@article{YuanZhangQiuetal.2022,
  author    = {Yuan, Jun and Zhang, Chujun and Qiu, Beibei and Liu, Wei and So, Shu Kong and Mainville, Mathieu and Leclerc, Mario and Shoaee, Safa and Neher, Dieter and Zou, Yingping},
  title     = {Effects of energetic disorder in bulk heterojunction organic solar cells},
  series = {Energy \& environmental science},
  volume    = {15},
  journal   = {Energy \& environmental science},
  number    = {7},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1754-5692},
  doi       = {10.1039/d2ee00271j},
  pages     = {2806 -- 2818},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{YeZhangWarbyetal.2022,
  author    = {Ye, Fangyuan and Zhang, Shuo and Warby, Jonathan and Wu, Jiawei and Gutierrez-Partida, Emilio and Lang, Felix and Shah, Sahil and Saglamkaya, Elifnaz and Sun, Bowen and Zu, Fengshuo and Shoai, Safa and Wang, Haifeng and Stiller, Burkhard and Neher, Dieter and Zhu, Wei-Hong and Stolterfoht, Martin and Wu, Yongzhen},
  title     = {Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane},
  series = {Nature Communications},
  volume    = {13},
  journal   = {Nature Communications},
  publisher = {Springer Nature},
  address   = {London},
  issn      = {2041-1723},
  doi       = {10.1038/s41467-022-34203-x},
  pages     = {12},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{YeZhangWarbyetal.2022,
  author    = {Ye, Fangyuan and Zhang, Shuo and Warby, Jonathan and Wu, Jiawei and Gutierrez-Partida, Emilio and Lang, Felix and Shah, Sahil and Saglamkaya, Elifnaz and Sun, Bowen and Zu, Fengshuo and Shoaee, Safa and Wang, Haifeng and Stiller, Burkhard and Neher, Dieter and Zhu, Wei-Hong and Stolterfoht, Martin and Wu, Yongzhen},
  title     = {Overcoming C-60-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane},
  series = {Nature Communications},
  volume    = {13},
  journal   = {Nature Communications},
  number    = {1},
  publisher = {Nature Publishing Group},
  address   = {London},
  issn      = {2041-1723},
  doi       = {10.1038/s41467-022-34203-x},
  pages     = {12},
  year      = {2022},
  abstract  = {Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C-60 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/C-60 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 110mV, and retain >97\% of the initial efficiency after 400h 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. Effective transport layers are essential to suppress non-radiative recombination losses. Here, the authors introduce phenylamino-functionalized ortho-carborane as an interfacial layer, and realise inverted perovskite solar cells with efficiency of over 23\% and operational stability of T97=400h.},
  language  = {en}
}
@article{WarbyZuZeiskeetal.2022,
  author    = {Warby, Jonathan and Zu, Fengshuo and Zeiske, Stefan and Gutierrez-Partida, Emilio and Frohloff, Lennart and Kahmann, Simon and Frohna, Kyle and Mosconi, Edoardo and Radicchi, Eros and Lang, Felix and Shah, Sahil and Pena-Camargo, Francisco and Hempel, Hannes and Unold, Thomas and Koch, Norbert and Armin, Ardalan and De Angelis, Filippo and Stranks, Samuel D. and Neher, Dieter and Stolterfoht, Martin},
  title     = {Understanding performance limiting interfacial recombination in pin Perovskite solar cells},
  series = {Advanced energy materials},
  volume    = {12},
  journal   = {Advanced energy materials},
  number    = {12},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6832},
  doi       = {10.1002/aenm.202103567},
  pages     = {10},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{VollbrechtTokmoldinSunetal.2022,
  author    = {Vollbrecht, Joachim and Tokmoldin, Nurlan and Sun, Bowen and Brus, Viktor V. and Shoaee, Safa and Neher, Dieter},
  title     = {Determination of the charge carrier density in organic solar cells},
  series = {Journal of applied physics},
  volume    = {131},
  journal   = {Journal of applied physics},
  number    = {22},
  publisher = {American Institute of Physics},
  address   = {Melville, NY},
  issn      = {0021-8979},
  doi       = {10.1063/5.0094955},
  pages     = {18},
  year      = {2022},
  abstract  = {The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchers. Published under an exclusive license by AIP Publishing.},
  language  = {en}
}
@article{TockhornSutterCruzBournazouetal.2022,
  author    = {Tockhorn, Philipp and Sutter, Johannes and Cruz Bournazou, Alexandros and Wagner, Philipp and J{\"a}ger, Klaus and Yoo, Danbi and Lang, Felix and Grischek, Max and Li, Bor and Li, Jinzhao and Shargaieva, Oleksandra and Unger, Eva and Al-Ashouri, Amran and K{\"o}hnen, Eike and Stolterfoht, Martin and Neher, Dieter and Schlatmann, Rutger and Rech, Bernd and Stannowski, Bernd and Albrecht, Steve and Becker, Christiane},
  title     = {Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells},
  series = {Nature nanotechnology},
  volume    = {17},
  journal   = {Nature nanotechnology},
  number    = {11},
  publisher = {Nature Publishing Group},
  address   = {London [u.a.]},
  issn      = {1748-3387},
  doi       = {10.1038/s41565-022-01228-8},
  pages     = {1214 -- 1221},
  year      = {2022},
  abstract  = {Designing gentle sinusoidal nanotextures enables the realization of high-efficiency perovskite-silicon solar cells <br /> Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50\% to 95\%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80\%.},
  language  = {en}
}
@article{SunSandbergNeheretal.2022,
  author    = {Sun, Bowen and Sandberg, Oskar and Neher, Dieter and Armin, Ardalan and Shoaee, Safa},
  title     = {Wave optics of differential absorption spectroscopy in thick-junction organic solar cells},
  series = {Physical review applied / The American Physical Society},
  volume    = {17},
  journal   = {Physical review applied / The American Physical Society},
  number    = {5},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2331-7019},
  doi       = {10.1103/PhysRevApplied.17.054016},
  pages     = {12},
  year      = {2022},
  abstract  = {Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.},
  language  = {en}
}
@article{PoelkingBenduhnSpoltoreetal.2022,
  author    = {Poelking, Carl and Benduhn, Johannes and Spoltore, Donato and Schwarze, Martin and Roland, Steffen and Piersimoni, Fortunato and Neher, Dieter and Leo, Karl and Vandewal, Koen and Andrienko, Denis},
  title     = {Open-circuit voltage of organic solar cells},
  series = {Communications physics},
  volume    = {5},
  journal   = {Communications physics},
  number    = {1},
  publisher = {Nature portfolio},
  address   = {Berlin},
  issn      = {2399-3650},
  doi       = {10.1038/s42005-022-01084-x},
  pages     = {7},
  year      = {2022},
  abstract  = {Organic photovoltaics (PV) is an energy-harvesting technology that offers many advantages, such as flexibility, low weight and cost, as well as environmentally benign materials and manufacturing techniques. Despite growth of power conversion efficiencies to around 19 \% in the last years, organic PVs still lag behind inorganic PV technologies, mainly due to high losses in open-circuit voltage. Understanding and improving open circuit voltage in organic solar cells is challenging, as it is controlled by the properties of a donor-acceptor interface where the optical excitations are separated into charge carriers. Here, we provide an electrostatic model of a rough donor-acceptor interface and test it experimentally on small molecule PV materials systems. The model provides concise relationships between the open-circuit voltage, photovoltaic gap, charge-transfer state energy, and interfacial morphology. In particular, we show that the electrostatic bias generated across the interface reduces the photovoltaic gap. This negative influence on open-circuit voltage can, however, be circumvented by adjusting the morphology of the donor-acceptor interface. Organic solar cells, despite their high power conversion efficiencies, suffer from open circuit voltage losses making them less appealing in terms of applications. Here, the authors, supported with experimental data on small molecule photovoltaic cells, relate open circuit voltage to photovoltaic gap, charge-transfer state energy, and donor-acceptor interfacial morphology.},
  language  = {en}
}
@article{PerdigonToroLeQuangPhuongElleretal.2022,
  author    = {Perdig{\´o}n-Toro, Lorena and Le Quang Phuong, and Eller, Fabian and Freychet, Guillaume and Saglamkaya, Elifnaz and Khan, Jafar and Wei, Qingya and Zeiske, Stefan and Kroh, Daniel and Wedler, Stefan and Koehler, Anna and Armin, Ardalan and Laquai, Frederic and Herzig, Eva M. and Zou, Yingping and Shoaee, Safa and Neher, Dieter},
  title     = {Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages},
  series = {Advanced energy materials},
  volume    = {12},
  journal   = {Advanced energy materials},
  number    = {12},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6832},
  doi       = {10.1002/aenm.202103422},
  pages     = {13},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{PenaCamargoThiesbrummelHempeletal.2022,
  author    = {Pena-Camargo, Francisco and Thiesbrummel, Jarla and Hempel, Hannes and Musiienko, Artem and Le Corre, Vincent M. and Diekmann, Jonas and Warby, Jonathan and Unold, Thomas and Lang, Felix and Neher, Dieter and Stolterfoht, Martin},
  title     = {Revealing the doping density in perovskite solar cells and its impact on device performance},
  series = {Applied physics reviews},
  volume    = {9},
  journal   = {Applied physics reviews},
  number    = {2},
  publisher = {AIP Publishing},
  address   = {Melville},
  issn      = {1931-9401},
  doi       = {10.1063/5.0085286},
  pages     = {11},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{NeusserSunTanetal.2022,
  author    = {Neusser, David and Sun, Bowen and Tan, Wen Liang and Thomsen, Lars and Schultz, Thorsten and Perdigon-Toro, Lorena and Koch, Norbert and Shoaee, Safa and McNeill, Christopher R. and Neher, Dieter and Ludwigs, Sabine},
  title     = {Spectroelectrochemically determined energy levels of PM6:Y6 blends and their relevance to solar cell performance},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {10},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {32},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7526},
  doi       = {10.1039/d2tc01918c},
  pages     = {11565 -- 11578},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{LeCorreDiekmannPenaCamargoetal.2022,
  author    = {Le Corre, Vincent M. and Diekmann, Jonas and Pe{\~n}a-Camargo, Francisco and Thiesbrummel, Jarla and Tokmoldin, Nurlan and Gutierrez-Partida, Emilio and Peters, Karol Pawel and Perdig{\´o}n-Toro, Lorena and Futscher, Moritz H. and Lang, Felix and Warby, Jonathan and Snaith, Henry J. and Neher, Dieter and Stolterfoht, Martin},
  title     = {Quantification of efficiency losses due to mobile ions in Perovskite solar cells via fast hysteresis measurements},
  series = {Solar RRL},
  volume    = {6},
  journal   = {Solar RRL},
  number    = {4},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2367-198X},
  doi       = {10.1002/solr.202100772},
  pages     = {10},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{KrohEllerSchoetzetal.2022,
  author    = {Kroh, Daniel and Eller, Fabian and Sch{\"o}tz, Konstantin and Wedler, Stefan and Perdig{\´o}n-Toro, Lorena and Freychet, Guillaume and Wei, Qingya and D{\"o}rr, Maximilian and Jones, David and Zou, Yingping and Herzig, Eva M. and Neher, Dieter and K{\"o}hler, Anna},
  title     = {Identifying the signatures of intermolecular interactions in blends of PM6 with Y6 and N4 using absorption spectroscopy},
  series = {Advanced functional materials},
  volume    = {32},
  journal   = {Advanced functional materials},
  number    = {44},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1616-301X},
  doi       = {10.1002/adfm.202205711},
  pages     = {14},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{GrischekCaprioglioZhangetal.2022,
  author    = {Grischek, Max and Caprioglio, Pietro and Zhang, Jiahuan and Pena-Camargo, Francisco and Sveinbjornsson, Kari and Zu, Fengshuo and Menzel, Dorothee and Warby, Jonathan and Li, Jinzhao and Koch, Norbert and Unger, Eva and Korte, Lars and Neher, Dieter and Stolterfoht, Martin and Albrecht, Steve},
  title     = {Efficiency Potential and Voltage Loss of Inorganic CsPbI2Br Perovskite Solar Cells},
  series = {Solar RRL},
  volume    = {6},
  journal   = {Solar RRL},
  number    = {11},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2367-198X},
  doi       = {10.1002/solr.202200690},
  pages     = {12},
  year      = {2022},
  abstract  = {Inorganic perovskite solar cells show excellent thermal stability, but the reported power conversion efficiencies are still lower than for organic-inorganic perovskites. This is mainly caused by lower open-circuit voltages (V(OC)s). Herein, the reasons for the low V-OC in inorganic CsPbI2Br perovskite solar cells are investigated. Intensity-dependent photoluminescence measurements for different layer stacks reveal that n-i-p and p-i-n CsPbI2Br solar cells exhibit a strong mismatch between quasi-Fermi level splitting (QFLS) and V-OC. Specifically, the CsPbI2Br p-i-n perovskite solar cell has a QFLS-e center dot V-OC mismatch of 179 meV, compared with 11 meV for a reference cell with an organic-inorganic perovskite of similar bandgap. On the other hand, this study shows that the CsPbI2Br films with a bandgap of 1.9 eV have a very low defect density, resulting in an efficiency potential of 20.3\% with a MeO-2PACz hole-transporting layer and 20.8\% on compact TiO2. Using ultraviolet photoelectron spectroscopy measurements, energy level misalignment is identified as a possible reason for the QFLS-e center dot V-OC mismatch and strategies for overcoming this V-OC limitation are discussed. This work highlights the need to control the interfacial energetics in inorganic perovskite solar cells, but also gives promise for high efficiencies once this issue is resolved.},
  language  = {en}
}
@article{FritschKurpiersRolandetal.2022,
  author    = {Fritsch, Tobias and Kurpiers, Jona and Roland, Steffen and Tokmoldin, Nurlan and Shoaee, Safa and Ferron, Thomas and Collins, Brian A. and Janietz, Silvia and Vandewal, Koen and Neher, Dieter},
  title     = {On the interplay between CT and singlet exciton emission in organic solar cells with small driving force and its impact on voltage loss},
  series = {Advanced energy materials},
  volume    = {12},
  journal   = {Advanced energy materials},
  number    = {31},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6832},
  doi       = {10.1002/aenm.202200641},
  pages     = {11},
  year      = {2022},
  abstract  = {The interplay between free charge carriers, charge transfer (CT) states and singlet excitons (S-1) determines the recombination pathway and the resulting open circuit voltage (V-OC) of organic solar cells. By combining a well-aggregated low bandgap polymer with different blend ratios of the fullerenes PCBM and ICBA, the energy of the CT state (E-CT) is varied by 130 meV while leaving the S-1 energy of the polymer (ES1\[{E_{{{\rm{S}}_1}}}\]) unaffected. It is found that the polymer exciton dominates the radiative properties of the blend when ECT\[{E_{{\rm{CT}}}}\] approaches ES1\[{E_{{{\rm{S}}_1}}}\], while the V-OC remains limited by the non-radiative decay of the CT state. It is concluded that an increasing strength of the exciton in the optical spectra of organic solar cells will generally decrease the non-radiative voltage loss because it lowers the radiative V-OC limit (V-OC,V-rad), but not because it is more emissive. The analysis further suggests that electronic coupling between the CT state and the S-1 will not improve the V-OC, but rather reduce the V-OC,V-rad. It is anticipated that only at very low CT state absorption combined with a fairly high CT radiative efficiency the solar cell benefit from the radiative properties of the singlet excitons.},
  language  = {en}
}
@article{BrinkmannBeckerZimmermannetal.2022,
  author    = {Brinkmann, Kai Oliver and Becker, Tim and Zimmermann, Florian and Kreusel, Cedric and Gahlmann, Tobias and Theisen, Manuel and Haeger, Tobias and Olthof, Selina and T{\"u}ckmantel, Christian and G{\"u}nster, M. and Maschwitz, Timo and G{\"o}belsmann, Fabian and Koch, Christine and Hertel, Dirk and Caprioglio, Pietro and Pe{\~n}a-Camargo, Francisco and Perdig{\´o}n-Toro, Lorena and Al-Ashouri, Amran and Merten, Lena and Hinderhofer, Alexander and Gomell, Leonie and Zhang, Siyuan and Schreiber, Frank and Albrecht, Steve and Meerholz, Klaus and Neher, Dieter and Stolterfoht, Martin and Riedl, Thomas},
  title     = {Perovskite-organic tandem solar cells with indium oxide interconnect},
  series = {Nature},
  volume    = {604},
  journal   = {Nature},
  number    = {7905},
  publisher = {Nature Research},
  address   = {Berlin},
  issn      = {0028-0836},
  doi       = {10.1038/s41586-022-04455-0},
  pages     = {280 -- 286},
  year      = {2022},
  abstract  = {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).},
  language  = {en}
}