@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
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{JoštAlbrechtKegelmannetal.2017, author = {Jošt, Marko and Albrecht, Steve and Kegelmann, Lukas and Wolff, Christian Michael and Lang, Felix and Lipovšek, Benjamin and Krč, Janez and Korte, Lars and Neher, Dieter and Rech, Bernd and Topič, Marko}, title = {Efficient light management by textured nanoimprinted layers for perovskite solar cells}, series = {ACS photonics}, volume = {4}, journal = {ACS photonics}, publisher = {American Chemical Society}, address = {Washington}, issn = {2330-4022}, doi = {10.1021/acsphotonics.7b00138}, pages = {1232 -- 1239}, year = {2017}, abstract = {Inorganic-organic perovskites like methylammonium-lead-iodide have proven to be an effective class of 17 materials for fabricating efficient solar cells. To improve their performance, light management techniques using textured surfaces, similar to those used in established solar cell technologies, should be considered. Here, we apply a light management foil created by UV nanoimprint lithography on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3\% efficiency. The obtained 1 mA cm(-2) increase in the short-circuit current density translates to a relative improvement in cell performance of 5\%, which results in a power conversion efficiency of 17.1\%. Optical 3D simulations based on experimentally obtained parameters were used to support the experimental findings. A good match between the simulated and experimental data was obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current density of up to 10\% is possible for large-area devices. Therefore, our results present the potential of light management foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in the field of perovskite solar cells.}, language = {en} } @article{BraungerMundtWolffetal.2018, author = {Braunger, Steffen and Mundt, Laura E. and Wolff, Christian Michael and Mews, Mathias and Rehermann, Carolin and Jost, Marko and Tejada, Alvaro and Eisenhauer, David and Becker, Christiane and Andres Guerra, Jorge and Unger, Eva and Korte, Lars and Neher, Dieter and Schubert, Martin C. and Rech, Bernd and Albrecht, Steve}, title = {Cs(x)FA(1-x)Pb(l(1-y)Br(y))(3) Perovskite Compositions}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {122}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {30}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b06459}, pages = {17123 -- 17135}, year = {2018}, abstract = {We report on the formation of wrinkle-patterned surface morphologies in cesium formamidinium-based Cs(x)FA(1-y)Pb(I1-yBry)(3) perovskite compositions with x = 0-0.3 and y = 0-0.3 under various spin-coating conditions. By varying the Cs and Br contents, the perovskite precursor solution concentration and the spin-coating procedure, the occurrence and characteristics of the wrinkle-shaped morphology can be tailored systematically. Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3) perovskite layers were analyzed regarding their surface roughness, microscopic structure, local and overall composition, and optoelectronic properties. Application of these films in p-i-n perovskite solar cells (PSCs) with indium-doped tin oxide/NiOx/perovskite/C-60/bathocuproine/Cu architecture resulted in up to 15.3 and 17.0\% power conversion efficiency for the flat and wrinkled morphology, respectively. Interestingly, we find slightly red-shifted photoluminescence (PL) peaks for wrinkled areas and we are able to directly correlate surface topography with PL peak mapping. This is attributed to differences in the local grain size, whereas there is no indication for compositional demixing in the films. We show that the perovskite composition, crystallization kinetics, and layer thickness strongly influence the formation of wrinkles which is proposed to be related to the release of compressive strain during perovskite crystallization. Our work helps us to better understand film formation and to further improve the efficiency of PSCs with widely used mixed-perovskite compositions.}, language = {en} } @article{CaprioglioZuWolffetal.2019, author = {Caprioglio, Pietro and Zu, Fengshuo and Wolff, Christian Michael and Prieto, Jose A. Marquez and Stolterfoht, Martin and Becker, Pascal and Koch, Norbert and Unold, Thomas and Rech, Bernd and Albrecht, Steve and Neher, Dieter}, title = {High open circuit voltages in pin-type perovskite solar cells through strontium addition}, series = {Sustainable Energy \& Fuels}, volume = {3}, journal = {Sustainable Energy \& Fuels}, number = {2}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2398-4902}, doi = {10.1039/c8se00509e}, pages = {550 -- 563}, year = {2019}, abstract = {The incorporation of even small amounts of strontium (Sr) into lead-base hybrid quadruple cation perovskite solar cells results in a systematic increase of the open circuit voltage (V-oc) in pin-type perovskite solar cells. We demonstrate via absolute and transient photoluminescence (PL) experiments how the incorporation of Sr significantly reduces the non-radiative recombination losses in the neat perovskite layer. We show that Sr segregates at the perovskite surface, where it induces important changes of morphology and energetics. Notably, the Sr-enriched surface exhibits a wider band gap and a more n-type character, accompanied with significantly stronger surface band bending. As a result, we observe a significant increase of the quasi-Fermi level splitting in the neat perovskite by reduced surface recombination and more importantly, a strong reduction of losses attributed to non-radiative recombination at the interface to the C-60 electron-transporting layer. The resulting solar cells exhibited a V-oc of 1.18 V, which could be further improved to nearly 1.23 V through addition of a thin polymer interlayer, reducing the non-radiative voltage loss to only 110 meV. Our work shows that simply adding a small amount of Sr to the precursor solutions induces a beneficial surface modification in the perovskite, without requiring any post treatment, resulting in high efficiency solar cells with power conversion efficiency (PCE) up to 20.3\%. Our results demonstrate very high V-oc values and efficiencies in Sr-containing quadruple cation perovskite pin-type solar cells and highlight the imperative importance of addressing and minimizing the recombination losses at the interface between perovskite and charge transporting layer.}, language = {en} } @article{KegelmannTockhornWolffetal.2019, author = {Kegelmann, Lukas and Tockhorn, Philipp and Wolff, Christian Michael and M{\´a}rquez, Jos{\´e} A. and Caicedo D{\´a}vila, Sebasti{\´a}n and Korte, Lars and Unold, Thomas and Loevenich, Wilfried and Neher, Dieter and Rech, Bernd and Albrecht, Steve}, title = {Mixtures of Dopant-Free Spiro-OMeTAD and Water-Free PEDOT as a Passivating Hole Contact in Perovskite Solar Cells}, series = {ACS applied materials \& interfaces}, volume = {11}, journal = {ACS applied materials \& interfaces}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.9b01332}, pages = {9172 -- 9181}, year = {2019}, abstract = {Doped spiro-OMeTAD at present is the most commonly used hole transport material (HTM) in n-i-p-type perovskite solar cells, enabling high efficiencies around 22\%. However, the required dopants were shown to induce nonradiative recombination of charge carriers and foster degradation of the solar cell. Here, in a novel approach, highly conductive and inexpensive water-free poly(3,4-ethylenedioxythiophene) (PEDOT) is used to replace these dopants. The resulting spiro-OMeTAD/PEDOT (SpiDOT) mixed films achieve higher lateral conductivities than layers of doped spiro-OMeTAD. Furthermore, combined transient and steady-state photoluminescence studies reveal a passivating effect of PEDOT, suppressing nonradiative recombination losses at the perovskite/HTM interface. This enables excellent quasi-Fermi level splitting values of up to 1.24 eV in perovskite/SpiDOT layer stacks and high open-circuit voltages (V-OC) up to 1.19 V in complete solar cells. Increasing the amount of dopant-free spiro-OMeTAD in SpiDOT layers is shown to enhance hole extraction and thereby improves the fill factor in solar cells. As a consequence, stabilized efficiencies up to 18.7\% are realized, exceeding cells with doped spiro-OMeTAD as a HTM in this study. Moreover, to the best of our knowledge, these results mark the lowest nonradiative recombination loss in the V-OC (140 mV with respect to the Shockley-Queisser limit) and highest efficiency reported so far for perovskite solar cells using PEDOT as a HTM.}, language = {en} } @article{CaprioglioStolterfohtWolffetal.2019, author = {Caprioglio, Pietro and Stolterfoht, Martin and Wolff, Christian Michael and Unold, Thomas and Rech, Bernd and Albrecht, Steve and Neher, Dieter}, title = {On the relation between the open-circuit voltage and quasi-fermi level splitting in efficient perovskite solar cells}, series = {advanced energy materials}, volume = {9}, journal = {advanced energy materials}, number = {33}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201901631}, pages = {10}, year = {2019}, abstract = {Today's perovskite solar cells (PSCs) are limited mainly by their open-circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity-dependent measurements of the quasi-Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin-type PSCs with efficiencies above 20\%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley-Queisser theory. This has far-reaching implications for the applicability of some well-established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift-diffusion simulations, the intensity dependence of the QFLS, the QFLS-VOC offset and the ideality factor are consistently explained by trap-assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS-VOC relation is of great importance.}, language = {en} } @article{KegelmannWolffAwinoetal.2017, author = {Kegelmann, Lukas and Wolff, Christian Michael and Awino, Celline and Lang, Felix and Unger, Eva L. and Korte, Lars and Dittrich, Thomas and Neher, Dieter and Rech, Bernd and Albrecht, Steve}, title = {It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis}, series = {ACS applied materials \& interfaces}, volume = {9}, journal = {ACS applied materials \& interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.7b00900}, pages = {17246 -- 17256}, year = {2017}, abstract = {Solar cells made from inorganic organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 degrees C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C-60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop, the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0\%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.}, language = {en} } @article{RolandNeubertAlbrechtetal.2015, author = {Roland, Steffen and Neubert, Sebastian and Albrecht, Steve and Stannowski, Bernd and Seger, Mark and Facchetti, Antonio and Schlatmann, Rutger and Rech, Bernd and Neher, Dieter}, title = {Hybrid Organic/Inorganic Thin-Film Multijunction Solar Cells Exceeding 11\% Power Conversion Efficiency}, series = {Advanced materials}, volume = {27}, journal = {Advanced materials}, number = {7}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201404698}, pages = {1262 -- 1267}, year = {2015}, abstract = {Hybrid multijunction solar cells comprising hydrogenated amorphous silicon and an organic bulk heterojunction are presented, reaching 11.7\% power conversion efficiency. The benefits of merging inorganic and organic subcells are pointed out, the optimization of the cells, including optical modeling predictions and tuning of the recombination contact are described, and an outlook of this technique is given.}, language = {en} }