Imperial College London

DrSaifHaque

Faculty of Natural SciencesDepartment of Chemistry

Reader in Materials Chemistry
 
 
 
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Contact

 

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

 
 
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Location

 

164bChemistrySouth Kensington Campus

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Summary

 

Publications

Publication Type
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126 results found

Aristidou N, Eames C, Sanchez-Molina I, Bu X, Kosco J, Islam MS, Haque SA, Aristidou N, Eames C, Sanchez-Molina I, Bu X, Kosco J, Islam MS, Haque SA, Aristidou N, Eames C, Sanchez-Molina I, Bu X, Kosco J, Islam MS, Haque SA, Aristidou N, Eames C, Sanchez-Molina I, Bu X, Kosco J, Islam MS, Haque SA, 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, Pages: 15218-15218, 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. Perovskite films based on CH3NH3PbI3 undergo rapid degradation when exposed to oxygen and light. Here, we report mechanistic insights into this oxygen-induced photodegradation from a range of experimental and computational techniques. We find fast oxygen diffusion into CH3NH3PbI3 films is accompanied by photo-induced formation of highly reactive superoxide species. Perovskite films composed of small crystallites show higher yields of superoxide and lower stability. Ab initio simulations indicate that iodide vacancies are the preferred sites in mediating the photo-induced formation of superoxide species from oxygen. Thin-film passivation with iodide salts is shown to enhance film and device stability. The understanding of degradation phenomena gained from this study is important for the future design and optimization of stable perovskite solar cells.

JOURNAL ARTICLE

Bruno A, Borriello C, Di Luccio T, Sessa L, Concilio S, Haque SA, Minarini C, 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

Mokhtar MZ, Chen M, Whittaker E, Hamilton B, Aristidou N, Ramadan S, Gholinia A, Haque SA, O'Brien P, Saunders BR, Mokhtar MZ, Chen M, Whittaker E, Hamilton B, Aristidou N, Ramadan S, Gholinia A, Haque SA, O'Brien P, Saunders BR, Mokhtar MZ, Chen M, Whittaker E, Hamilton B, Aristidou N, Ramadan S, Gholinia A, Haque SA, O'Brien P, Saunders BR, Mokhtar MZ, Chen M, Whittaker E, Hamilton B, Aristidou N, Ramadan S, Gholinia A, Haque SA, O'Brien P, Saunders BR, 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

Perovskite solar cells continue to attract strong attention because of their unprecedented rate of power conversion efficiency increase. CH3NH3PbI3 (MAPbI3) is the most widely studied perovskite. Typically one-step (1-s) or two-step (2-s) deposition methods are used to prepare MAPbI3 films. Here, we investigate a new MAPbI3 film formation method that combines 1-s and 2-s deposition (termed 1 & 2-s) and uses systematic variation of the stoichiometric mole ratio (x) for the PbI2 + xMAI solutions employed. The PbI2 + xMAI solutions were used to deposit precursor films that were subsequently dipped in MAI solution as a second step to produce the final MAPbI3 films. The morphologies of the 1 & 2-s MAPbI3 films consisted of three crystal types: tree-like microcrystals (≫1 μm), cuboid meso-crystals (∼0.1-1 μm) and nanocrystals (∼50-80 nm). Each crystal type and their proportions were controlled by the value for x. The new 1 & 2-s deposition method produced MAPbI3 films with tuneable optoelectronic properties that were related to those for the conventional 1-s and 2-s films. However, the 1 & 2-s film properties were not simply a combination of those for the 1-s and 2-s films. The 1 & 2-s films showed enhanced light scattering and the photoluminescence spectra displayed a morphologically-dependent red-shift. The unique morphologies for the 1 & 2-s films also strongly influenced PbI2 conversion, power conversion efficiency, hysteresis and recombination. The trends for the performance parameters and hysteresis were compared for devices constructed using spiro-MeOTAD and P3HT and were similar. The 1 & 2-s method should apply to other perovskite formulations and the new insights concerning MAPbI3 crystal growth conditions, morphology and material properties established in this study should also be transferable.

JOURNAL ARTICLE

Pont S, Bryant D, Lin C-T, Aristidou N, Wheeler S, Ma X, Godin R, Haque SA, Durrant JR, Pont S, Bryant D, Lin CT, Aristidou N, Wheeler S, Ma X, Godin R, Haque SA, Durrant JR, Pont S, Bryant D, Lin C-T, Aristidou N, Wheeler S, Ma X, Godin R, Haque SA, Durrant JR, Pont S, Bryant D, Lin CH, Aristidou N, Wheeler S, Ma X, Godin R, Haque S, Durrant JRet al., 2017, Tuning CH3NH3Pb(I1-xBrx)(3) perovskite oxygen stability in thin films and solar cells, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 5, Pages: 9553-9560, ISSN: 2050-7488

© The Royal Society of Chemistry 2017. 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 CH 3 NH 3 Pb(I 1-x Br x ) 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, CH 3 NH 3 PbBr 3 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 CH 3 NH 3 Pb(I 1-x Br x ) 3 perovskites, but that CH 3 NH 3 PbBr 3 provides an opportunity to develop inherently stable high voltage photovoltaic devices and 4-Terminal tandem solar cells.

JOURNAL ARTICLE

Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchuangchutchaval T, Wheeler S, Durrant JR, Haque SA, Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchuangchutchaval T, Wheeler S, Durrant JR, Haque SA, Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchuangchutchaval T, Wheeler S, Durrant JR, Haque SA, Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchuangchutchaval 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 (vol 9, pg 1655, 2016), ENERGY & ENVIRONMENTAL SCIENCE, Vol: 9, Pages: 1850-1850, ISSN: 1754-5692

JOURNAL ARTICLE

Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchunangatchaval T, Wheeler S, Durrant JR, Haque SA, Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchunangatchaval T, Wheeler S, Durrant JR, Haque SA, Bryant D, Aristidou N, Pont S, Sanchez-Molina I, Chotchunangatchaval T, Wheeler S, Durrant JR, Haque SA, 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 & ENVIRONMENTAL SCIENCE, Vol: 9, Pages: 1655-1660, ISSN: 1754-5692

© 2016 The Royal Society of Chemistry. Here, we demonstrate that light and oxygen-induced degradation is the main reason for the low operational stability of methylammonium lead triiodide (MeNH 3 PbI 3 ) perovskite solar cells exposed to ambient conditions. When exposed to both light and dry air, unencapsulated MeNH 3 PbI 3 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 O 2 . In contrast, significantly slower degradation is observed when the MeNH 3 PbI 3 devices are exposed to moisture alone (e.g. 85% relative humidity in N 2 ). 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 O 2 - . These observations demonstrate that the operational stability of electronic and optoelectronic devices that exploit the electron transporting properties of MeNH 3 PbI 3 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 PRF, Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PRF, Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PRF, Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PR, Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PRF, 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

Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SA, Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SA, Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SA, Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SA, Aristidou N, Sanchez-Molina I, Chotchuangchutchaval T, Brown M, Martinez L, Rath T, Haque SA, 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: 1433-7851

In this paper we report on the influence of light and oxygen on the stability of CH3 NH3 PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2 O3 /CH3 NH3 PbI3 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-Al2 O3 film is replaced with an mp-TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3 NH3 PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.

JOURNAL ARTICLE

Bruno A, Commodo M, Haque SA, Minutolo P, 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

Cao Y, Bernechea M, Maclachlan A, Zardetto V, Creatore M, Haque SA, Konstantatos G, 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

Hu Y, Sanchez-Molina I, Haque SA, Robertson N, 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, Vol: 2015, Pages: 5864-5873, ISSN: 1434-1948

JOURNAL ARTICLE

Li X, Hu Y, Sanchez-Molina I, Zhou Y, Yu F, Haque SA, Wu W, Hua J, Tian H, Robertson N, 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

MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall A-C, Buchmaier C, Trimmel G, Nelson J, Haque SA, MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall A-C, Buchmaier C, Trimmel G, Nelson J, Haque SA, MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall AC, Buchmaier C, Trimmel G, Nelson J, Haque SA, MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall AC, Buchmaier C, Trimmel G, Nelson J, Haque SA, 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

In this work, molecular tuning of metal xanthate precursors is shown to have a marked effect on the heterojunction morphology of hybrid poly(3-hexylthiophene-2,5-diyl) (P3HT)/CdS blends and, as a result, the photochemical processes and overall performance of in situ fabricated hybrid solar cells. A series of cadmium xanthate complexes is synthesized for use as in situ precursors to cadmium sulfide nanoparticles in hybrid P3HT/CdS solar cells. The formation of CdS domains is studied by simultaneous GIWAXS (grazing incidence wide-angle X-ray scattering) and GISAXS (grazing incidence small-angle X-ray scattering), revealing knowledge about crystal growth and the formation of different morphologies observed using TEM (transmission electron microscopy). These measurements show that there is a strong relationship between precursor structure and heterojunction nanomorphology. A combination of TAS (transient absorption spectroscopy) and photovoltaic device performance measurements is used to show the intricate balance required between charge photogeneration and percolated domains in order to effectively extract charges to maximize device power conversion efficiencies. This study presents a strong case for xanthate complexes as a useful route to designing optimal heterojunction morphologies for use in the emerging field of hybrid organic/inorganic solar cells, due to the fact that the nanomorphology can be tuned via careful design of these precursor materials.

JOURNAL ARTICLE

O'Mahony FTF, Lee YH, Jellett C, Dmitrov S, Bryant DTJ, Durrant JR, O'Regan BC, Graetzel M, Nazeeruddin MK, Haque SA, O'Mahony FTF, Lee YH, Jellett C, Dmitrov S, Bryant DTJ, Durrant JR, O'Regan BC, Graetzel M, Nazeeruddin MK, Haque SA, 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: 2050-7488

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

Rath T, Gury L, Sanchez-Molina I, Martinez L, Haque SA, Rath T, Gury L, Sánchez-Molina I, Martínez L, Haque SA, Rath T, Gury L, Sánchez-Molina I, Martínez L, Haque SA, Rath T, Gury L, Sánchez-Molina I, Martínez L, Haque SA, Rath T, Gury L, Sánchez-Molina I, Martínez L, Haque SA, 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: 1359-7345

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

Rath T, MacLachlan AJ, Brown MD, Hague SA, Rath T, MacLachlan AJ, Brown MD, Haque SA, Rath T, MacLachlan AJ, Brown MD, Haque SA, Rath T, MacLachlan AJ, Brown MD, Haque SA, 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: 2050-7488

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, Borriello C, Haque SA, Minarini C, Di Luccio T, Bruno A, Borriello C, Haque SA, Minarini C, Di Luccio T, Bruno A, Borriello C, Haque SA, Minarini C, Di Luccio T, 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

Hybrid heterojunctions of conjugated polymers and inorganic nanomaterials are a promising combination for obtaining high performance solar cells (SC). In this work we have explored new possible uses of the WS2 nanotubes (NTs) both as the only acceptor material blended with a polymer and in ternary systems mixed with a polymer and quantum dots (QDs). In particular we have spectroscopically investigated binary blends of poly(3-hexylthiophene) (P3HT) and WS2 NTs, P3HT and CdSe QDs, and ternary blends of P3HT, CdSe QDs and WS2 NTs. We report fluorescence quenching effects of the QD signal in the P3HT-CdSe-WS2 system with the increase of NT concentration. Static and time-resolved fluorescence studies reveal efficient resonant energy transfer from the QDs to the NTs upon photoexcitation. The evidence of energetic interaction between WS2 NTs and QDs opens new fields of application of WS2 NTs and holds very promising potential for improving charge transfer phenomena in the active layer of hybrid solar cells.

JOURNAL ARTICLE

Bruno A, Di Luccio T, Borriello C, Villani F, Haque SA, Minarini C, Bruno A, Di Luccio T, Borriello C, Villani F, Haque S, Minarini Cet al., 2014, Exciton Dynamics in Hybrid Polymer/QD Blends, E-MRS Spring Meeting / Symposium D on Advanced Inorganic Materials and Structures for Photovoltaics, Publisher: ELSEVIER SCIENCE BV, Pages: 167-175, ISSN: 1876-6102

CONFERENCE PAPER

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 J, Guilbert AAY, Schmidt M, Bruno A, Yao J, King S, Tuladhar SM, Kirchartz T, Alonso MI, Goñi 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

Lindblad R, Cappel UB, O'Mahony FTF, Siegbahn H, Johansson EMJ, Haque SA, Rensmo H, Lindblad R, Cappel UB, O'Mahony FTF, Siegbahn H, Johansson EMJ, Haque SA, Rensmo H, Lindblad R, Cappel UB, O'Mahony FT, Siegbahn H, Johansson EM, Haque SA, Rensmo H, 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

Semiconductor sensitized solar cell interfaces have been studied with photoelectron spectroscopy to understand the interfacial electronic structures. In particular, the experimental energy level alignment has been determined for complete TiO2/metal sulfide/polymer interfaces. For the metal sulfides CdS, Sb2S3 and Bi2S3 deposited from single source metal xanthate precursors, it was shown that both driving forces for electron injection into TiO2 and hole transfer to the polymer decrease for narrower bandgaps. The energy level alignment results were used in the discussion of the function of solar cells with the same metal sulfides as light absorbers. For example Sb2S3 showed the most favourable energy level alignment with 0.3 eV driving force for electron injection and 0.4 eV driving force for hole transfer and also the most efficient solar cells due to high photocurrent generation. The energy level alignment of the TiO2/Bi2S3 interface on the other hand showed no driving force for electron injection to TiO2, and the performance of the corresponding solar cell was very low.

JOURNAL ARTICLE

MacLachlan AJ, O'Mahony FTF, Sudlow AL, Hill MS, Molloy KC, Nelson J, Haque SA, MacLachlan AJ, O'Mahony FTF, Sudlow AL, Hill MS, Molloy KC, Nelson J, Haque SA, MacLachlan AJ, O'Mahony FT, Sudlow AL, Hill MS, Molloy KC, Nelson J, Haque SA, MacLachlan AJ, O'Mahony FTF, Sudlow AL, Hill MS, Molloy KC, Nelson J, Haque SAet al., 2014, Solution- Processed Mesoscopic Bi2S3: Polymer Photoactive Layers, CHEMPHYSCHEM, Vol: 15, Pages: 1019-1023, ISSN: 1439-4235

The fabrication of solution-processed nontoxic mesoporous Bi2S3 structures is demonstrated and the suitability of these structures for use in hybrid solar cells investigated. Mesoporous Bi2S3 electrodes are prepared via thermal decomposition of a thin film composed of a bismuth xanthate single source precursor. The resultant Bi2S3 films are made up of regular needles with approximate dimensions of 50×500 nm, as confirmed by scanning electron microscopy (SEM). The crystallinity of the Bi2S3 is found to be dependent on the annealing temperature, as determined by X-ray diffraction. The porous Bi2S3 films are infiltrated with the hole conductor P3HT to generate novel hybrid films, and laser-based transient absorption spectroscopy is used to interrogate the charge-separation reaction at the resulting Bi2S3/P3HT heterojunction. Specifically, optical excitation of the hybrid films results in efficient and long-lived charge separation (microsecond to millisecond timescale), thereby rendering such films suitable for the development of novel low-cost solar-energy conversion devices.

JOURNAL ARTICLE

Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos G, Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos G, Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos G, Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos G, Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos Get al., 2014, Improved electronic coupling in hybrid organic-inorganic nanocomposites employing thiol-functionalized P3HT and bismuth sulfide nanocrystals, NANOSCALE, Vol: 6, Pages: 10018-10026, ISSN: 2040-3364

In this study, we employ a thiol-functionalized polymer (P3HT-SH) as a leverage to tailor the nanomorphology and electronic coupling in polymer-nanocrystal composites for hybrid solar cells. The presence of the thiol functional group allows for a highly crystalline semiconducting polymer film at low thiol content and allows for improved nanomorphologies in hybrid organic-inorganic systems when employing non-toxic bismuth sulfide nanocrystals. The exciton dissociation efficiency and carrier dynamics at this hybrid heterojunction are investigated through photoluminescence quenching and transient absorption spectroscopy measurements, revealing a larger degree of polaron formation when P3HT-SH is employed, suggesting an increased electronic interaction between the metal chalcogenide nanocrystals and the thiol-functionalized P3HT. The fabricated photovoltaic devices show 15% higher power conversion efficiencies as a result of the improved nanomorphology and better charge transfer mechanism together with the higher open circuit voltages arising from the deeper energy levels of P3HT-SH.

JOURNAL ARTICLE

Pearson AJ, Watters DC, Yi H, Sarjadi MS, Reynolds LX, Marchisio PP, Kingsley J, Haque SA, Iraqi A, Lidzey DG, Pearson AJ, Watters DC, Yi H, Sarjadi MS, Reynolds LX, Marchisio PP, Kingsley J, Haque SA, Iraqi A, Lidzey DG, 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

Piper RB, Yoshida M, Farrell DJ, Khoury T, Crossley MJ, Schmidt TW, Haque SA, Ekins-Daukes NJ, Piper RB, Yoshida M, Farrell DJ, Khoury T, Crossley MJ, Schmidt TW, Haque SA, Ekins-Daukes NJet al., 2014, Kinetic insight into bimolecular upconversion: experiment and simulation, RSC ADVANCES, Vol: 4, Pages: 8059-8063, ISSN: 2046-2069

JOURNAL ARTICLE

Wood S, Garnett O, Tokmoldin N, Tsoi WC, Haque SA, Kim J-S, Wood S, Garnett O, Tokmoldin N, Tsoi WC, Haque SA, Kim J-S, Wood S, Garnett O, Tokmoldin N, Tsoi WC, Haque SA, Kim JS, Wood S, Garnett O, Tokmoldin N, Tsoi WC, Haque SA, Kim J-Set al., 2014, In situ formation of organic-inorganic hybrid nanostructures for photovoltaic applications, FARADAY DISCUSSIONS, Vol: 174, Pages: 267-279, ISSN: 1359-6640

The performance of hybrid (organic-inorganic) photovoltaic devices is critically dependent on the thin film morphology. This work studies the film formation process using the in situ thermal decomposition of a soluble precursor to form a well-distributed network of CdS nanoparticles within a poly(3-hexylthiophene) (P3HT) polymer matrix. Resonant Raman spectroscopy is used to probe the formation of the inorganic nanoparticles and the corresponding changes in the molecular order of the polymer. We find that the CdS precursor decomposes rapidly upon heating to 160 °C, but that this has a disruptive effect on the P3HT. The extent of this disruption can be controlled by adjusting the annealing temperature, and nanowire aggregates of P3HT are found to have increased susceptibility. Atomic force microscopy reveals that at high temperatures (>200 °C), cracks form in the film, resulting in a 'plateau'-like microstructure. In order to retain the preferable 'granular' microstructure and to control the molecular disruption, low decomposition temperatures are needed. This work identifies a particular problem for optimising the hybrid thin film morphology and shows how it can be partially overcome.

JOURNAL ARTICLE

Arar M, Gruber M, Edler M, Haas W, Hofer F, Bansal N, Reynolds LX, Haque SA, Zojer K, Trimmel G, Rath T, Arar M, Gruber M, Edler M, Haas W, Hofer F, Bansal N, Reynolds LX, Haque SA, Zojer K, Trimmel G, Rath T, Arar M, Gruber M, Edler M, Haas W, Hofer F, Bansal N, Reynolds LX, Haque SA, Zojer K, Trimmel G, Rath T, Arar M, Gruber M, Edler M, Haas W, Hofer F, Bansal N, Reynolds LX, Haque SA, Zojer K, Trimmel G, Rath T, Arar M, Gruber M, Edler M, Haas W, Hofer F, Bansal N, Reynolds LX, Haque SA, Zojer K, Trimmel G, Rath Tet al., 2013, Influence of morphology and polymer: nanoparticle ratio on device performance of hybrid solar cells-an approach in experiment and simulation, NANOTECHNOLOGY, Vol: 24, Pages: 484005-484005, ISSN: 0957-4484

We present a thorough study on the various impacts of polymer:nanoparticle ratios on morphology, charge generation and device performance in hybrid solar cells, comprising active layers consisting of a conjugated polymer and in situ prepared copper indium sulfide (CIS) nanoparticles. We conducted morphological studies through transmission electron microscopy and transient absorption measurements to study charge generation in absorber layers with polymer:nanoparticle weight ratios ranging from 1:3 to 1:15. These data are correlated to the characteristic parameters of the prepared solar cells. To gain a deeper understanding of our experimental findings, three-dimensional drift-diffusion-based simulations were performed. Based on elaborate descriptions of the contributions of polymer and nanoparticle phase to device performances, our results suggest that a polymer:CIS volume ratio of 1:2 (weight ratio 1:9) is necessary to obtain a balanced hole and electron percolation. Also at higher CIS loadings the photocurrent remains surprisingly high due to the contribution of the CIS phase to the charge carrier generation.

JOURNAL ARTICLE

Bansal N, O'Mahony FTF, Lutz T, Haque SA, Bansal N, O'Mahony FTF, Lutz T, Haque SA, Bansal N, O'Mahony FTF, Lutz T, Haque SAet al., 2013, Solution Processed Polymer-Inorganic Semiconductor Solar Cells Employing Sb2S3 as a Light Harvesting and Electron Transporting Material, ADVANCED ENERGY MATERIALS, Vol: 3, Pages: 986-990, ISSN: 1614-6832

JOURNAL ARTICLE

Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS, Zhang W, Nielsen CB, McCulloch I, Rebois DG, Kirchartz T, Hill MS, Molloy KC, Nelson J, Haque SA, Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS, Zhang W, Nielsen CB, McCulloch I, Rebois DG, Kirchartz T, Hill MS, Molloy KC, Nelson J, Haque SA, Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS, Zhang W, Nielsen CB, McCulloch I, Rebois DG, Kirchartz T, Hill MS, Molloy KC, Nelson J, Haque SA, Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS, Zhang W, Nielsen CB, McCulloch I, Rebois DG, Kirchartz T, Hill MS, Molloy KC, Nelson J, Haque SA, Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS, Zhang W, Nielsen CB, McCulloch I, Rebois DG, Kirchartz T, Hill MS, Molloy KC, Nelson J, Haque SAet al., 2013, Influence of Crystallinity and Energetics on Charge Separation in Polymer-Inorganic Nanocomposite Films for Solar Cells, SCIENTIFIC REPORTS, Vol: 3, ISSN: 2045-2322

The dissociation of photogenerated excitons and the subsequent spatial separation of the charges are of crucial importance to the design of efficient donor-acceptor heterojunction solar cells. While huge progress has been made in understanding charge generation at all-organic junctions, the process in hybrid organic:inorganic systems has barely been addressed. Here, we explore the influence of energetic driving force and local crystallinity on the efficiency of charge pair generation at hybrid organic:inorganic semiconductor heterojunctions. We use x-ray diffraction, photoluminescence quenching, transient absorption spectroscopy, photovoltaic device and electroluminescence measurements to demonstrate that the dissociation of photogenerated polaron pairs at hybrid heterojunctions is assisted by the presence of crystalline electron acceptor domains. We propose that such domains encourage delocalization of the geminate pair state. The present findings suggest that the requirement for a large driving energy for charge separation is relaxed when a more crystalline electron acceptor is used.

JOURNAL ARTICLE

Bruno A, Borriello C, Di Luccio T, Nenna G, Sessa L, Concilio S, Haque SA, Minarini C, Bruno A, Borriello C, Di Luccio T, Nenna G, Sessa L, Concilio S, Haque SA, Minarini Cet al., 2013, White light-emitting nanocomposites based on an oxadiazole-carbazole copolymer (POC) and InP/ZnS quantum dots, JOURNAL OF NANOPARTICLE RESEARCH, Vol: 15, ISSN: 1388-0764

JOURNAL ARTICLE

Bruno A, Del Mauro ADG, Nenna G, Haque SA, Minarini C, Bruno A, Mauro ADGD, Nenna G, Haque SA, Minarini Cet al., 2013, Insights on photophysical proprieties of DCM dye in PVK host matrix, POLYMER COMPOSITES, Vol: 34, Pages: 1500-1505, ISSN: 0272-8397

JOURNAL ARTICLE

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