With the emergence of highly efficient perovskite solar cells in both single‐ and multijunction architectures, there is an abundance of reports of extremely high external quantum efficiencies (EQE) up to 98%. Typically, the spectral maximum of the EQE is found in the range between 400 and 500 nm, which is even more surprising, as the transmittance of typically used indium tin oxide (ITO)/glass substrates does not exceed 90% in this wavelength range. Herein, the root cause of the high EQE values by a combination of experimental data and optical simulations is analyzed and explained. It is shown that the high refractive index of the perovskite absorber is strongly increasing the transmittance of incident light into the active perovskite layer, while the spectral distribution and ultimately the spectral position of the peak in the transmittance spectrum are strongly affected by the thickness and optical properties of the underlying transparent electrode.

Multi-junction solar cells provide an avenue to overcome fundamental efficiency limits of single-junction devices. The facile bandgap tunability of metal-halide perovskite solar cells renders them attractive building blocks for multi-junction architectures. Combinations with crystalline silicon and copper indium gallium selenide (CIGS) cells have been reported. All-perovskite tandem cells have likewise shown promising results. Meanwhile, narrow-gap non-fullerene acceptors (NFA) have revived the area of organic solar cells (OSCs) and unlocked skyrocketing efficiencies. Organic and perovskite semiconductors share similar processing technologies, which renders them attractive partners in multi junction architectures. As of yet, perovskite/organic tandem cells show subpar efficiencies of 20 per cent, limited by the low open circuit voltage (Voc) of wide-gap perovskite cells and losses introduced by the interconnect between the sub-cells. Here, we demonstrate two-terminal p-i-n perovskite/organic tandem cells with an efficiency of 23.5 per cent and a high Voc of 2.15 volts, operating near the levels predicted by a semi-empirical model. The perovskite sub-cells with optimized charge extraction layers afford an unsurpassed combination of a high Voc and fill-factor. The organic back-cells provide a high external quantum efficiency in the near-infrared. In surprising contrast to paradigmatic concerns about limited photostability of non-fullerene cells, we evidence an outstanding operational stability if excitons are predominantly generated on the NFA, which is the case in a tandem cell, where the illumination is spectrally filtered by the perovskite cell. A novel interconnect based on an ultra-thin (1.5 nanometers) metal like indium oxide layer offers unprecedented low optical/electrical losses. This work sets a new milestone for perovskite/organic tandem devices, that outperform the best p-i-n perovskite single junctions and are at par with perovskite/CIGS and all-perovskite multi-junctions. Perovskite/organic tandem architectures bear a realistic potential to reach an efficiency above 31%.

Several applications of perovskite solar cells (PSCs) demand a semitransparent top electrode to afford top‐illumination or see‐through devices. Transparent conductive oxides, such as indium tin oxide (ITO), typically require postdeposition annealing at elevated temperatures, which would thermally decompose the perovskite. In contrast, silver nanowires (AgNWs) in dispersions of water would be a very attractive alternative that can be deposited at ambient conditions. Water is environmentally friendly without safety concerns associated with alcohols, such as flammability. Due to the notorious moisture sensitivity of lead‐halide perovskites, aqueous processing of functional layers, such as electrodes, on top of a perovskite device stack is elusive. Here, impermeable electron transport layers (ETLs) are shown to enable the deposition of semitransparent AgNW electrodes from green aqueous dispersions on top of the perovskite cell without damage. The polyvinylpyrrolidone (PVP) capping agent of the AgNWs is found to cause a work–function shift and an energy barrier between the AgNWs and the adjacent ETL. Thus, a high carrier density (≈10 18 cm −3 ) in the ETL is required to achieve well‐behaved J/V characteristics free of s‐shapes. Ultimately, semitransparent PSCs are demonstrated that provide an efficiency of 17.4%, which is the highest efficiency of semitransparent p‐i‐n perovskite solar cells with an AgNW top electrode.

Aqueous dispersions of silver nanowires state an environmentally friendly avenue for highly conductive, yet transparent top electrodes for semi-transparent perovskite solar cells. However, for the well-known chemical instability of halide perovskites upon exposure to water, there are no reports of successful aqueous processing on top of perovskite devices. Here, we show that electron extraction layers of AZO/SnOx [1,2], with the SnOx grown by low temperature atomic layer deposition, provide outstanding protection layers, which even afford the spray coating of AgNW electrodes (sheet resistance Rsh =15 Ohm/sq and a transmittance of 90%) from water-based dispersions without damage to the perovskite. The layer sequence of the inverted cells is ITO/PTAA/perovskite/PCBM/AZO/SnOx/top-electrode. In devices without the ALD SnOx, aqueous spray processing decomposes the perovskite layers. Interestingly, the direct interface of Ag-NW/SnOx comprises a Schottky barrier, with characteristics strongly dependent on the charge carrier density of the SnOx. For a carrier density below 10^18 cm^-3, S-shaped J-V characteristics are found, that successively vanish upon UV-light soaking. For our low-T SnOx with 10^16 cm^-3, the insertion of a thin interfacial layer with a high charge carrier density (10^20 cm^-3), e.g. 10nm of ITO, is found to afford high performance semitransparent PSCs with an efficiency of 15%. Most importantly, compared to ITO electrodes Ag-NW based electrodes provide a key to achieve a higher transmittance in the IR, which is desirable for tandem Si/PSCs. [1] K. Brinkmann et al., Nat. Commun. 8, 13938 (2017). [2] L. Hoffmann et al. ACS Applied Mater. & Interfaces 10, 6006 (2018).

Tin oxide nanoparticles are employed as an electron transporting layer in solution‐processed polymer solar cells. Tin oxide based devices yield excellent performance and can interchangeably be used in conventional and inverted device configurations. In combination with poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer, tin oxide forms an effective interconnecting layer (ICL) for tandem solar cells. Conventional and inverted tandem cells with this ICL provide efficiencies up to 10.4% in good agreement with optical‐electrical modeling simulations. The critical advantage of tin oxide in an ICL in a conventional tandem structure over the commonly used zinc oxide is that the latter requires the use of a pH‐neutral formulation of PEDOT:PSS to fabricate the ICL, limiting the open‐circuit voltage (VOC) because of its low work function. The SnO2/PEDOT:PSS ICL, on the other hand, provides a nearly loss‐free VOC.

Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub‐cells, a proper interconnect is essential. This study demonstrates a novel all‐oxide interconnect based on the interface of the high‐work‐function (WF) metal oxide MoOx and low‐WF tin oxide (SnOx). In contrast to typical p‐/n‐type tunnel junctions, both the oxides are n‐type semiconductors with a WF of 5.2 and 4.2 eV, respectively. It is demonstrated that the electronic line‐up at the interface of MoOx and SnOx comprises a large intrinsic interface dipole (≈0.8 eV), which is key to afford ideal alignment of the conduction band of MoOx and SnOx, without the requirement of an additional metal or organic dipole layer. The presented MoOx/SnOx interconnect allows for the ideal (loss‐free) addition of the open circuit voltages of the two sub‐cells.

Despite the notable success of hybrid halide perovskite-based solar cells, their long-term stability is still a key-issue. Aside from optimizing the photoactive perovskite, the cell design states a powerful lever to improve stability under various stress conditions. Dedicated electrically conductive diffusion barriers inside the cell stack, that counteract the ingress of moisture and prevent the migration of corrosive halogen species, can substantially improve ambient and thermal stability. Although atomic layer deposition (ALD) is excellently suited to prepare such functional layers, ALD suffers from the requirement of vacuum and only allows for a very limited throughput. Here, we demonstrate for the first time spatial ALD-grown SnOx at atmospheric pressure as impermeable electron extraction layers for perovskite solar cells. We achieve optical transmittance and electrical conductivity similar to those in SnOx grown by conventional vacuum-based ALD. A low deposition temperature of 80 °C and a high substrate speed of 2.4 m min-1 yield SnOx layers with a low water vapor transmission rate of ∼10-4 gm-2 day-1 (at 60 °C/60% RH). Thereby, in perovskite solar cells, dense hybrid Al:ZnO/SnOx electron extraction layers are created that are the key for stable cell characteristics beyond 1000 h in ambient air and over 3000 h at 60 °C. Most notably, our work of introducing spatial ALD at atmospheric pressure paves the way to the future roll-to-roll manufacturing of stable perovskite solar cells.

Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnOx) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnOx/Ag or Cu/SnOx), in which the metal is efficiently protected against corrosion. Simultaneously, SnOx functions as an electron extraction layer. We unravel the spontaneous formation of a PbI2 interfacial layer between SnOx and the CH3NH3PbI3 perovskite. An interface dipole between SnOx and this PbI2 layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnOx. An electron extraction barrier between perovskite and PbI2 is identified, which is the lowest in devices based on SnOx grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.

Perovskite solar cells (PSCs) suffer from decomposition of the active material in the presence of moisture or heat. In addition, the corrosion of metal electrodes due to halide species needs to be overcome.[1,2] Here, we introduce ALD-grown tin oxide (SnOx) as impermeable electron extraction layer (EEL), which affords air resilient and temperature stable MAPbI3 PSCs. Being conductive, SnOx is positioned between the metal electrode and the perovskite. Its outstanding permeation barrier properties protect the perovskite against ingress of moisture or migrating metal atoms, while simultaneously the metal electrode is protected against leaking halide compounds.[2] Therefore, SnOx is also excellently suited to sandwich and protect ultra-thin metal layers (Ag or Cu) as cost efficient Indium-free semitransparent electrodes (SnOx/metal/SnOx) in PSCs. Using photoelectron spectroscopy, we unravel the formation of a PbI2 interfacial layer between a SnOx EEL and the perovskite. The resulting interface dipole between SnOx and the PbI2 depends on the choice of oxidant for ALD (water, ozone, oxygen plasma). SnOx grown by using ozone affords hysteresis-free devices with a stable efficiency of 16.3% and a remarkably high open circuit voltage of 1.17 V.[3] Finally, we fabricated semitransparent PSCs with efficiency >11% (Tvis = 17%) and an astonishing stability > 4500h under ambient conditions (>50% RH) or elevated temperatures (60°C).[4] [1] Y. Kato et al., Adv. Mater. Interf. 2015, 2, 150019 [2] K. Brinkmann et al., Nat. Commun. 8, 13938 [3] T. Hu et al. Adv. Mat. (submitted) [4] J. Zhao et al. Adv. Energ. Mat. (in press)

Advanced Energy MaterialsVolume 6, Issue 15 1600347 Communication Avoiding Photoinduced Shunts in Organic Solar Cells by the Use of Tin Oxide (SnOx) as Electron Extraction Material Instead of ZnO Sara Trost, Sara Trost Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorTim Becker, Tim Becker Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorAndreas Polywka, Andreas Polywka Chair of Large Area Optoelectronics, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorPatrick Görrn, Patrick Görrn Chair of Large Area Optoelectronics, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorMarek F. Oszajca, Marek F. Oszajca Nanograde AG, Laubisrütistrasse 50, 8712 Stäfa, SwitzerlandSearch for more papers by this authorNorman A. Luechinger, Norman A. Luechinger Nanograde AG, Laubisrütistrasse 50, 8712 Stäfa, SwitzerlandSearch for more papers by this authorDetlef Rogalla, Detlef Rogalla RUBION, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, GermanySearch for more papers by this authorMirko Weidner, Mirko Weidner Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorPhilip Reckers, Philip Reckers Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorThomas Mayer, Thomas Mayer Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorThomas Riedl, Corresponding Author Thomas Riedl Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanyE-mail: t.riedl@uni-wuppertal.deSearch for more papers by this author Sara Trost, Sara Trost Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorTim Becker, Tim Becker Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorAndreas Polywka, Andreas Polywka Chair of Large Area Optoelectronics, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorPatrick Görrn, Patrick Görrn Chair of Large Area Optoelectronics, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanySearch for more papers by this authorMarek F. Oszajca, Marek F. Oszajca Nanograde AG, Laubisrütistrasse 50, 8712 Stäfa, SwitzerlandSearch for more papers by this authorNorman A. Luechinger, Norman A. Luechinger Nanograde AG, Laubisrütistrasse 50, 8712 Stäfa, SwitzerlandSearch for more papers by this authorDetlef Rogalla, Detlef Rogalla RUBION, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, GermanySearch for more papers by this authorMirko Weidner, Mirko Weidner Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorPhilip Reckers, Philip Reckers Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorThomas Mayer, Thomas Mayer Surface Science Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstraße 32, 64287 Darmstadt, GermanySearch for more papers by this authorThomas Riedl, Corresponding Author Thomas Riedl Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, GermanyE-mail: t.riedl@uni-wuppertal.deSearch for more papers by this author First published: 02 June 2016 https://doi.org/10.1002/aenm.201600347Citations: 54Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Organic solar cells using zinc oxide (ZnO) based electron extraction layers (EELs) show a lowered shunt resistance along with a decay of the filling factor and open circuit voltage upon UV illumination, due to a loss of electron selectivity of the EEL. This issue is overcome by tin oxide (SnOx) as EEL, with a surface electronic structure different from ZnO. Citing Literature Supporting Information As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Filename Description aenm201600347-sup-0001-S1.pdf380.3 KB Supplementary Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume6, Issue15August 10, 20161600347 RelatedInformation

Transparent and electrically conductive gas diffusion barriers are reported. Tin oxide (SnOx ) thin films grown by atomic layer deposition afford extremely low water vapor transmission rates (WVTR) on the order of 10(-6) g (m(2) day)(-1) , six orders of magnitude better than that established with ITO layers. The electrical conductivity of SnOx remains high under damp heat conditions (85 °C/85% relative humidity (RH)), while that of ZnO quickly degrades by more than five orders of magnitude.

In organic solar cells (OSCs), the necessity of UV activation that comes with the use of ZnO- and TiOx-based electron extraction layers (EELs) can be avoided by using tin oxide (SnOx), which can be prepared at temperatures as low as 80 °C. In contrast to devices based on TiOx and ZnO, OSCs comprising SnOx as the EEL show well-behaved solar cell characteristics with a high fill factor (FF) and high efficiency, even without the UV spectral range of the AM1.5 solar spectrum.