Imperial College London

ProfessorSaifHaque

Faculty of Natural SciencesDepartment of Chemistry

Professor of Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 1886s.a.haque

 
 
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Location

 

110HMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

137 results found

Aziz A, Aristidou N, Bu X, Westbrook RJE, Hague SA, Islam MSet al., 2020, Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites, CHEMISTRY OF MATERIALS, Vol: 32, Pages: 400-409, ISSN: 0897-4756

Journal article

Lanzetta L, Aristidou N, Haque SA, 2020, Stability of lead and tin halide perovskites: the link between defects and degradation, The Journal of Physical Chemistry Letters, Vol: 11, Pages: 574-585, ISSN: 1948-7185

The field of photovoltaic research has been lately dominated by the rapid evolution of low-cost and high-efficiency hybrid organic lead halide perovskite solar cells. Despite the considerable progress made in the efficiency of such devices, the achievement of long-term material and device stability remains a challenge. In this Perspective, insights into the role structural defects play in the stability of these perovskite absorbers are examined, highlighting the critical importance of vacancy type defects as the initiation sites for moisture-, oxygen-, and light-induced degradation and the approaches that are emerging to help overcome these issues. In the second part of the Perspective we consider the stability of tin-based perovskites. Here, the Sn4+ defects that arise upon material degradation are described along with the strategies being developed to enhance stability and decrease their formation. Finally, the discussion is extended to innately more stable layered tin-based perovskites, identifying them as a route to the development of efficient lead-free perovskite solar cells.

Journal article

Yoo B, Ding D, Marin-Beloqui JM, Lanzetta L, Bu X, Rath T, Haque SAet al., 2019, Improved Charge Separation and Photovoltaic Performance of BiI3 Absorber Layers by Use of an In Situ Formed BiSI Interlayer, ACS APPLIED ENERGY MATERIALS, Vol: 2, Pages: 7056-7061, ISSN: 2574-0962

Journal article

Speller EM, Clarke AJ, Aristidou N, Wyatt MF, Francàs L, Fish G, Cha H, Lee HKH, Luke J, Wadsworth A, Evans AD, McCulloch I, Kim JS, Haque SA, Durrant JR, Dimitrov SD, Tsoi WC, Li Zet al., 2019, Toward improved environmental stability of polymer:fullerene and polymer:non-fullerene organic solar cells: a common energetic origin of light and oxygen induced degradation, ACS Energy Letters, Vol: 4, Pages: 846-852, ISSN: 2380-8195

With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation.

Journal article

Lin C-T, Rossi F, Kim J, Baker J, Ngiam J, Xu S, Pont S, Aristidou N, Haque S, Watson T, McLachlan M, Durrant Jet al., 2019, Evidence for surface defect passivation as the origin of the remarkable photostability of unencapsulated perovskite solar cells employing aminovaleric acid as a processing additive, Journal of Materials Chemistry A, Vol: 7, ISSN: 2050-7496

This study addresses the cause of enhanced stability of methyl ammonium lead iodide when processed with aminovaleric acid additives (AVA-MAPbI3) in screen printed, hole transport layer free perovskite solar cells with carbon top electrodes (c-PSC). Employing AVA as an additive in the active layer caused a 40-fold increase in device lifetime measured under full sun illumination in ambient air (RH ~15%). This stability improvement with AVA was also observed in optical photobleaching studies of planar films on glass, indicating this improvement is intrinsic to the perovskite film. Employing low-energy ion scattering spectroscopy, photoluminescence studies as a function of AVA and oxygen exposure, and a molecular probe for superoxide generation, we conclude that even though superoxide is generated in both AVA-MAPbI3 and MAPbI3 films, AVA located at grain boundaries is able to passivate surface defect sites, resulting in enhanced resistivity to oxygen induced degradation. These results are discussed in terms of their implications for the design of environmentally stable perovskite solar cells.

Journal article

Ding D, Rath T, Lanzetta L, Marin-Beloqui J, Haque SAet al., 2018, Efficient hybrid solar cells based on solution processed mesoporous TiO2 / Tin (II) sulfide heterojunctions, ACS Applied Energy Materials, Vol: 1, Pages: 3042-3047, ISSN: 2574-0962

Tin monosulfide (SnS) is emerging as a promising absorber material for the development of low-cost, solution-processable solar cells. Herein, we present a straightforward, solution-based route for the preparation of tin monosulfide (SnS) films employing a green solvent, namely, tetrahydrofuran (THF). We show that the surface coverage and the morphology of the SnS films can be tuned by modification of the precursor solution composition and film deposition conditions. Furthermore, we explore the effect of a PEDOT:PSS interlayer and fabricate solar cells based on the following architecture: FTO/planar-TiO2/mesoporous-TiO2/SnS/P3HT/PEDOT:PSS/Ag. Devices based on this architecture are shown to exhibit power conversion efficiencies (PCEs) of 3.0%, thus demonstrating the potential of our method for the development of low-cost and environmentally friendly solar cells.

Journal article

Westbrook RJE, Haque S, Sanchez-Molina I, Marin-Beloqui JM, Bronstein Het al., 2018, The Effect of Interfacial Energetics on Charge Transfer from Lead Halide Perovskite to Organic Hole Conductors, Journal of Physical Chemistry C, Vol: 122, Pages: 1326-1332, ISSN: 1932-7447

The control and optimization of interfacial charge transfer processes is crucial to the design of efficient perovskite solar cells. Herein, we measure the yield and kinetics of hole transfer across the methylammonium lead triiodide perovskite|polymeric hole transport material heterojunction, as a function of the interfacial energy offset, ∆E between the highest occupied molecular orbital of the hole transport material and the valence band of the perovskite. A combination of steady-state and time-resolved photoluminescence, along with transient absorption spectroscopy revealed that only a small driving energy (∆E~0.07eV) is required to induce highly efficient hole transfer. The findings of this paper suggest that further improvements in the open-circuit voltage, and so the power conversion efficiency, of perovskite solar cells could be achieved by incorporating hole transport materials that provide an interfacial energy offset in the range 0 < ∆E < 0.18eV.

Journal article

Aristidou, Eames C, Islam MS, Haque SAet al., 2017, Insights into the increased degradation rate of CH3NH3PbI3 solar cells in combined water and O2 environments, Journal of Materials Chemistry A, Vol: 5, Pages: 25469-25475, ISSN: 2050-7496

Halide perovskites offer low cost and high efficiency solar cell materials but serious issues related to air and moisture stability remain. In this study we show, using UV-vis, fluorescence and time of flight secondary ion mass spectrometry (ToF-SIMS) techniques, that the degradation of methylammonium lead iodide solar cells is significantly accelerated when both air and moisture are present in comparison to when just air or moisture is present alone. Using ab initio computational techniques we identify the thermodynamic driving force for the enhanced reactivity and highlight the regions of the photoexcited material that are the most likely reaction centres. We suggest that water catalyses the reaction by stabilising the reactive superoxide species, enabling them to react with the methylammonium cation.

Journal article

Chen M, Mokhtar MZ, Whittaker E, Lian Q, Hamilton B, O'Brien P, Zhu M, Cui Z, Haque SA, Saunders BRet al., 2017, Reducing hole transporter use and increasing perovskite solar cell stability with dual-role polystyrene microgel particles, NANOSCALE, Vol: 9, Pages: 10126-10137, ISSN: 2040-3364

Journal article

Lanzetta Lopez L, Marin-Beloqui JM, Sanchez-Molina I, Ding D, Haque SAet al., 2017, Two-dimensional organic tin Halide Perovskites with tunable visible emission and their use in light-emitting devices, ACS Energy Letters, Vol: 2, Pages: 1662-1668, ISSN: 2380-8195

Hybrid organic lead trihalide perovskites continue to generate significant interest for use in optoelectronic devices such as solar cells and light-emitting devices. However, the toxicity of lead is considered one of the main obstacles to the commercialization of this technology. Although challenging, the replacement of lead by tin is currently the most promising alternative. Herein, we explore a class of low-dimensional, lead-free perovskite materials (2D (PEA)2SnIxBr4–x, where PEA ≡ C6H5CH2CH2NH3+) with tunable optical properties in the visible region of the spectrum. Specifically, we show that 2D (PEA)2SnI4 perovskite exhibits superior photoluminescence properties to conventional 3D CH3NH3SnI3 and that (PEA)2SnI4 can act as a sensitizer on mesoporous TiO2. We go on to demonstrate visible (∼630 nm) electroluminescence from a device employing a (PEA)2SnI4 emitter sandwiched between ITO/PEDOT:PSS and F8/LiF/Al as hole and electron injection electrodes, respectively. These devices reach a luminance of 0.15 cd/m2 at 4.7 mA/cm2 and an efficacy of 0.029 cd/A at 3.6 V. This proof-of-principle device indicates a viable path to low-dimensional, lead-free perovskite optoelectronics.

Journal article

Aristidou N, Haque S, Eames C, Sanchez-Molina I, Bu X, Kosco J, Saiful Islam M, Haque SAet al., 2017, Fast oxygen diffusion and iodide defects mediate oxygen-induced degradation of perovskite solar cells, Nature Communications, Vol: 8, ISSN: 2041-1723

Methylammonium lead halide perovskites are attracting intense interest as promising materials for next-generation solar cells, but serious issues related to long-term stability need to be addressed. Specifically, perovskite films based on CH3NH3PbI3 undergo fast oxygen- and light-induced degradation. However, the mechanism of such degradation and its relation to particle size and oxygen transport are poorly understood. Here, we report new mechanistic insights through the combined use of isothermal gravimetric analysis, photoluminescence, secondary ion mass spectrometry and ab initio simulation techniques. We find fast oxygen diffusion into CH3NH3PbI3 films is accompanied by superoxide formation, which are critical to degradation by oxygen in the atmosphere.Perovskite films composed of small crystallites show high yields of photo-induced superoxide species and low stability. Ab initio simulations indicate that iodide vacancies are the preferred sites in mediating the photo-induced formation of superoxide species from oxygen. We also show that thin-film passivation with iodide salts can lead to enhanced film stability and thus device stability. The understanding of degradation phenomena gained from this study is important for the future design and optimisation of perovskite solar cells with greater stability.

Journal article

Bruno A, Borriello C, Di Luccio T, Sessa L, Concilio S, Haque SA, Minarini Cet al., 2017, Oxadiazole-carbazole polymer (POC)-Ir(ppy)(3) tunable emitting composites, OPTICAL MATERIALS, Vol: 66, Pages: 166-170, ISSN: 0925-3467

Journal article

Pont S, Bryant D, Lin CH, Aristidou N, Wheeler S, Ma X, Godin R, Haque S, Durrant JRet al., 2017, Tuning CH 3 NH 3 Pb(I 1-x Br x ) 3 Perovskite Oxygen Stability in Thin Films and Solar Cells, Journal of Materials Chemistry A, Vol: 5, ISSN: 2050-7488

The rapid development of organic–inorganic lead halide perovskites has resulted in high efficiency photovoltaic devices. However the susceptibility of these devices to degradation under environmental stress has so far hindered commercial development, requiring for example expensive device encapsulation. Herein, we have investigated the stability of CH3NH3Pb(I1−xBrx)3 [x = 0–1] thin films and solar cells under controlled humidity, light, and oxygen conditions. We show that higher bromide ratios increase tolerance to moisture, with x = 1 thin films being stable to 120 h of moisture stress. Under light and dry air, partial bromide (x < 1) substitution does not enhance film stability significantly, with the corresponding solar cells degrading within two hours. In contrast, CH3NH3PbBr3 films show excellent stability, with device stability being limited by the organic interlayer. For these x = 1 films, we show that charge carriers are quenched in the presence of oxygen and form superoxide; however in contrast to perovskites containing iodide, this superoxide does not degrade the crystal. Our observations show that iodide limits the oxygen and light stability of CH3NH3Pb(I1−xBrx)3 perovskites, but that CH3NH3PbBr3 provides an opportunity to develop inherently stable high voltage photovoltaic devices and 4-terminal tandem solar cells.

Journal article

Mokhtar MZ, Chen M, Whittaker E, Hamilton B, Aristidou N, Ramadan S, Gholinia A, Haque SA, O'Brien P, Saunders BRet al., 2017, CH3NH3PbI3 films prepared by combining 1-and 2-step deposition: how crystal growth conditions affect properties, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 19, Pages: 7204-7214, ISSN: 1463-9076

Journal article

Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchuangchutchaval T, Wheeler S, Durrant JR, Haque SAet al., 2016, Correction: Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells, Energy & Environmental Science, Vol: 9, Pages: 1850-1850, ISSN: 1754-5706

Journal article

Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchunangatchaval T, Wheeler S, Durrant JR, Haque SAet al., 2016, Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells, Energy and Environmental Science, Vol: 9, Pages: 1655-1660, ISSN: 1754-5692

Here, we demonstrate that light and oxygen-induced degradation is the main reason for the low operational stability of methylammonium lead triiodide (MeNH3PbI3) perovskite solar cells exposed to ambient conditions. When exposed to both light and dry air, unencapsulated MeNH3PbI3 solar cells rapidly degrade on timescales of minutes to a few hours. This rapid degradation is also observed under electrically bias driven current flow in the dark in the presence of O2. In contrast, significantly slower degradation is observed when the MeNH3PbI3 devices are exposed to moisture alone (e.g. 85% relative humidity in N2). We show that this light and oxygen induced degradation can be slowed down by the use of interlayers that are able to remove electrons from the perovskite film before they can react with oxygen to form O2-. These observations demonstrate that the operational stability of electronic and optoelectronic devices that exploit the electron transporting properties of MeNH3PbI3 will be critically dependent upon the use of suitable barrier layers and device configurations to mitigate the oxygen sensitivity of this remarkable material.

Journal article

Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PRFet al., 2016, Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces, Scientific Reports, Vol: 6, ISSN: 2045-2322

Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.

Journal article

Hu Y, Sanchez-Molina I, Haque SA, Robertson Net al., 2015, Ruthenium Dyes with Azo Ligands: Light Harvesting, Excited-State Properties and Relevance to Dye-Sensitised Solar Cells, EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Pages: 5864-5873, ISSN: 1434-1948

Journal article

Rath T, MacLachlan AJ, Brown MD, Hague SAet al., 2015, Structural, optical and charge generation properties of chalcostibite and tetrahedrite copper antimony sulfide thin films prepared from metal xanthates, Journal of Materials Chemistry A, Vol: 3, Pages: 24155-24162, ISSN: 2050-7496

Herein, we report on a solution based approach for the preparation of thin films of copper antimony sulfide, an emerging absorber material for third generation solar cells. In this work, copper and antimony xanthates are used as precursor materials for the formation of two different copper antimony sulfide phases: chalcostibite (CuSbS2) and tetrahedrite (Cu12Sb4S13). Both phases were thoroughly investigated regarding their structural and optical properties. Moreover, thin films of chalcostibite and tetrahedrite were prepared on mesoporous TiO2 layers and photoinduced charge transfer in these metal sulfide/TiO2 heterojunctions was studied via transient absorption spectroscopy. Photoinduced charge transfer was detected in both the chalcostibite as well as the tetrahedrite sample, which is an essential property in view of applying these materials as light-harvesting agents in semiconductor sensitized solar cells.

Journal article

Bruno A, Commodo M, Haque SA, Minutolo Pet al., 2015, Spectroscopic investigation of flame synthesized carbon nanoparticle/P3HT blends, CARBON, Vol: 94, Pages: 955-961, ISSN: 0008-6223

Journal article

Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SAet al., 2015, The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers, Angewandte Chemie-International Edition, Vol: 54, Pages: 8208-8212, ISSN: 1521-3773

In this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2O3/CH3NH3PbI3 photoactive layers rapidly decompose yielding methylamine, PbI2, and I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2− species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2− generation is significantly reduced when the mp-Al2O3 film is replaced with an mp-TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.

Journal article

Rath T, Gury L, Sanchez-Molina I, Martinez L, Haque SAet al., 2015, Formation of porous SnS nanoplate networks from solution and their application in hybrid solar cells, Chemical Communications, Vol: 51, Pages: 10198-10201, ISSN: 1364-548X

Herein, we present a facile solution-based route towards nanostructured, hybrid absorber layers based on tin mono-sulfide (SnS), an emerging, non-toxic absorber material for low-cost and large-scale PV applications. Charge photogeneration properties in the hybrid system are studied using transient absorption spectroscopy and fabricated solar cells show efficient photocurrent generation over a broad spectral range.

Journal article

Cao Y, Bernechea M, Maclachlan A, Zardetto V, Creatore M, Haque SA, Konstantatos Get al., 2015, Solution Processed Bismuth Sulfide Nanowire Array Core/Silver Sulfide Shell Solar Cells, CHEMISTRY OF MATERIALS, Vol: 27, Pages: 3700-3706, ISSN: 0897-4756

Journal article

O'Mahony FTF, Lee YH, Jellett C, Dmitrov S, Bryant DTJ, Durrant JR, O'Regan BC, Graetzel M, Nazeeruddin MK, Haque SAet al., 2015, Improved environmental stability of organic lead trihalide perovskite-based photoactive-layers in the presence of mesoporous TiO2, Journal of Materials Chemistry A, Vol: 3, Pages: 7219-7223, ISSN: 2050-7496

Impressive hybrid photovoltaic device performances have been realised with the methylammonium lead triiodide (MAPbI3) perovskite absorber in a wide range of device architectures. However, the question as to which of these systems represents the most commercially viable long-term prospect is yet to be answered conclusively. Here, we report on the photoinduced charge transfer processes in MAPbI3 based films measured under inert and ambient conditions. When exposed to ambient conditions, the coated mesoporous Al2O3 and bilayer systems show a rapid and significant degradation in the yield of long-lived charge separation. This process, which does not affect sensitized-mesoporous TiO2 films, is only found to occur when both light and oxygen are present. These observations indicate that the presence of a mesostructured TiO2 electron acceptor to rapidly extract the photoexcited electron from the perovskite sensitizer may be crucial for fundamental photovoltaic stability and significantly increases innate tolerance to environmental conditions. This work highlights a significant advantage of retaining mesoscale morphological control in the design of perovskite photovoltaics.

Journal article

MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall A-C, Buchmaier C, Trimmel G, Nelson J, Haque SAet al., 2015, Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance, ADVANCED FUNCTIONAL MATERIALS, Vol: 25, Pages: 409-420, ISSN: 1616-301X

Journal article

Li X, Hu Y, Sanchez-Molina I, Zhou Y, Yu F, Haque SA, Wu W, Hua J, Tian H, Robertson Net al., 2015, Insight into quinoxaline containing D-pi-A dyes for dye-sensitized solar cells with cobalt and iodine based electrolytes: the effect of pi-bridge on the HOMO energy level and photovoltaic performance, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 3, Pages: 21733-21743, ISSN: 2050-7488

Journal article

Guilbert AAY, Schmidt M, Bruno A, Yao J, King S, Tuladhar SM, Kirchartz T, Alonso MI, Goni AR, Stingelin N, Haque SA, Campoy-Quiles M, Nelson Jet al., 2014, Spectroscopic Evaluation of Mixing and Crystallinity of Fullerenes in Bulk Heterojunctions, ADVANCED FUNCTIONAL MATERIALS, Vol: 24, Pages: 6972-6980, ISSN: 1616-301X

Journal article

Bruno A, Borriello C, Haque SA, Minarini C, Di Luccio Tet al., 2014, Ternary hybrid systems of P3HT-CdSe-WS2 nanotubes for photovoltaic applications, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 17998-18003, ISSN: 1463-9076

Journal article

Pearson AJ, Watters DC, Yi H, Sarjadi MS, Reynolds LX, Marchisio PP, Kingsley J, Haque SA, Iraqi A, Lidzey DGet al., 2014, Impact of dithienyl or thienothiophene units on the optoelectronic and photovoltaic properties of benzo[1,2,5]thiadiazole based donor–acceptor copolymers for organic solar cell devices, RSC Advances, Vol: 4, Pages: 43142-43149, ISSN: 2046-2069

We report a comparative study on four donor–acceptor benzothiadiazole-based copolymers containing dithienyl or thienothiophene moieties for application in organic photovoltaic (OPV) devices. Bulk-heterojunction OPV devices are fabricated having power conversion efficiencies ranging between 4 and 6%. Morphological, spectroscopic and charge-transport measurements are used to investigate the influence of either the dithienyl or thienothiophene moieties on the structure and photophysical properties of the copolymer and copolymer:PC71BM blend films and rationalise the solar cell characteristics. Although all copolymer:PC71BM blends exhibit comparable hole polaron yields, solar cell devices with the highest power conversion efficiencies are correlated with increased charge-carrier mobility of the copolymer and enhanced aggregation of PC71BM in the blend.

Journal article

Lindblad R, Cappel UB, O'Mahony FTF, Siegbahn H, Johansson EMJ, Haque SA, Rensmo Het al., 2014, Energy level alignment in TiO2/metal sulfide/polymer interfaces for solar cell applications, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 17099-17107, ISSN: 1463-9076

Journal article

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