Reactive oxygen species (ROS) orchestrate essential signalling pathways, yet bulk dosing with conventional chemical oxidants lacks spatial precision and perturbs the extracellular milieu. Here we exploit organic semiconductor thin films comprising poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) as solid-state, reagent-free photosensitisers that convert dissolved O2 to superoxide at the solid-liquid interface under illumination by visible light. Dihydroethidium fluorimetry quantifies a polymer-loading-dependent ROS flux where films retain full activity after 15 days of incubation under standard cell culture conditions, demonstrating remarkable operational stability. When functionalised with fibronectin, F8T2 films support confluent MCF7 monolayers that are unharmed in the dark yet undergo rapid, light-triggered necrosis, reaching half-maximal viability within 8.8 +/- 3.8 min for 61.4 +/- 19.4 nm thickness films; fibronectin-glass controls show no loss of viability. Mechanical scratching of the polymer film creates ROS-free corridors, demonstrating micron-scale confinement of cytotoxicity to illuminated polymer regions. Since activation is achieved with commodity white LEDs and requires no soluble reagents, "ROS patches" enable spatiotemporally precise oxidative stress for mechanistic redox studies, antimicrobial surface design, and high-throughput screening for ROS-responsive therapeutics.

We combine fluence-dependent photoluminescence (PL) and electrochemical characterization to estimate defect-dependent trapping rates, energetic distributions, and densities of defects, in lead halide perovskite films Cs0.1FA0.9PbI3 and Cs0.17FA0.83Pb(I0.75Br0.25)3, before and after trap passivation with vapor-deposited (3-aminopropyl)trimethoxysilane (APTMS). For both compositions, the PL studies show that energetically shallow subgap near-valence defect densities lead to bimolecular nonradiative recombination which is reduced by 92% after APTMS treatment. Electrochemical characterization of these same active layers shows for the first time that APTMS passivation impacts mainly on near-valence (mobile anionic) defects that decrease in density by 4 orders of magnitude, from 1018 cm-3 to 1014 cm-3, as a result of silane modification. The combination of PL and electrochemical characterization promises a unique approach to speciation and quantification of a broader distribution of trap states in perovskites and provides straightforward assessments of the efficacy of defect mitigation strategies.

Abstract We investigate the nanoscale function of additives used for tin-containing perovskites, using the archetypal FASnI3 (FA = formamidinium). First, we find that the addition of sodium borohydride (NaBH4) is inhomogeneous, with 200–500 nm aggregates forming on the FASnI3 surface. The inhomogeneous distribution of NaBH4 leads to a relatively small (∼1% of the film) amount of reduced perovskite, but the macroscopic properties are dominated by the overwhelming space without any treatment. Upon illumination, more aggregate regions (∼13%) become activated due to reduction of photogenerated I2. On the other hand, when we combine NaBH4 with dipropylammonium iodide (DipI) passivation and illuminate, we observe a much more homogeneous activation effect, which we attribute to denser coverage of NaBH4. We find that the iodine content in FASnI3 films treated with NaBH4 and DipI is 64% less than in those treated with NaBH4 alone. These results underline that the microscale configuration of different additives in tin perovskites is deeply interconnected and it is essential to uncover their chemical reactivity.

Mixed tin-lead (Sn-Pb) halide perovskites, with their tunable bandgaps (1.2-1.4 eV), show great promise for the development of highly efficient all-perovskite tandem solar cells. However, achieving commercial viability and stabilized high efficiency for Sn-Pb perovskite solar cells (PSCs) presents numerous challenges. Among various optimization strategies, the incorporation of additives has proven critical in modulating the crystallization of Sn-Pb perovskites. Despite the widespread use of additives to improve performance, detailed photophysical mechanisms remain unclear. In this work, we elucidate the mechanistic role of guanidinium thiocyanate, a chaotropic agent, in the crystallization of Sn-Pb perovskites. We combine hyperspectral imaging with real-time in situ photoluminescence spectroscopy to study the crystallization process of Sn-Pb perovskites. Our findings reveal that the chaotropic agent modulates the crystal growth rate during perovskite crystallization, resulting in more homogeneous films with reduced nonradiative recombination. We challenge the common assumption that crystallization stops once the solvent evaporates by identifying photoluminescence variations during the cooldown process. The resulting films exhibit a photoluminescence quantum yield of 7.28% and a charge carrier lifetime exceeding 11 μs, leading to a device efficiency of 22.34% and a fill factor of over 80%. This work provides a fundamental understanding of additive-mediated crystal growth and transient cooldown dynamics, advancing the design of high-quality Sn-Pb perovskites for efficient and stable optoelectronics.

In this work, we study the effect of various deposition methods for phosphonic acid interface modifiers commonly pursued as self-assembled monolayers in high-performance metal halide perovskite photovoltaics and light-emitting diodes. We compare the deposition of (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid onto indium tin oxide (ITO) bottom contacts by varying three parameters: the method of deposition, specifically spin coating or prolonged dip coating; ITO surface treatment via HCl/FeCl3 etching; and use in combination with a second modifier, 1,6-hexylenediphosphonic acid. We demonstrate that varying these modification protocols can impact time-resolved photoluminescence carrier lifetimes and quasi-Fermi level splitting of perovskite films deposited onto the phosphonic acid-modified ITO. Ultraviolet photoelectron spectroscopy shows an increase in the effective work function after phosphonic acid modification and clear evidence for photoemission from carbazole functional groups at the ITO surface. We used X-ray photoelectron spectroscopy to probe differences in phosphonic acid coverage on the metal oxide contact and show that perovskite samples grown on ITO with the highest phosphonic acid coverage exhibit the longest carrier lifetimes. Finally, we establish that device performance follows these same trends. These results indicate that the reactivity, heterogeneity, and composition of the bottom contact help to control recombination rates and therefore power conversion efficiencies. ITO etching, prolonged deposition times for phosphonic acids via dip coating, and the use of a secondary, more hydrophilic bisphosphonic acid all contribute to improvements in surface coverage, carrier lifetime, and device efficiency. These improvements each have a positive impact, and we achieve the best results when all three strategies are implemented.

We engineer molecular packing in five derivatives of the nonfullerene acceptor Y6. Using transient absorption spectroscopy, we find evidence of the formation of a delocalized exciton in addition to the local exciton in neat films of the acceptors. Following selective photoexcitation of the acceptors in donor/acceptor blends with D18, we observe anion formation on the same timescale as in neat acceptor films, suggesting that D18 is a bystander to charge generation after photoexcitation of the acceptors. We quantify the recombination kinetics of the delocalized excitons with the monomolecular recombination constant (a) and find that both the hole transfer yield and the internal quantum efficiency in photovoltaic devices increase for acceptor films with lower a. In A1, relatively localized excitons with a limited charge transfer character have fast recombination kinetics (a = 3.2 × 1010 s-1), leading to the lowest IQE (83.7%). In T1, more delocalized excitons with stronger charge transfer character have slower recombination kinetics (a = 5.3 × 109 s-1), leading to a higher IQE (97.2%). Grazing incidence wide-angle X-ray scattering of π-π stacking regions reveals that the tendency to pack face-on is a key driver of exciton delocalization across acceptors with similar molecular packing. We anticipate that this newly identified structural lever will help propel organic photovoltaics toward 20% efficiency.

Abstract Compositional heterogeneity in wide-bandgap (1.8 − 2.1 eV) mixed-halide perovskites is a key bottleneck in the processing of high-quality solution-processed thin films and prevents their application in efficient multijunction solar cells. Notably, mixed-cation (formamidinium-methylammonium) wide-bandgap perovskite films are prone to form micrometer-scale wrinkles which can interfere with the smooth surfaces ideal for multijunction devices. Here, we study the formation dynamics of wrinkled mixed-halide perovskite films and its impact on the local composition and optoelectronic properties. We use in situ X-ray scattering during perovskite film formation to show that crystallization of bromide-rich perovskites precedes that of mixed-halide phases in wrinkled films cast using an antisolvent-based process. Using nanoscopic X­-ray fluorescence and hyperspectral photoluminescence imaging, we also demonstrate the formation of iodide- and bromide-rich phases in the wrinkled domains. This intrinsic spatial halide segregation results in an increased local bandgap variation and Urbach energy. Morphological disorder and compositional heterogeneity also aggravate the formation of sub-bandgap electronic defects, reducing photostability and accelerating light-induced segregation of iodide and bromide ions in thin films and solar cells.

The morphology of quantum dots plays an important role in governing their photophysics. Here, we explore the photoluminescence of spheroidal CsPbBr3 quantum dots synthesized via the room-temperature trioctylphosphine oxide/PbBr2 method. Despite photoluminescence quantum yields nearing 100%, these spheroidal quantum dots exhibit an elongated red photoluminescence tail not observed in typical cubic quantum dots synthesized via hot injection. We explore the origins of this elongated red tail through structural and optical characterization including small-angle X-ray scattering, transmission electron microscopy and time-resolved, steady-state, and single quantum dot photoluminescence. From these measurements we conclude that the red tail originates from emissive traps. We show that treating spheroidal quantum dots with phenethylammonium bromide decreases the line shape asymmetry and increases passivation-consistent with emissive traps due to polar facets.

We show that the use of 1,3-diaminopropane (DAP) as a chemical modifier at the perovskite/electron-transport layer (ETL) interface enhances the power conversion efficiency (PCE) of 1.7 eV band gap mixed-halide perovskite containing formamidinium and Cs single-junction cells, primarily by increasing the open-circuit voltage (VOC) from 1.06 to 1.15 V. We find that adding a postprocessing annealing step after C60 evaporation further improves device performance. Specifically, the fill factor (FF) increases by 20% in the DAP + postannealing devices compared to the control. Using hyperspectral photoluminescence microscopy, we demonstrate that annealing helps improve compositional homogeneity at the electron-transport layer (ETL) and hole-transport layer (HTL) interfaces of the solar cell, which prevents detrimental band gap pinning in the devices and improves C60 adhesion. Using time-of-flight secondary ion mass spectrometry, we show that DAP reacts with formamidinium (FA+) present at the surface of the perovskite structure to form a larger molecular cation, 1,4,5,6-tetrahydropyrimidinium (THP+), which remains at the interface. Combining the use of DAP and annealing the C60 interface, we fabricate Si-perovskite tandems with a PCE of 25.29%, compared to 23.26% for control devices. Our study underscores the critical role of the chemical reactivity of diamines at the surface and the thermal postprocessing of the C60/Lewis-base passivator interface in minimizing device losses and enhancing solar-cell performance of wide-band-gap mixed-cation mixed-halide perovskites for tandem applications.

Efficient delocalization of photo-generated excitons is a key to improving the charge-separation efficiencies in state-of-the-art organic photovoltaic (OPV) absorber. While the delocalization in non-fullerene acceptors has been widely studied, we expand the scope by studying the properties of the conjugated polymer donor D18 on both the material and device levels. Combining optical spectroscopy, X-ray diffraction, and simulation, we show that D18 exhibits stronger π-π interactions and interchain packing compared to classic donor polymers, as well as higher external photoluminescence quantum efficiency (~26%). Using picosecond transient absorption spectroscopy and streak camera photoluminescence measurements, we show that the initial D18 excitons form delocalized intermediates, which decay radiatively with high efficiency in neat films. In single-component OPV cells based on D18, these intermediate excitations can be harvested with an internal quantum efficiency >30%, while in blends with acceptor Y6 they provide a pathway to free charge generation that partially bypasses performance-limiting charge-transfer states at the D18:Y6 interface. Our study demonstrates that donor polymers can be further optimized using similar design strategies that have been successful for non-fullerene acceptors, opening the door to even higher OPV efficiencies.

We use electroabsorption (EA) spectroscopy to probe the charge transfer (CT) character in neat films and blends of donors and acceptors of interest for organic electronic applications. In particular, we compare the CT character in two polymer donor and non-fullerene acceptor blends, including 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IT-4F) and 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6). Like classic polymer/fullerene blends, the blend based on IT-4F exhibits primarily first derivative-like EA features, suggesting localized exciton formation upon photoexcitation. However, the Y6-based blend has an EA spectrum that is dominated by second derivative-like features, consistent with CT character. We show that this signal originates primarily from Y6. We find that Y6 exhibits the highest dipole moment change (7.5 ± 2.5 D) of the molecules that comprise this study, consistent with a high degree of the CT character, and a relatively large polarization volume of 361 ± 70 Å3, consistent with strong electron delocalization. These results point to the origins of exceptional performance of organic photovoltaics (OPVs) based on Y6.

Antisolvent treatment is used in the fabrication of perovskite films to control grain growth during spin coating. We study widely incorporated aromatic hydrocarbons and aprotic ethers, discussing the origin of their performance differences in 2D/3D Sn perovskite (PEA0.2FA0.8SnI3) solar cells. Among the antisolvents that we screen, diisopropyl ether yields the highest power conversion efficiency in solar cells. We use a combination of optical and structural characterization techniques to reveal that this improved performance originates from a higher concentration of 2D phase, distributed evenly throughout the 2D/3D Sn perovskite film, leading to better crystallinity. This redistribution of the 2D phase, as a result of diisopropyl ether antisolvent treatment, has the combined effect of decreasing the Sn4+ defect density and background hole density, leading to devices with improved open-circuit voltage, short-circuit current, and power conversion efficiency.

Drawing from both experimental data and simulation, we highlight best practices for fitting time-resolved photoluminescence (TRPL) decays of halide perovskite semiconductors, which are now widely studied for applications in photovoltaics and light-emitting diodes (LEDs). First, at low excitation intensities, high-quality perovskites often show pseudo-first-order kinetics, consistent with classic minority carrier lifetimes. Second, multiexponential decays, frequently observed at low excitation intensities, often have significant contributions from spatial heterogeneity. We recommend fitting such decays with stretched exponentials, where the stretching factor (beta) can be used to characterize the heterogeneity of the local lifetime distribution. Third, PL decay kinetics can depend on the excitation wavelength. We discuss how penetration depth, carrier diffusion, and surface recombination affect measurements and make recommendations for choosing experimental parameters suited to the question at hand. Accounting for these factors will provide a more reliable and physical interpretation of carrier recombination and better understanding of nonradiative losses in perovskite semiconductors.

We use multimodal microscopy to study carrier recombination in semiconducting tin halide perovskite films based on PEA(0.2)FA(0.8)SnI(3) (PEA = phenethylammonium; FA = formamidinium). We use the observation of pseudo-first-order photoluminescence (PL) decay kinetics to establish a method for quantifying the hole dopant level and nonradiative recombination rate constant. We find that untreated PEA(0.2)FA(0.8)SnI(3) films exhibit large hole doping concentrations of p(0) approximate to 10(19) cm(-3), which is reduced to p(0) approximate to 10(16) cm(-3) after SnF2 treatment. While it is well-known that the radiative recombination rates are increased with p(0), we reveal that the nonradiative rate is also increased. We find that p-type regions in untreated PEA(0.2)FA(0.8)SnI(3) films are centers for nonradiative recombination, which are diminished in films with p(0) approximate to 10(16) cm(-3). We discover significant PL heterogeneity even in PEA(0.2)FA(0.8)SnI(3) films with moderate dopant levels, suggesting that new strategies to eliminate deleterious defects in PEA(0.2)FA(0.8)SnI(3) must be developed.

Organic photovoltaics are remarkably close to reaching a landmark power conversion efficiency of 20%. Given the current urgent concerns regarding climate change, research into renewable energy solutions is crucially important. In this perspective article, we highlight several key aspects of organic photovoltaics, ranging from fundamental understanding to implementation, that need to be addressed to ensure the success of this promising technology. We cover the intriguing ability of some acceptors to undergo efficient charge photogeneration in the absence of an energetic driving force and the effects of the resulting state hybridization. We explore one of the primary loss mechanisms of organic photovoltaics-non-radiative voltage losses-and the influence of the energy gap law. Triplet states are becoming increasingly relevant owing to their presence in even the most efficient non-fullerene blends, and we assess their role as both a loss mechanism and a potential strategy to enhance efficiency. Finally, two ways in which the implementation of organic photovoltaics can be simplified are addressed. The standard bulk heterojunction architecture could be superseded by either single material photovoltaics or sequentially deposited heterojunctions, and the attributes of both are considered. While several important challenges still lie ahead for organic photovoltaics, their future is, indeed, bright.

Blade coating of perovskite solar cells (PSCs) and modules has progressed considerably toward the industrial production of perovskite photovoltaics. Developing stable perovskite precursors is critical for achieving uniform coating over large areas. Here, the engineering of a perovskite precursor solution consisting of 2‐methoxyethanol (2‐Me) and 1,3‐dimethyl‐imidazolidinone (DMI) with superior intermediate phase stability that enables scalable production of efficient perovskite solar modules is reported. With this perovskite precursor solution, uniform and pinhole‐less perovskite film is deposited over a large area of > 100 cm 2 and higher‐efficiency PSCs and modules are obtained. The best‐performing unit cell and module with n‐i‐p configuration reach power conversion efficiencies of 23.4% and 20.1%, respectively. Additionally, a series of non‐destructive metrology methods, such as spectroscopic ellipsometry, hyperspectral photoluminescence, electroluminescence, and laser beam‐induced current mapping, are employed to assess and guide the development the blade‐coated perovskite modules. This results show that rational engineering of precursor inks for blade coating is promising for the scalable production of efficient perovskite solar modules.

We use scanning probe microscopy to study ion migration in formamidinium (FA)-containing halide perovskite semiconductor Cs0.22FA0.78Pb(I0.85Br0.15)3 in the presence and absence of chemical surface passivation. We measure the evolving contact potential difference (CPD) using scanning Kelvin probe microscopy (SKPM) following voltage poling. We find that ion migration leads to a ∼100 mV shift in the CPD of control films after poling with 3 V for only a few seconds. Moreover, we find that ion migration is heterogeneous, with domain interfaces leading to a larger CPD shift than domain interiors. Application of (3-aminopropyl)trimethoxysilane (APTMS) as a surface passivator further leads to 5-fold reduction in the CPD shift from ∼100 to ∼20 mV. We use hyperspectral microscopy to confirm that APTMS-treated perovskite films undergo less photoinduced halide migration than control films. We interpret these results as due to a reduction in the halide vacancy concentration after APTMS passivation.