Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells

Metal halide perovskites have attracted tremendous attention due to their excellent electronic properties. Recent advancements in device performance and stability of perovskite solar cells (PSCs) have been achieved with the application of self-assembled monolayers (SAMs), serving as stand-alone hole transport layers in the p-i-n architecture. Specifically, phosphonic acid SAMs, directly functionalizing indium-tin oxide (ITO), are presently adopted for highly efficient devices. Despite their successes, so far, little is known about the surface coverage of SAMs on ITO used in PSCs application, which can affect the device performance, as non-covered areas can result in shunting or low open-circuit voltage. In this study, we investigate the surface coverage of SAMs on ITO and observe that the SAM of MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid) inhomogeneously covers the ITO substrate. Instead, when adopting an intermediate layer of NiO between ITO and the SAM, the homogeneity, and hence the surface coverage of the SAM, improve. In this work, NiO is processed by plasma-assisted atomic layer deposition (ALD) with Ni(MeCp)2 as the precursor and O2 plasma as the co-reactant. Specifically, the presence of ALD NiO leads to a homogeneous distribution of SAM molecules on the metal oxide area, accompanied by a high shunt resistance in the devices with respect to those with SAM directly processed on ITO. At the same time, the SAM is key to the improvement of the open-circuit voltage of NiO + MeO-2PACz devices compared to those with NiO alone. Thus, the combination of NiO and SAM results in a narrower distribution of device performance reaching a more than 20% efficient champion device. The enhancement of SAM coverage in the presence of NiO is corroborated by several characterization techniques including advanced imaging by transmission electron microscopy (TEM), elemental composition quantification by Rutherford backscattering spectrometry (RBS), and conductive atomic force microscopy (c-AFM) mapping. We believe this finding will further promote the usage of phosphonic acid based SAM molecules in perovskite PV. </p

Resolving electron and hole transport properties in semiconductor materials by constant light-induced magneto transport

The knowledge of minority and majority charge carrier properties enables controlling the performance of solar cells, transistors, detectors, sensors, and LEDs. Here, we developed the constant light induced magneto transport method which resolves electron and hole mobility, lifetime, diffusion coefficient and length, and quasi-Fermi level splitting. We demonstrate the implication of the constant light induced magneto transport for silicon and metal halide perovskite films. We resolve the transport properties of electrons and holes predicting the material’s effectiveness for solar cell application without making the full device. The accessibility of fourteen material parameters paves the way for in-depth exploration of causal mechanisms limiting the efficiency and functionality of material structures. To demonstrate broad applicability, we further characterized twelve materials with drift mobilities spanning from 10–3 to 103 cm2V–1s–1 and lifetimes varying between 10–9 and 10–3 seconds. The universality of our method its potential to advance optoelectronic devices in various technological fields

Proton‐Radiation Tolerant All‐Perovskite Multijunction Solar Cells

Funder: European Research Council; Id: http://dx.doi.org/10.13039/501100000781Funder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266Funder: European Union's Horizon 2020Abstract: Radiation‐resistant but cost‐efficient, flexible, and ultralight solar sheets with high specific power (W g−1) are the “holy grail” of the new space revolution, powering private space exploration, low‐cost missions, and future habitats on Moon and Mars. Herein, this study investigates an all‐perovskite tandem photovoltaic (PV) technology that uses an ultrathin active layer (1.56 µm) but offers high power conversion efficiency, and discusses its potential for high‐specific‐power applications. This study demonstrates that all‐perovskite tandems possess a high tolerance to the harsh radiation environment in space. The tests under 68 MeV proton irradiation show negligible degradation (22%. Using high spatial resolution photoluminescence (PL) microscopy, it is revealed that defect clusters in GaAs are responsible for the degradation of current space‐PV. By contrast, negligible reduction in PL of the individual perovskite subcells even after the highest dose studied is observed. Studying the intensity‐dependent PL of bare low‐gap and high‐gap perovskite absorbers, it is shown that the VOC, fill factor, and efficiency potentials remain identically high after irradiation. Radiation damage of all‐perovskite tandems thus has a fundamentally different origin to traditional space PV

Proton Radiation Hardness of Perovskite Tandem Photovoltaics.

Monolithic [Cs0.05(MA0. 17FA0. 83)0.95]Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon.F.L. acknowledges financial support from the Alexander von Humboldt Foundation via the Feodor Lynen program and thanks Prof. Sir R. Friend for supporting his Fellowship at the Cavendish Laboratory. This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement number 756962). M.J, A.A.A., E.K., and S.A. acknowledge financial support from the German Federal Ministry of Education and Research (BMBF) via program “Materialforschung für die Energiewende” (grant no. 03SF0540), by the German Federal Ministry for Economic Affairs and Energy (BMWi) through the ‘PersiST’ project (Grant No. 0324037C). T.B. C.A.K. and R.S. acknowledge funding by BMWi through the speedCIGS (grant no. 0324095E) and EFFCIS project (grant no. 0324076D). D.K. and M.C. acknowledge financial support from the Dutch Ministry of Economic Affairs, via The Top-consortia Knowledge and Innovation (TKI) Program ‘‘Photovoltaic modules based on a p-i-n stack, manufactured on a roll-to-roll line featuring high efficiency, stability and strong market perspective’’ (PVPRESS) (TEUE118010) and “Bridging the voltage gap” (BRIGHT) (1721101). K. F. acknowledges the George and Lilian Schiff Fund, the Engineering and Physical Sciences Research Council (EPSRC), the Winton Sustainability Fellowship, and the Cambridge Trust for funding. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). The authors acknowledge the EPSRC for funding (EP/R023980/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 841265. A.R.B. acknowledges funding from a Winton Studentship, Oppenheimer Studentship, and funding from the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Centre in Photovoltaics (CDT-PV). K.G. acknowledges the Polish Ministry of Science and Higher Education within the Mobilnosc Plus program (Grant No. 1603/MOB/V/2017/0)

21.6%-efficient monolithic perovskite/Cu(In,Ga)Se2 tandem solar cells with thin conformal hole transport layers for integration on rough bottom cell surfaces

Perovskite-based tandem solar cells can increase the power conversion efficiency (PCE) of conventional single-junction photovoltaic devices. Here, we present monolithic perovskite/CIGSe tandem solar cells with a perovskite top cell fabricated directly on an as-grown, rough CIGSe bottom cell. To prevent potential shunting due to the rough CIGSe surface, a thin NiOx layer is conformally deposited via atomic layer deposition on the front contact of the CIGSe bottom cell. The performance is further improved by an additional layer of the polymer PTAA at the NiOx/perovskite interface. This hole transport bilayer enables a 21.6% stabilized PCE of the tandem device at ∼0.8 cm2 active area. We use TEM/EDX measurements to investigate the deposition uniformity and conformality of the NiOx and PTAA layers. By absolute photoluminescence measurements, the contribution of the individual subcells to the tandem VOC is determined, revealing that further fine-tuning of the recombination layers might improve the tandem VOC. Finally, on the basis of the obtained results, we give guidelines to improve monolithic perovskite/CIGSe tandems toward predicted PCE estimates above 30%.BMBF, 03SF0540, Nachwuchsgruppe MeSa-Zuma: Entwicklung von spektral optimierten, hocheffizienten und langzeitstabilen Perowskit/Silizium Tandem SolarzellenBMWi, 0324095D, Verbundvorhaben: speedCIGS - Rechnerunterstützte Optimierung des CIGS-Depositionsprozesses in der industriellen Umsetzung; Teilvorhaben: Alkalibehandlung der CIGS Absorberoberfläche und monolithisch integrierte Tandem Zelle (p-TCM)BMWi, 0324076D, Verbundvorhaben: EFFCIS - Effizienzoptimierung von CIS-basierten Dünnschichtsolarzellen und -modulen; Teilvorhaben: Elektronenstrukturrechnungen zum Einfluss von Puffermaterialien auf die Eigenschaften des Cu(ln,Ga)(S,Se)2 Absorber

Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.BMBF, 03SF0540, Nachwuchsgruppe MeSa-Zuma: Entwicklung von spektral optimierten, hocheffizienten und langzeitstabilen Perowskit/Silizium Tandem SolarzellenBMWi, 0324288C, Verbundvorhaben: ProTandem - Demonstration der Produktionstauglichkeit von Perowskit-Silizium Tandemsolarzellen; Teilvorhaben: Entwicklung von Kontaktschichten für die Silizium-Heterojunction BottomzelleEC/H2020/763977/EU/Perovskite Thin-film Photovoltaics (PERTPV)/PERTPVDFG, 423749265, Identifizierung und Unterdrückung von Grenzflächenrekombination für hocheffiziente Perowskit-SolarzellenDFG, 402726906, SPP 2196: Perowskit-Halbleiter: Von fundamentalen Eigenschaften zur Anwendun

An open-access database and analysis tool for perovskite solar cells based on the FAIR data principles

Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences

Eliminierung von Grenzflächen-Verlusten in Perowskit-Einzelsolarzellen für effiziente Tandem-Solarzellen

Perovskite-based tandem solar cells have the potential to surpass single junction efficiency limits at low costs and to further spur the expansion of solar energy. This thesis deals with the optimization of tandem-relevant perovskite solar cells (PSCs), by mitigation of interfacial power losses between perovskite and charge-selective layers. A key theme in this work is the establishment of hole-selective self-assembled monolayers (SAMs), which can functionalize oxide surfaces in a self-limiting process with precise control. This enabled a simple and robust PSC structure with power conversion efficiencies of over 21% with single junction cells, over 24% with perovskite/CIGSe tandem solar cells and over 29% with perovskite/silicon tandem solar cells. It furthermore enabled studies on device-relevant model systems to gain understanding about optimal charge-selective layer design, characterization of charge extraction and stability enhancement. The gains in efficiency were rationalized by photoluminescence studies, both with absolute calibration for quantifying the voltage gains at the interfaces and with time resolution to investigate the charge carrier dynamics. By employing a combination of photoluminescence, solar cell characteristics and measurements of the energetic alignment between hole-selective layer and perovskite, we identified the energetic offset between the hole-accepting energy level of the SAM and the perovskite valence band maximum as the critical parameter that determined the open-circuit voltage (oc) of the solar cell. One of the studied SAMs, a carbazole unit attached to ethylphosphonic acid (2PACz), has shown optimal energetic alignment and minimal non-radiative recombination losses, rendering a “lossless” interface and enabling a oc of 1.19 V at 1.63 eV bandgap, without interlayers, dopants or additives. By using the SAM on rough CIGSe as hole-selective layer for the perovskite top cell, we have shown a certified 23.3%-efficient, monolithic perovskite/CIGSe tandem solar cell with 1 cm2 active area, which surpassed the previous record in size and efficiency (22.4% on 0.04 cm2), demonstrating how SAMs can simplify cell fabrication. Further optimization with a focus on the fill factor, the only parameter where best perovskite solar cells still lack behind mature solar cell technologies, led to the finding that a methyl-substituted carbazole-based SAM (Me-4PACz) considerably enhanced the hole-extraction speed and thus the fill factor (up to 84%), while keeping the high oc feature of 2PACz. By combining transient photoluminescence with photoconductivity measurements and solar cell data, we identified that the hole-selective interface was limiting the fill factor in p-i-n PSCs. Integrating Me-4PACz into perovskite/silicon tandem solar cells led to a certified record efficiency of 29.15% and to a cell retaining 95.5% of its initial efficiency after 300 h under continuous operation in ambient air. The results helped progressing perovskite tandem photovoltaics and might lay guides for future endeavors of industrial entry.Perowskit-basierte Tandemsolarzellen bergen das Potenzial, Einzelsolarzell-Effizienzen zu übertreffen und die Nutzung von Solarenergie auszuweiten. Die vorliegende Arbeit befasst sich mit der Optimierung von Tandem-relevanten Perowskitsolarzellen (PSZn) durch Reduktion von Leistungsverlusten an den Grenzflächen zwischen Perowskitschicht und den ladungsselektiven Schichten. Ein Hauptmotiv dieser Arbeit ist die Etablierung von Loch-selektiven selbstorganisierten Monolagen (SAMs), die Oxidschichten selbstständig funktionalisieren können. Dies ermöglichte eine einfache und robuste PSZ-Struktur mit Leistungsumwandlungseffizienzen (PCEs) von über 21% mit Einzelsolarzellen, >24% mit Perowskit/CIGSe Tandemsolarzellen und >29% mit Perowskit/Silizium Tandemsolarzellen. Außerdem ermöglichte es Solarzell-relevante Modellsysteme für einen Verständnisgewinn über optimales Design von ladungsselektiven Schichten, Ladungsträgerextraktion und Erhöhung der Stabilität. Die Effizienzgewinne wurden mit Photolumineszenz-Studien erklärt, sowohl mit absoluter Kalibrierung zur Quantifizierung von Spannungsgewinnen an den Grenzflächen, als auch mit Zeitauflösung, um die Ladungsträgerdynamik genauer zu untersuchen. Mit einer Kombination von Photolumineszenz, Solarzell-Eigenschaften und der Messung von Energieniveaus wurde die Ausrichtung zwischen Loch-selektiver Schicht und der Perowskit-Valenzbandkante als entscheidender Parameter für die Leerlaufspannung (Voc) der Solarzelle identifiziert. Einer der untersuchten SAMs, eine Carbazol-Einheit verbunden mit Ethanphosphonsäure (2PACz), zeigte optimale energetische Ausrichtung und minimale nichtstrahlende Verluste, was eine "verlustfreie" Grenzfläche ermöglichte und zu hohen Voc-Werten von bis zu 1,19 V bei 1,63 eV-Bandlücke führte, ohne Zwischenschichten, Dotierung oder Additiven. Durch einen SAM auf rauer CIGSe-Oberfläche als Loch-selektive Schicht für die Perowskit-Topzelle, wurde eine monolithische Perowskit/CIGSe Tandemzelle realisiert mit zertifizierter Effizienz von 23,3% auf einer Fläche von 1 cm2, was den vorigen Rekord in Fläche und Effizienz übertraf (22,4% auf 0,04 cm2). Weitere Optimierung mit Fokus auf den Füllfaktor der Solarzellen, den einzigen Parameter bei dem beste PSZn noch nicht die Werte von ausgereiften Solarzell-Technologien erreicht haben, führte zu der Erkenntnis, dass eine Methyl-substituierte Carbazol-SAM (Me-4PACz) die Loch-Extraktion deutlich beschleunigte und damit den Füllfaktor erhöhte (bis auf 84\%), unter Beibehaltung der hohen Voc von 2PACz. Durch transiente Photolumineszenz, Photo-Leitfähigkeitsmessungen und Solarzell-Daten ergab sich, dass die Loch-selektive Grenzfläche in p-i-n PSZn den Füllfaktor limitierte. Der Einsatz von Me-4PACz in Perowskit/Silizium-Tandemsolarzellen führte zu einer zertifizierten Rekordeffizienz von 29,15% und zu einer Zelle, die 95,5% ihrer Initialeffizienz nach 300\,h unter dauerhaftem Betrieb an Luft behielt