Using solar energy and water to convert biomass-derived 5-hydroxymethylfurfural (HMF) into valuable chemicals, while simultaneously producing green hydrogen, offers a promising recycling approach for a significant source of agricultural waste. Here, we report the design of a selective, stable and efficient HMF photocatalyst by the structural engineering of graphitic carbon nitride nanosheets. Our optimal few-layered nanosheet structure loaded with Pt clusters demonstrates high photocatalytic performance, achieving selective photooxidation of HMF to valuable 2,5-diformylfuran and 5-formyl-2-furancarboxylic acid, and the co-production of hydrogen at a high evolution rate of 75.52 +/- 0.46 & micro;mol gcat-1 h-1, over 10 days of photoreforming. Density functional theory and comprehensive physicochemical characterisation reveal a synergistic effect of the Pt and carbon nitride surfaces, with the former enhancing water adsorption and dissociation and the latter providing a high density of COOH, -CO, and -COH adsorption sites for HMF. These insights into the optimal structuring of carbon nitride nanosheets provide a promising direction for the design of efficient photocatalysts for photoreforming with impact on various sustainable chemical recycling approaches.

Photon upconversion has potential applications in light-emitting diodes, photocatalysis, bio-imaging, microscopy, 3D printing, and photovoltaics. Bulk lead-halide perovskites have emerged as promising sensitisers for solid-state photon upconversion via triplet-triplet annihilation due to their excellent optoelectronic properties. In this system, a perovskite-sensitiser absorbs photons and subsequently generates triplet excitons in an adjacent emitter material, where triplet-triplet annihilation can occur, allowing for the emission of higher energy photons. However, a major loss pathway in perovskite-sensitised upconversion is the back-transfer of singlet excitons from the emitter to the sensitiser via F & ouml;rster Resonance Energy Transfer. In this investigation, a 2D perovskite spacer layer is introduced between the bulk perovskite-sensitiser and rubrene emitter to mitigate back-transfer of singlet excitons. This modification reveals the inherent balance between efficient triplet exciton transfer across the interface with a potential barrier vs the mitigation of near-field back-transfer by increasing the distance between the sensitiser and singlet excitons in the emitter. Notably, the introduction of this spacer layer enhances the relative upconversion efficiency at lower excitation power densities while also sustaining performance over extended timescales. This work represents significant progress toward the practical applications of perovskite-sensitised photon upconversion.

The successful development of optoelectronic devices is contingent on a detailed understanding of interactions between light and excited energy states in photoactive materials. In 2D perovskites, excitons are the dominant photogenerated species and their energetic structure plays a pivotal role, governing photon absorption and emission processes. In these materials, dark exciton states can undergo photoluminescence due to relaxation of selection rules and this process can be modulated by an external magnetic field, enabling unambiguous identification of the exciton fine structure. Previous reports of magneto-optical spectroscopy on 2D perovskites are restricted to the macroscopic response, where key information is lost regarding the microscopic heterogeneity of the photoluminescence. Here, magneto-optical microscopy is used for the first time on perovskite materials to elucidate the spatial variation of exciton emission processes. In 2D perovskite thin films, regions of localized bright and dark exciton populations are distinguished, correlated to the film morphology. In single crystals, dark excitons become localised at the edges, where excitons can be trapped in two distinct types of sub-gap states. This work represents significant progress in understanding the properties of exciton emission in 2D perovskites, which is crucial for the development and optimization of optoelectronic technology.

Wide bandgap (WBG) metal halide perovskite solar cells with high output voltages are critical for high efficiency multi‐junction solar cells. This work demonstrates the first use of laser annealing in ambient for fabricating both the self‐assembly molecular (SAM) hole transport layer (HTL) and the perovskite layer for 1.80 eV perovskite solar cells with impressive open circuit voltage ( V OC ) and power conversion efficiency (PCE). The V OC of 1.35V and PCE of 19.8% produced by the champion cell are the highest‐to‐date for perovskite solar cells with the same bandgap. Notably, laser annealing reduces processing time to only 1 min each for the HTL and the perovskite layer compared to 10 min each for the HTL and the perovskite layer by hot‐plate thermal annealing for the same device area. Additionally, laser annealing subjects the substrate to lower temperature than hot‐plate annealing. Macroscopic and localized temperature profiles generated by laser annealing were modeled by a 3D finite element analysis for the first time unveiling effective laser power absorption and cooling by the perovskite film compared to Me‐4PACz and unveiling heat transport to the rest of the substrate during laser scanning. This work demonstrates promising prospects of laser annealing for future mass production of perovskite solar cells especially on temperature‐sensitive substrates.

Nanomaterials with a strong room-temperature optical response to magnetic fields are highly desirable for applications in sensing and photonics. Therefore, the ability to tune this response presents an opportunity to develop nanoscale magneto-optical devices. 2D metal halide perovskites are promising materials for optoelectronics, but typically exhibit very weak magneto-optical effects at room temperature. In this article, a 15× enhancement of the magnetic field effect on photoluminescence (magneto-photoluminescence) is demonstrated in colloidal (PEA)2PbI4 2D perovskite nanosheets at room temperature. The results show that an external species can influence the exchange interaction energy and consequently the splitting between bright and dark exciton states in 2D perovskite nanosheets, which ultimately governs the magneto-photoluminescence. Additionally, the average photoluminescence quantum yield (PLQY) is increased from 15.2% in bulk single crystals to 23.1% in nanosheets (with a maximum recorded PLQY of 39.61%) produced using liquid-phase exfoliation, which also exhibited reduced trap emission compared with bulk or tape-exfoliated crystals in this study. This work demonstrates a simple method of engineering exciton states in 2D perovskites, assisting the development of optoelectronic technology and representing a crucial step toward producing nanoscale room-temperature magneto-optical devices.

Determining the Role of 2D Perovskite Passivation Layer on Bulk Perovskite-Sensitised Photochemical UpconversionNicholas Sloane a, b, Jianghui Zheng c, d, Christopher G. Bailey a, b, Anita W. Y. Ho-Baillie c, d, e, Timothy W. Schmidt b, f, Dane R. McCamey a, ba School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australiab ARC Centre of Excellence in Exciton Sciencec School of Physics, University of Sydney, Sydney, NSW, Australiad The University of Sydney Nano Institute, Sydney, Australiae University of New South Wales, Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Engineering, Sydney 2052, Sydney, Australiaf School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, AustraliaInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Nicholas Sloane, presentation 044DOI: https://doi.org/10.29363/nanoge.hopv.2024.044Publication date: 6th February 2024Bulk perovskite films have proved to be excellent candidates for photovoltaic devices due to their remarkable optoelectrical properties. However, a major drawback is their relative instability due to rapid degradation and defect formation in ambient conditions. One method of countering these drawbacks is to utilise a thin, 2D perovskite passivating layer on top of a bulk perovskite film, effectively combining the high efficiencies seen in 3D films with the increased stability of 2D films [1]. Whilst such alterations have shown promising results for photovoltaic devices, the feasibility of utilising passivated perovskite films for other applications such as solar energy conversion have not yet been studied. Incorporating excitonic processes demonstrated by certain organic semiconductors could potentially bypass the detailed balance limit imposed on traditional single junction solar cells [2]. These processes include multiple exciton generation by high energy photons reducing thermalisation losses or by converting multiple low energy, below band-gap photons into one high energy photon. The latter process is commonly referred to as "photon upconversion" and can be achieved in certain organic semiconducting materials via sensitised triplet-triplet annihilation where two spin-1 triplet excitons combine to form one emissive spin-0 singlet exciton. Due to the high absorption cross-section of bulk perovskite films at near infrared wavelengths they have emerged as promising solid-state sensitisers to generate triplet excitons in an adjacent organic semiconductor film [3], where direct optical generation of triplet excitons is spin-forbidden. In this presentation we present the first observation of bulk perovskite sensitised upconversion using a 2D passivation layer. We investigate the role that the 2D perovskite intermediary layer plays in the upconversion process is in both the impact of the passivating layer on the bulk perovskite and for the upconverting performance of the system. This presentation explores the inherent balance between reduced transport across the interface due to the introduction of a potential barrier versus the reduction of parasitic back transfer by increasing the distance between the strongly absorbing sensitiser and annihilator. Such experimental results raise important questions on the nature of energy transfer across a bulk perovskite/2D perovskite/organic semiconductor interface. This observation holds implications not only for the emerging field of perovskite-sensitised upconversion but also for broader research endeavours exploring interfaces between hybrid and organic semiconductors. References:[1] Chen, P.; Bai, Y.; Wang, S.; Lyu, M.; Yun, J-H.; Wang, L. In Situ Growth of 2D Perovskite Capping Layer for Stable and Efficient Perovskite Solar Cells. Adv Funct Mater 28, 1706923 (2018).[2] Tayebjee, M. J. Y.; McCamey, D. R.; Schmidt, T. W. Beyond Shockley–Queisser: Molecular Approaches to High-Efficiency Photovoltaics. J Phys Chem Lett 6, 2367–2378 (2015).[3] Nienhaus, L.; Correa-Baena, J-P.; Wieghold, S.; Einzinger, M.; Lin, T-A.; Shulenberger, K.E.; Klein, N.D.; Wu, M.; Bulović, V.; Buonassisi, T.; Baldo, M.A.; Bawendi, M.G. Triplet-Sensitization by Lead Halide Perovskite Thin Films for Near-Infrared-to-Visible Upconversion. ACS Energy Lett 4, 888–895 (2019).Acknowledgements:D.R.M., T.W.S, N.S and C.G.B acknowledge the support of the Australian Research Council (ARC) Centre of Excellence in Exciton Science (CE170100026). N.S acknowledges the Australian Government Research Training Program (RTP) for a PhD scholarship. J. Z. acknowledges the support by the Australian Renewable Energy Agency (ARENA) via projects 2020 RND001 and 2020 RND003. A H.-B. is supported by the Australian Research Council (ARC) Future Fellowships FT210100210. © FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.MATSUSPreviously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.International Conference on Hybrid and Organic PhotovoltaicsInternational Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and OptoelectronicsThe main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and OptoelectronicsThe International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.

Here, we report gas-quenched quasi-2D (GA)(MA)(5)Pb5I16 perovskites for single junction solar cells and monolithic-silicon tandem solar cells. This is the first time quasi-2D (GA)(MA)(5)Pb5I16 perovskite cells have been tested with proton beams, showing excellent tolerance. A representative tandem cell also passed the IEC 61215 Thermal Cycling Test (-40 degrees C <-> 85 degrees C) twice, retaining 95.0% of its initial PCE after 400 cycles.

Perovskite films have rapidly emerged as leading active materials in optoelectronic devices due to their strong optical absorption, high carrier mobility and ease of fabrication. Whilst proving to be promising materials for solar cells and light-emitting diodes, another application of perovskites which makes effective use of their unique properties is sensitisation for photon upconversion. Consisting of a bulk perovskite sensitiser alongside an adjacent organic semiconductor film, the upconverting system can absorb multiple low-energy photons to emit high-energy photons. In this work, density functional theory, in conjunction with GW theory, is utilised to investigate the electronic structure at the MAPbI$_3$/rubrene interface for different surface terminations of MAPbI$_3$. From this investigation, we reveal that the surface termination of the perovskite layer greatly affects the charge density at the interface and within the rubrene layer driven by the formation of interfacial dipole layers. The formation of a strong interfacial dipole for the lead-iodide terminated perovskite alters the band alignment of the heterojunction and is expected to facilitate more efficient hole transfer. For the perovskite surface terminated with the methylammonium iodide layer, the highest occupied molecular orbital of the adjacent rubrene layer lies deep within the perovskite band gap. This termination type is further characterized by a lower density of states near the band edges thereby acting as a spacer which is anticipated to decrease the probability of charge transfer across the interface. Thus based on our results, PbI$_2$-terminated perovskite surfaces are predicted to be favourable for applications where hole transfer to a rubrene layer is ideal, highlighting the significance of surface termination for all systems where the electronic environment at the interface is crucial to performance.

Metal halide perovskite solar cells have achieved tremendous progress and have attracted enormous research and development efforts since the first report of demonstration in 2009. Due to fabrication versatility, many heat treatment methods can be utilized to achieve perovskite film crystallization. Herein, 10.6 mu m carbon dioxide laser process is successfully developed for the first time for perovskite film crystallization. In addition, this is the first time formamidinium lead triiodide solar cells by laser annealing under ambient are demonstrated. The champion cell produces a power conversion efficiency of 21.8%, the highest for laser-annealed perovskite cells. And this is achieved without any additive, passivation, or post-treatment.

Two-dimensional (2D) organic-inorganic metal halide perovskites have gained immense attention as alternatives to three-dimensional (3D) perovskites in recent years. The hydrophobic spacers in the layered structure of 2D perovskites make them more moisture-resistant than 3D perovskites. Moreover, they exhibit unique anisotropic electrical transport properties due to a structural confinement effect. In this study, four lead-free Dion-Jacobson (DJ) Sn-based phase perovskite single crystals, 3AMPSnI4, 4AMPSnI4, 3AMPYSnI4, and 4AMPYSnI4 [AMP = (aminomethyl)-piperidinium, AMPY = (aminomethyl)pyridinium] are reported. Results reveal structural differences between them impacting the resulting optical properties. Namely, higher octahedron distortion results in a higher absorption edge. Density functional theory (DFT) is also performed to determine the trends in energy band diagrams, exciton binding energies, and formation energies due to structural differences among the four single crystals. Finally, a field-effect transistor (FET) based on 4AMPSnI4 is demonstrated with a respectable hole mobility of 0.57 cm2 V-1 s-1 requiring a low threshold voltage of only -2.5 V at a drain voltage of -40 V. To the best of our knowledge, this is the third DJ-phase perovskite FET reported to date.

Perovskite whentandemed with organic photovoltaics (OPV) for double-junctions have efficiencypotentials over 40%. However, there is still room for improvement suchas better current matching, higher fill factor, as well as lower voltage and fill factor losses in the top perovskite cell. Here weaddress the issue associated with the top perovskite cell by utilising anovel halogenated polycyclic aromatic hydrocarbon compound, 1-naphthylammoniumchloride (NA & horbar;Cl) playing dual roles of surface modification for the hole selectivelayer (HSL) and passivation of HSL/perovskiteinterface. Results of X-ray photoelectron spectroscopy and density functionaltheory calculations reveal that NA & horbar;Cl retains self-assembly property for the HSLwhile demonstrating high dipole moment and polarizability. This induces asurface dipole at the HSL/perovskite interface reducing the energetic barrierfor hole extraction by 210 meV thereby enhancing voltage output and fill factorof the device. Such scheme when implemented in a high bandgap (1.78 eV)perovskite solar cell, results in a respectable efficiency of 19.7% and thehighest fill factor of 85.4% amongst those of 1.78 eV perovskite cells reported.We have also achieved 23% cell efficient monolithic perovskite-OPV tandem withan impressive fill factor of 84%, which is the highest for perovskite-OPVtandem cells reported to-date.

The organic spacer cation plays a crucial role in determining the exciton fine structure in 2D perovskites. Here, magneto‐optical spectroscopy is used to gain insight into the influence of the organic spacer on dark excitons in Ruddlesden–Popper (RP) perovskites. Using modest magnetic field strengths (<1.5 T), the optically forbidden dark exciton state can be identified and its emission properties significantly modulated via application of in‐plane magnetic fields, up to temperatures of 15 K. At low temperatures, an increase in collected photoluminescence efficiency of >30% is demonstrated, signifying the critical role of the dark exciton state for light‐emitting applications of 2D perovskites. The exciton fine structure and the degree of magnetic‐field‐induced mixing are significantly impacted by the choice of organic spacer cation, with 4–methoxyphenylethylammonium (MeO‐PEA) showing the largest effect due to larger bright–dark exciton splitting. This study distinguishes between interior (bulk) and surface dark‐exciton emission, showing that bright–dark exciton splitting differs between the interior and surface. The results emphasize the significance of the organic spacer cation in controlling the exciton fine structure in 2D perovskites and have important implications for the development of optoelectronic technology based on 2D perovskites.

C60 is a widely used electron selective material for p-i-n perovskite cells, however, its energy level does not match well with that of a wide-bandgap perovskite, resulting in low open-circuit voltage (VOC) and fill factor (FF). To overcome this issue, ultra-thin LiF has been widely used as an interlayer between C60 and perovskite layers facilitating efficient electron extraction but resulting in instability. In this work, the use of a piperidinium bromide (PpBr) is reported as an interlayer between C60 and perovskite, and the interlayer further is optimized by introducing an additional oxygen atom on the opposite side of the NH2+. This results in morpholinium bromide (MLBr) with increased dipole moment. Because of this, MLBr is highly effective in minimizing the energy band mismatch between perovskite and C60 layer for electron extraction while at the same time passivating defects. The champion single junction 1.67 eV MLBr solar cell produced a PCE of 21.9% and the champion monolithic MLBr perovskite-Si tandem cell produced a PCE of 28.8%. Most importantly, both encapsulated MLBr and PpBr devices retain over 97% of their initial efficiency after 400 thermal cycles (between -40 and 85 degrees C), twice the number of cycles specified by the International Electrotechnical Commission (IEC) 61215 photovoltaic module standard. A dipole interlayer such as morpholinium bromide (MLBr) between C60 and a 1.67 eV perovskite layer is effective in defect passivation and energy band alignment for charge extraction. Champion single junction and 1 cm2 perovskite-Si tandem devices produced PCE's of 21.9% and 28.8%, respectively. Encapsulated tandems demonstrated excellent stability under continuous 1 sun illumination for 1000 h and retained 97% of initial PCE after 400 thermal cycles test (between -40 and 85 degrees C), twice the length of the IEC61215 Thermal Cycling test standard. image

Back-contact architectures offer a promising route to improve the record efficiencies of perovskite solar cells (PSCs) by eliminating parasitic light absorption. However, the performance of back-contact PSCs is limited by inadequate carrier diffusion in perovskite. Here, we report that perovskite films with a preferred out-of-plane orientation show improved carrier dynamic properties. With the addition of guanidine thiocyanate, the films exhibit carrier lifetimes and mobilities increased by 3–5 times, leading to diffusion lengths exceeding 7 μm. The enhanced carrier diffusion results from substantial suppression of nonradiative recombination and improves charge collection. Devices using such films achieve reproducible efficiencies reaching 11.2 %, among the best performances for back-contact PSCs. Our findings demonstrate the impact of carrier dynamics on back-contact PSCs and provide the basis for a new route to high-performance back-contact perovskite optoelectronic devices at low cost.

Polydopamine (PDA) is a synthetic model for melanin and has a wide range of opto-electronic properties that underpin its utility in applied and biological settings, from broadband light absorbance to possessing stable free radical species. Here, we show that PDA free radicals are photo-responsive under visible light irradiation, enabling PDA to serve as a photo-redox catalyst. Steady-state and transient electron spin resonance spectroscopy reveals a reversible amplification in semiquinone radical population within PDA under visible light. This photo-response modifies the redox potential of PDA and supports sensitisation of exogenous species via photoinduced electron transfer (PET). We demonstrate the utility of this discovery by employing PDA nanoparticles to photosensitise a common diaryliodonium photoinitiator and initiate free-radical polymerisation (FRP) of vinylic monomers. In situ 1 H nuclear magnetic resonance spectroscopy reveals an interplay between PDA-driven photosensitising and radical quenching during FRP under blue, green, and red light. This work provides crucial insights into the photoactive free radical properties of melanin-like materials and reveals a promising new application for polydopamine as a photosensitiser.

2D Perovskites Cs2Pb(SCN)2Br2, an inorganic-cation pseudo-halide 2D phase perovskite single crystal, is grown by a simple antisolvent vapor-assisted crystallization method, as reported by Chu-Chen Chueh, Anita W. Y. Ho-Baillie, and co-workers in article number 2104782. Cs2Pb(SCN)2Br2 exhibits a reversible first-order phase transformation to CsPbBr2 at 450 K and has a low exciton binding energy amongst the 2D perovskites. Demonstration for photodetector application shows respectable responsivity and detectivity.

Modifying surfaces using free radical polymerization (FRP) offers a means to incorporate the diverse physicochemical properties of vinyl polymers onto new materials. Here, we harness the universal surface attachment of polydopamine (PDA) to "prime" a range of different surfaces for free radical polymer attachment, including glass, cotton, paper, sponge, and stainless steel. We show that the intrinsic free radical species present in PDA can serve as an anchor point for subsequent attachment of propagating vinyl polymer macroradicals through radical-radical coupling. Leveraging a straightforward, twofold soak-wash protocol, FRP over the PDA-functionalized surfaces results in covalent polymer attachment on both porous and nonporous substrates, imparting new properties to the functionalized materials, including enhanced hydrophobicity, fluorescence, or temperature responsiveness. Our strategy is then extended to covalently incorporate PDA nanoparticles into organo-/hydrogels via radical cross-linking, yielding tunable PDA-polymer composite networks. The propensity of PDA free radicals to quench FRP is studied using in situ 1H nuclear magnetic resonance and electron paramagnetic resonance spectroscopy, revealing a surface area-dependent macroradical scavenging mechanism that underpins PDA-polymer conjugation. By combining the arbitrary surface attachment of PDA with the broad physicochemical properties of vinyl polymers, our strategy provides a straightforward route for imparting unlimited new functionality to practically any surface.

Solar cells based on GaAs often include a wide-bandgap semiconductor as a window layer to improve surface passivation. Such devices often have poor photon-to-electron conversion efficiency at higher photon energies due to parasitic absorption. In this article, we deposit FAPbBr3 perovskite quantum dots on the AlInP window layer of a GaAs thin-film solar cell to improve the external quantum efficiency (EQE) across its entire absorption range, resulting in an 18% relative enhancement of the short-circuit current density. Luminescent downshifting from the quantum dots to the GaAs device contributes to a large effective enhancement of the internal quantum efficiency (IQE) at shorter wavelengths. Additionally, improved surface passivation of the window layer results in a 14–16% broadband increase of the IQE. These mechanisms combined with increased overall photon collection (antireflective effects) results in a doubling of the EQE in the ultraviolet region of the solar spectrum. Our results show a promising application of perovskite nanocrystals to improve the performance of well-established thin-film solar cell technologies.