Publications by Henry Snaith

Direct Observation of Ultrafast Exciton Dissociation in Lead Iodide Perovskite by 2D Electronic Spectroscopy

ACS PHOTONICS 5 (2018) 852-860

A Jha, H-G Duan, V Tiwari, PK Nayak, HJ Snaith, M Thorwart, RJD Miller

Surface modified fullerene electron transport layers for stable and reproducible flexible perovskite solar cells

NANO ENERGY 49 (2018) 324-332

S Song, R Hill, K Choi, K Wojciechowski, S Barlow, J Leisen, HJ Snaith, SR Marder, T Park

Aligned and Graded Type-II Ruddlesden–Popper Perovskite Films for Efficient Solar Cells

Advanced Energy Materials 8 (2018)

J Qing, XK Liu, M Li, F Liu, Z Yuan, E Tiukalova, Z Yan, M Duchamp, S Chen, Y Wang, S Bai, JM Liu, HJ Snaith, CS Lee, TC Sum, F Gao

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Recently, Ruddlesden–Popper perovskites (RPPs) have attracted increasing interests due to their promising stability. However, the efficiency of solar cells based on RPPs is much lower than that based on 3D perovskites, mainly attributed to their poor charge transport. Herein, a simple yet universal method for controlling the quality of RPP films by a synergistic effect of two additives in the precursor solution is presented. RPP films achieved by this method show (a) high quality with uniform morphology, enhanced crystallinity, and reduced density of sub-bandgap states, (b) vertically oriented perovskite frameworks that facilitate efficient charge transport, and (c) type-II band alignment that favors self-driven charge separation. Consequently, a hysteresis-free RPP solar cell with a power conversion efficiency exceeding 12%, which is much higher than that of the control device (1.5%), is achieved. The findings will spur new developments in the fabrication of high-quality, aligned, and graded RPP films essential for realizing efficient and stable perovskite solar cells.

The effect of ionic composition on acoustic phonon speeds in hybrid perovskites from Brillouin spectroscopy and density functional theory


IV Kabakova, I Azuri, Z Chen, PK Nayak, HJ Snaith, L Kronik, C Paterson, AA Bakulin, DA Egger

Present status and future prospects of perovskite photovoltaics.

Nature materials 17 (2018) 372-376

HJ Snaith

In situ simultaneous photovoltaic and structural evolution of perovskite solar cells during film formation


M Alsari, O Bikondoa, J Bishop, M Abdi-Jalebi, LY Ozer, M Hampton, P Thompson, MT Horantner, S Mahesh, C Greenland, JE Macdonald, G Palmisano, HJ Snaith, DG Lidzey, SD Stranks, RH Frienda, S Lilliu

Evidence of Nitrogen Contribution to the Electronic Structure of the CH3 NH3 PbI3 Perovskite.

Chemistry (Weinheim an der Bergstrasse, Germany) 24 (2018) 3539-3544

M Kot, K Wojciechowski, H Snaith, D Schmeißer

Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the organic methylammonium cation (CH3 NH3+ ) in the methylammonium lead triiodide (CH3 NH3 PbI3 ) perovskite film. From one side it is reported that the organic cation does not contribute to electronic structure of the CH3 NH3 PbI3 film. From the other side, valence band maximum fluctuations, dependent on the CH3 NH3+ rotation, have been theoretically predicted. The resonant X-ray photoelectron spectroscopy results reported here show experimental evidence of nitrogen contribution to the CH3 NH3 PbI3 electronic structure. Moreover, the observed strong resonances of nitrogen with the I 5s and the Pb 5d-6s levels indicate that the CH3 NH3 PbI3 valence band is extended up to ≈18 eV below the Fermi energy, and therefore one should also consider these shallow core levels while modeling its electronic structure.

Perovskite/Colloidal Quantum Dot Tandem Solar Cells: Theoretical Modeling and Monolithic Structure

ACS ENERGY LETTERS 3 (2018) 869-874

A Karani, L Yang, S Bai, MH Futscher, HJ Snaith, B Ehrler, NC Greenham, D Di

Nonspiro, Fluorene-Based, Amorphous Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells.

Advanced science (Weinheim, Baden-Wurttemberg, Germany) 5 (2018) 1700811-

Š Daškevičiū Tė, N Sakai, M Franckevičius, M Daškevičienė, A Magomedov, V Jankauskas, HJ Snaith, V Getautis

Novel nonspiro, fluorene-based, small-molecule hole transporting materials (HTMs) V1050 and V1061 are designed and synthesized using a facile three-step synthetic route. The synthesized compounds exhibit amorphous nature with a high glass transition temperature, a good solubility, and decent thermal stability. The planar perovskite solar cells (PSCs) employing V1050 generated an excellent power conversion efficiency of 18.3%, which is comparable to 18.9% obtained with the state-of-the-art Spiro-OMeTAD. Importantly, the devices based on V1050 and V1061 show better stability compared to devices based on Spiro-OMeTAD when aged without any encapsulation under uncontrolled humidity conditions (relative humidity around 60%) in the dark and under continuous full sun illumination.

Enabling reliability assessments of pre-commercial perovskite photovoltaics with lessons learned from industrial standards

NATURE ENERGY 3 (2018) 459-465

HJ Snaith, P Hacke

Correction to "Exciton-Dominated Core-Level Absorption Spectra of Hybrid Organic-Inorganic Lead Halide Perovskites".

The journal of physical chemistry letters 9 (2018) 3193-

C Vorwerk, C Hartmann, C Cocchi, G Sadoughi, SN Habisreutinger, R Félix, RG Wilks, HJ Snaith, M Bär, C Draxl

Enhanced photovoltage for inverted planar heterojunction perovskite solar cells.

Science (New York, N.Y.) 360 (2018) 1442-1446

D Luo, W Yang, Z Wang, A Sadhanala, Q Hu, R Su, R Shivanna, GF Trindade, JF Watts, Z Xu, T Liu, K Chen, F Ye, P Wu, L Zhao, J Wu, Y Tu, Y Zhang, X Yang, W Zhang, RH Friend, Q Gong, HJ Snaith, R Zhu

The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Exciton-Dominated Core-Level Absorption Spectra of Hybrid Organic-Inorganic Lead Halide Perovskites.

The journal of physical chemistry letters 9 (2018) 1852-1858

C Vorwerk, C Hartmann, C Cocchi, G Sadoughi, SN Habisreutinger, R Félix, RG Wilks, HJ Snaith, M Bär, C Draxl

In a combined theoretical and experimental work, we investigate X-ray absorption near-edge structure spectroscopy of the I L3 and the Pb M5 edges of the methylammonium lead iodide (MAPbI3) hybrid inorganic-organic perovskite and its binary phase PbI2. The absorption onsets are dominated by bound excitons with sizable binding energies of a few hundred millielectronvolts and pronounced anisotropy. The spectra of both materials exhibit remarkable similarities, suggesting that the fingerprints of core excitations in MAPbI3 are essentially given by its inorganic component, with negligible influence from the organic groups. The theoretical analysis complementing experimental observations provides the conceptual insights required for a full characterization of this complex material.

Consolidation of the optoelectronic properties of CH3NH3PbBr3 perovskite single crystals.

Nature communications 8 (2017) 590-

B Wenger, PK Nayak, X Wen, SV Kesava, NK Noel, HJ Snaith

Ultralow trap densities, exceptional optical and electronic properties have been reported for lead halide perovskites single crystals; however, ambiguities in basic properties, such as the band gap, and the electronic defect densities in the bulk and at the surface prevail. Here, we synthesize single crystals of methylammonium lead bromide (CH3NH3PbBr3), characterise the optical absorption and photoluminescence and show that the optical properties of single crystals are almost identical to those of polycrystalline thin films. We observe significantly longer lifetimes and show that carrier diffusion plays a substantial role in the photoluminescence decay. Contrary to many reports, we determine that the trap density in CH3NH3PbBr3 perovskite single crystals is 1015 cm-3, only one order of magnitude lower than in the thin films. Our enhanced understanding of optical properties and recombination processes elucidates ambiguities in earlier reports, and highlights the discrepancies in the estimation of trap densities from electronic and optical methods.Metal halide perovskites for optoelectronic devices have been extensively studied in two forms: single-crystals or polycrystalline thin films. Using spectroscopic approaches, Wenger et al. show that polycrystalline thin films possess similar optoelectronic properties to single crystals.

Investigating the Role of 4-Tert Butylpyridine in Perovskite Solar Cells


SN Habisreutinger, NK Noel, HJ Snaith, RJ Nicholas

Trends in Perovskite Solar Cells and Optoelectronics: Status of Research and Applications from the PSCO Conference

ACS ENERGY LETTERS 2 (2017) 857-861

F De Angelis, D Meggiolaro, E Mosconi, A Petrozza, MK Nazeeruddin, HJ Snaith

Electron injection and scaffold effects in perovskite solar cells.

Journal of materials chemistry. C, Materials for optical and electronic devices 5 (2017) 634-644

M Anaya, W Zhang, BC Hames, Y Li, F Fabregat-Santiago, ME Calvo, HJ Snaith, H Míguez, I Mora-Seró

In spite of the impressive efficiencies reported for perovskite solar cells (PSCs), key aspects of their working principles, such as electron injection at the contacts or the suitability of the utilization of a specific scaffold layer, are not yet fully understood. Increasingly complex scaffolds attained by the sequential deposition of TiO2 and SiO2 mesoporous layers onto transparent conducting substrates are used to perform a systematic characterization of both the injection process at the electron selective contact and the scaffold effect in PSCs. By forcing multiple electron injection processes at a controlled sequence of perovskite-TiO2 interfaces before extraction, interfacial injection effects are magnified and hence characterized in detail. An anomalous injection behavior is observed, the fingerprint of which is the presence of significant inductive loops in the impedance spectra with a magnitude that correlates with the number of interfaces in the scaffold. Analysis of the resistive and capacitive behavior of the impedance spectra indicates that the scaffolds could hinder ion migration, with positive consequences such as lowering the recombination rate and implications for the current-potential curve hysteresis. Our results suggest that an appropriate balance between these advantageous effects and the unavoidable charge transport resistive losses introduced by the scaffolds will help in the optimization of PSC performance.

Hydrophobic Organic Hole Transporters for Improved Moisture Resistance in Metal Halide Perovskite Solar Cells.

ACS applied materials & interfaces 8 (2016) 5981-5989

T Leijtens, T Giovenzana, SN Habisreutinger, JS Tinkham, NK Noel, BA Kamino, G Sadoughi, A Sellinger, HJ Snaith

Solar cells based on organic-inorganic perovskite semiconductor materials have recently made rapid improvements in performance, with the best cells performing at over 20% efficiency. With such rapid progress, questions such as cost and solar cell stability are becoming increasingly important to address if this new technology is to reach commercial deployment. The moisture sensitivity of commonly used organic-inorganic metal halide perovskites has especially raised concerns. Here, we demonstrate that the hygroscopic lithium salt commonly used as a dopant for the hole transport material in perovskite solar cells makes the top layer of the devices hydrophilic and causes the solar cells to rapidly degrade in the presence of moisture. By using novel, low cost, and hydrophobic hole transporters in conjunction with a doping method incorporating a preoxidized salt of the respective hole transporters, we are able to prepare efficient perovskite solar cells with greatly enhanced water resistance.

Research Update: Strategies for improving the stability of perovskite solar cells

APL MATERIALS 4 (2016) ARTN 091503

SN Habisreutinger, DP McMeekin, HJ Snaith, RJ Nicholas

Pinhole-free perovskite films for efficient solar modules


W Qiu, T Merckx, M Jaysankar, CM de la Huerta, L Rakocevic, W Zhang, UW Paetzold, R Gehlhaar, L Froyen, J Poortmans, D Cheyns, HJ Snaith, P Heremans