This paper reports the first use of an amide-based hole transport material in a solid-state dye-sensitised solar cell. A substantial improvement in solar cell efficiency from 0.04 to 2.26% was achieved through prolonged oxidation in air and light soaking for the amide-based hole-transporting mediator, TPABT. Time-resolved spectroscopic studies show that the oxidation state and additive concentration alter the charge-transfer and regeneration kinetics, which are consistent with the time-dependent changes in device properties. Our study shows that, if the oxidation state and doping are carefully controlled, TPABT-based hole transport materials could serve as a viable, cost-effective alternative to Spiro-OMeTAD, the conventional yet expensive hole-transporting material widely used in emerging photovoltaics.

Precise control of solid-state fluorescence through molecular design is central to the development of advanced functional materials for sensing, imaging, and optical information storage. In particular, aggregation-induced emission (AIE) and...

Self-assembled monolayer (SAM) hole transport layers are commonly used in state-of-the-art perovskite single-and multi-junction solar cells. Their precursor molecules are prone to aggregation. We report SAM-solution-pH-modulation that effectively suppresses aggregation, improving deposited film quality. We designed and synthesized a novel material, 6-aminohexylphosphonic acid hydrochloride (6AHPACl), to be added to the (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) solution as part of a co-SAM strategy. Apart from the advantage of pH modulation, the inclusion of 6AHPACl improved SAM anchoring, SAM/perovskite interface energetics, and wettability of the overlaying perovskite layer and therefore its quality. This co-SAM strategy enabled demonstrations of a wide-band gap (1.67 eV) perovskite cell producing a champion efficiency of 22.8% and a 1 cm2 monolithic perovskite-silicon double junction cell producing a certified efficiency of 29.1%. An encapsulated device retained 95% of its efficiency after 1,010 thermal cycles (-40 degrees C to 85 degrees C). Another encapsulated double junction device surpassed the International Electrotechnical Commission (IEC) 61215 humidity freeze test.

Organic hole-transporting materials (HTMs) play a key role in enhancing both the efficiency and endurance of photovoltaic devices and for optoelectronic applications. In contrast to their inorganic counterparts, they offer distinct advantages such as solution processability, tunable properties, and low-cost fabrication. However, their electrical conductivity in most cases is intrinsically low and can be enhanced through doping using chemical oxidants. Doping typically involves the partial oxidation of the HTM, generating additional free charges and improved film conductivity. In this work, we investigate the effect of molecular design on the doping mechanism, with a specific focus on imine-linked, triarylamine-based compounds. Our research indicates that the effectiveness of doping and resulting conductivity are determined by the energy of the dopant-HTM complex. Through a combined approach including density functional theory (DFT) modelling, spectroscopy, and conductivity measurements, we observe that oxidation of the HTM does not guarantee doping if the generated charges are not free. This highlights the importance of imine bond orientation in the stabilisation of generated holes. Interestingly, a seemingly trivial chemical change, such as the inversion of an imine bond affects the doping of the material. Our findings show that such isomerisation can result in charge transfer complexes with stabilised holes that do not improve conductivity. This challenges many common approaches to chemical doping, where standard additives are added to newly developed HTMs without prior investigation of their efficacy for the chemical system being studied. We advocate for a tailored understanding of the doping mechanism and the use of spectroscopic techniques to enhance HTM design and characterisation.

The incorporation of Ruddlesden–Popper (RP)/3D perovskite heterostructures into photovoltaic cells has been shown to increase both the efficiency and stability of the devices. Here, a series of methylammonium lead triiodide (MAPbI 3 ) thin films treated with varying 2‐phenylethylammonium (PEA) concentrations are investigated with static and ultrafast spectroscopic techniques to reveal the mechanisms of the observed performance benefits. Transient absorption spectroscopy is employed to elucidate the effect of a surface RP layer on the excited state of the MAPbI 3 films and reveal that several different RP structures are formed and participate in the charge‐carrier dynamics. The passivation effects of PEA are investigated with optical pump–terahertz probe (OPTP) experiments using a variety of excitation conditions to simultaneously probe the surface and bulk recombination dynamics. Fitting models to the OPTP data for each excitation scheme allows the material parameters that govern the ultrafast dynamics to be quantified. It is found that as the PEA concentration increases, the surface recombination velocity exhibits a monotonic decrease, suggesting the RP layer is effective at passivating surface traps. Furthermore, the bulk monomolecular recombination rate is also found to decrease with the addition of PEA, indicating that the benefits of this passivation approach are not limited to the upper surface of the MAPbI 3 films.

Utilizing layered perovskites (LPKs) to passivate the surface of perovskite materials is a successful strategy that currently yields state-of-the-art record-breaking devices. Nevertheless, it is not clear what happens to the LPK once other layers are processed on top. Furthermore, these LPKs can provide benefits in both p-type-intrinsic-n-type (P-I-N) and its inverted n-type-intrinsic-p-type (N-I-P) perovskite solar cell configuration, despite significant differences in their processing. In this work, we propose that this occurs due to a convergent optimization pathway, due to the thinning down and dissolution of the LPK during the deposition of subsequent layers. Here, we use X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) to demonstrate that for most of the “processing window” employed in the literature, the LPK is severely disrupted by the deposition of charge extraction layers. Indeed, the observation of highly crystalline layers via XRD correlates with a significant reduction in short-circuit current in solar cells, counteracting any other benefits.

Thermal processing is widely used in solution‐based coating techniques or to enhance solubility, yet the impact on supramolecular self‐assembly and thin film properties remains largely unexplored. Here, we demonstrate how heating and cooling cycles modulate the self‐assembly of amino acid‐appended perylene bisimides (PBIs), influencing their structural and optoelectronic properties. Using small‐angle neutron scattering (SANS), rheology, and absorption spectroscopy, we show that heating increases fibre flexibility while cooling results in spherical aggregate formation. Additionally, we demonstrate the impact of these changes on thin film performance using nanoindentation and voltammetry. When incorporated as electron transport layers (ETLs) in perovskite solar cells, heat‐cooling reduces the series resistance from 6.33 to 4.40 Ω∙cm 2 , enhancing device efficiency. Our findings highlight the importance of thermal history in supramolecular materials and emphasise the need for strict temperature control in solution‐based coating techniques to optimise optoelectronic device performance.

Self-assembled molecules (SAMs) are widely used as hole-selective contacts in perovskite solar cells (PSCs). They are traditionally designed to facilitate charge injection by aligning their highest occupied molecular orbital (HOMO) with the perovskite's valence band. However, interfacial energy barriers may not necessarily hinder performance, and in some cases, can boost the devices' open-circuit voltage, thereby improving efficiency. This raises an important question: is injection through the SAM, to promote charge extraction, a necessary or even desirable criterion? To investigate this, we compare two Spiro-OMeTAD derivatives: Spiro-A, which is directly attached to the indium-doped tin oxide (ITO) anode by a carboxylic acid moiety, forcing the HOMO level to be in close proximity to the ITO, and Spiro-B, which incorporates a spacer group to separate the HOMO from ITO spatially. Contrary to expectations, Spiro-B achieves a higher open-circuit voltage (VOC) and power conversion efficiency (PCE) than Spiro-A despite having a lower built-in potential (VBI). Stabilise and pulse (SaP) measurements confirm that Spiro-B promotes charge accumulation by reducing interfacial recombination, thus increasing quasi-Fermi level splitting (QFLS). Furthermore, the carbazole-based reference SAM (Me-4PACz) achieves the highest VOC, demonstrating that direct charge injection is not always beneficial. These results challenge conventional molecular design strategies, emphasising the importance of controlling interfacial recombination over maximising charge injection. This work provides new insights for optimising SAMs in PSCs, offering a pathway toward higher efficiency through tailored energy barriers and charge accumulation dynamics.

Interface engineering is a powerful tool for enhancing electron/hole transfer and extraction, as well as reducing charge carrier recombination in perovskite-based optoelectronic devices, including light-emitting diodes (LEDs) and photovoltaic (PV) devices. Here, incorporating an interlayer between the perovskite and charge transport layers has been an extremely successful approach to fine-tune energy level alignment, boosting device performance. In this work, we investigate the incorporation of bismuth-based perovskitoids as interlayers to deepen the position of the perovskite's conduction band. Our results clearly show that perovskite solar cells based on a PIN architecture with a triple-cation composition (TC) incorporating the bismuth-based interlayer outperform those without when using C60-fullerene (C60) as the electron charge extraction layer. We attribute this improvement to the deepening of the conduction band position by approximately 0.5 eV, which agrees with the X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements. These findings demonstrate the potential of Bi-based perovskitoid as interlayers to induce band bending in the perovskite layer, effectively allowing fine-tuning of the energy level alignment at the device interfaces, thereby paving the way for future optoelectronic technologies.

To address the suboptimal charge transfer and recombination losses at perovskite/ Phenyl-C61-butyricacidmethylester (PCBM) interface in inverted perovskite solar cells (PSCs), a fullerene derivative interlayer is introduced, which can passivate the defects at the perovskite surface via interactions with the phosphonic acid group, while the fullerene part of the molecule interacts with PCBM and ensures efficient charge transfer. The use of 4-(1 ',5 '-Dihydro-1 '-methyl-2 ' H-[5,6]fullereno-C60-Ih-[1,9-c]pyrrol-2 '-yl)phenylphosphonic acid (CPPA) interlayer results in significant shortening of charge carrier lifetime indicating improved charge extraction, which leads to as significant enhancement of power conversion efficiency (PCE) for both CsFA (from 22.8% to 24.6%) and CsFAMA (from 22.1% to 25.1%) PSCs. The observed improvement can be attributed to the synergistic effects of the phosphonic acid and fullerene in CPPA molecule, as benzylphosphonic acid interfacial layers yields significantly smaller changes in charge carrier lifetime and device performance. The CPPA interlayer also results in enhanced stability, with CPPA-containing devices retaining 90% of the initial PCE after 2000 h in the dark in ambient without encapsulation, while encapsulated devices retain 89% of the initial value after 1000 h of MPP testing under 1 Sun illumination, as well as exhibit stable performance outdoors under ambient sunlight for 112 days.

Achieving effective doping in n-type organic molecular charge transport materials is critical for the development of high-performance optoelectronic devices. However, the role of side-chains in doping reactions remains incompletely understood in some systems. This study focuses on naphthalenediimide (NDI) derivatives, which offer simple synthetic protocols and potentially lower costs compared to traditional fullerene-derived materials. In particular, we explore two functionalised NDI derivatives, comparing one with polar ethylene glycol side-chains (NDI-G) to a non-polar variant with branched alkyl side-chains (NDI-EtHx). Our results show that the effectiveness and speed of the doping reaction with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) is much higher with the more polar NDI-G derivative. We postulate that this arises partly from the closer interactions between the dopant and the NDI molecule, facilitated by the polar glycol side-chains. As a result, thin films reach conductivities exceeding 10-2 S cm-1. We additionally demonstrate their incorporation into efficient perovskite solar cells, demonstrating the effectiveness of the doping process. We investigate this process with a combination of spectroscopy and density functional theory (DFT) modelling, showing that a complex is likely formed between the resulting N-DMBI cation and the NDI radical anion which then promotes electron transfer to a neutral NDI molecule, thereby generating free charge in the film. These findings underscore the importance of synthetic design on the doping behaviour, with the incorporation of ethylene glycol side-chains emerging as an effective strategy to achieve better electrical conductivity for NDI based systems.

Chemiresitive sensing allows the affordable and facile detection of small molecules such as H2O and CO2. Herein, we report a novel class of Earth-abundant post transition metal substituted Keggin polyoxometalates (POMs) for chemiresistive sensing applications, with conductivities up to 0.01 S cm-1 under 100% CO2 and 65% Relative Humidity (RH).

Surface treatment of perovskite materials with their layered counterparts has become an ubiquitous strategy for maximizing device performance. While layered materials confer great benefits to the longevity and long‐term efficiency of the resulting device stack via passivation of defects and surface traps, numerous reports have previously demonstrated that these materials evolve under exposure to light and humidity, suggesting that they are not fully stable. Therefore, it is crucial to study the behavior of these materials in isolation and in conditions mimicking a device stack. Here, it is shown that perovskite capping layers templated by a range of cations on top of methylammonium lead iodide devolve in conditions commonly found during perovskite fabrication, such as exposure to light, solvent, and moisture. Photophysical, structural, and morphological studies are used to show that the degradation of these layered perovskites occurs via a self‐limiting, pinhole‐mediated mechanism. This results in the loss of whole perovskite sheets, from a few monolayers to tens of nanometers of material, until the system stabilizes again as demonstrated for exfoliated flakes of PEA2PbI4. This means that initially targeted structures may have devolved, with clear optimization implications for device fabrication.

Interest in sustainable and bio-inspired materials for optoelectronic applications is burgeoning, driven by the prospect of greener production, compatibility with large-scale manufacturing and potential biocompatibility. This study introduces two analogues of the biological redox co-factor flavin (BFG, BFA) as bioinspired electron-transporting materials featuring solubilizing ethylene glycol and alkyl side chains. These materials demonstrated a conductivity of similar to 5.6 x 10-7 S cm-1 in their pristine form which compares favourably with widely employed PCBM (6.8 x 10-8 S cm-1). To enhance the conductivity of the material the chemical dopant N-DMBI was added. UV-vis absorption and electron spin resonance measurements confirmed radical anion formation, while glycol-functionalized derivative BFG shows faster reactivity toward the dopant due to increased polarity of the acceptor molecule conferred by the more polar side chain. Surprisingly, these materials did not exhibit the expected enhancement effect in terms of conductivity or increased power conversion efficiency in perovskite solar cells. DFT calculations correlated to features in the absorption spectra of the compounds indicates the formation of stable charge-transfer complexes upon the addition of the dopant. We hypothesise that this inhibits electron transfer of the reduced species in the film to its undoped neighbour and thereby prevents effective doping. Our results highlight the significance of charge-transfer complexation in the design of future electron transporting materials for perovskite solar cells and advocates the use of low cost DFT modelling early on in the design of these species and their dopants.

Improved knowledge of the influence of temperature upon layered perovskites is essential to enable perovskite-based devices to operate over a broad temperature range and to elucidate the impact of structural changes upon the optoelectronic properties. We examined the Ruddlesden-Popper layered perovskite 2-thiophenemethylammonium lead iodide (ThMA(2)PbI(4)) and observed a structural phase transition between a high- and a low-temperature phase at 220 K using temperature-dependent X-ray diffraction, UV-visible absorption, and photoluminescence (PL) spectroscopy. The structural phase transition altered the tilt pattern of the inorganic octahedra layer, modifying the absorption and PL spectra. Further, we found a narrow and intense additional PL peak in the low-temperature phase, which we assigned to radiative emission from a defect-bound exciton state. In both phases we determined the thermal expansion coefficient and found values similar to those of cubic 3D perovskites, i.e., larger than those of typical substrates such as glass. These results demonstrate that the organic spacer plays a critical role in controlling the temperature-dependent structural and optoelectronic properties of layered perovskites and suggests more widely that strain management strategies may be needed to fully utilize layered perovskites in device applications.

Semiconductor core optical fibers are highly desirable for fiber-based photonic and optoelectronic applications as they can combine strong optical nonlinearities, tight light confinement, wide transmission bands, and electronic functionality within a single platform. Perovskites have emerged as particularly exciting materials for semiconductor photonics as they have strong optical nonlinearities and tunable optoelectronic bandgaps. However, lead-based perovskites contain toxic elements and are, therefore, not environmentally friendly. Furthermore, in fiber form, their core-size is prohibitively large, making them unsuitable for nonlinear optics and applications that require single-mode guidance, such as telecommunications. Here, we report a metal-free perovskite core optical fiber where lead has been substituted for an ammonium cation in the perovskite structure. The core material has a wide bandgap greater than 5 eV, a high laser damage threshold, and a core diameter that can be produced as small as 5 µm. At this core size, the fiber supports just six modes, and the fundamental mode can readily be excited and isolated. Moreover, the metal-free perovskite has a second-order susceptibility that is absent in the archetypal lead-based perovskites and many other semiconductor core materials, such as silicon and germanium. The second-order susceptibility is important for many nonlinear optics applications, such as second-harmonic generation and quantum optics.

Grain size and orientation's impact on charge carriers is explored via a new solvent engineering method for MAPbI 3 solar cells. Drift-diffusion simulations connect s-shaped JV curves to slower ions.

Completing the picture of the underlying physics of perovskite solar cell interfaces that incorporate self-assembled molecular layers (SAMs) will accelerate further progress in p-i-n devices. In this work, we modified the Fermi level of a nickel oxide-perovskite interface by utilizing SAM layers with a range of dipole strengths to establish the link between the resulting shift of the built-in potential of the solar cell and the device parameters. To achieve this, we fabricated a series of high-efficiency perovskite solar cells with no hysteresis and characterized them through stabilize and pulse (SaP), JV curve, and time-resolved photoluminescence (TRPL) measurements. Our results unambiguously show that the potential drop across the perovskite layer (in the range of 0.6-1 V) exceeds the work function difference at the device's electrodes. These extracted potential drop values directly correlate to work function differences in the adjacent transport layers, thus demonstrating that their Fermi level difference entirely drives the built-in potential in this device configuration. Additionally, we find that selecting a SAM with a deep HOMO level can result in charge accumulation at the interface, leading to reduced current flow. Our findings provide insights into the device physics of p-i-n perovskite solar cells, highlighting the importance of interfacial energetics on device performance.