglio, Pietro and Wolff, Christian Michael and Gutierrez-Partida, Emilio and Pe{\~n}a-Camargo, Francisco and Rothhardt, Daniel and Zhang, Shanshan and Raoufi, Meysam and Wolansky, Jakob and Abdi-Jalebi, Mojtaba and Stranks, Samuel D. and Albrecht, Steve and Kirchartz, Thomas and Neher, Dieter},
  title     = {How to quantify the efficiency potential of neat perovskite films},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {17},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-51662},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-516622},
  pages     = {12},
  year      = {2020},
  abstract  = {Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell. By measuring the intensity dependence of the external open-circuit voltage and the internal quasi-Fermi level splitting (QFLS), the transport resistance-free efficiency of the complete cell as well as the efficiency potential of any neat perovskite film with or without attached transport layers are quantified. Moreover, intensity-dependent QFLS measurements on different perovskite compositions allows for disentangling of the impact of the interfaces and the perovskite surface on the non-radiative fill factor and open-circuit voltage loss. It is found that potassium-passivated triple cation perovskite films stand out by their exceptionally high implied PCEs > 28\%, which could be achieved with ideal transport layers. Finally, strategies are presented to reduce both the ideality factor and transport losses to push the efficiency to the thermodynamic limit.},
  language  = {en}
}