Photon upconversion via triplet–triplet annihilation (TTA-UC) is a promising strategy for increasing maximum theoretical solar cell efficiencies by a factor of 1.3. However, one factor limiting integrated TTA-UC solar cell performance is the transmission window between sensitizer and acceptor molecule absorption. Here we demonstrate that the incorporation of a singlet sensitizer (SS) into a self-assembled trilayer is an effective means of harnessing that previously transmitted light. A record TTA-UC photocurrent density of 0.315 mA cm–2 under 1 sun irradiation was achieved and is attributed to directional SS-to-sensitizer singlet energy transfer and sensitizer-to-acceptor triplet energy transfer, followed by TTA, excited-state electron transfer into TiO2, and regeneration by a redox mediator in solution. These results demonstrate that singlet sensitization-enhanced self-assembled trilayers are a promising strategy for enhancing broad-band light absorption and improving the performance of TTA-UC solar cells.

Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N,N‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI3) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI3 thin films to 77.2° for QA coated MAPbI3 thin films. The stability of QA passivated MAPbI3 perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

The interfaces between perovskite and charge transport layers greatly impact the device efficiency and stability of perovskite solar cells (PSCs). Inserting an ultrathin wide-bandgap layer between perovskite and hole transport layers (HTLs) has recently been shown as an effective strategy to enhance device performance. Herein, a small amount of an organic halide salt, N,N′-dimethylethylene-1,2-diammonium iodide, is used to create two-dimensional (2D)−three-dimensional (3D) heterojunctions on MAPbI 3 thin film surfaces by facile solution processing. The formation of an ultrathin wide-band-gap 2D perovskite layer on top of 3D MAPbI 3 changes the morphological and photophysical properties of perovskite thin films, effectively reduces the surface defects, and suppresses the charge recombination in the interfaces between perovskite and HTL. As a result, a power conversion efficiency of ∼20.2%, with an open-circuit voltage of 1.14 V, a short-circuit current density of 22.57 mA cm −2 , and a fill factor of 0.78, is achieved for PSCs with enhanced stability.

Perovskite light-emitting diodes (PeLEDs) have received great attention for their potential as next-generation display technology. While remarkable progress has been achieved in green, red, and near-infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4-fluoro phenethyl ammonium (4FPEA), the band edges of quasi-2D perovskites are tuned without affecting their band gaps. Detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ −0.65 eV for 4FPEA based thin films relative to PEA-based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi-2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.

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Maximizing regeneration and minimizing recombination rates at dye–semiconductor interfaces is crucial for the realization of efficient dye-sensitized solar and photoelectrosynthesis cells. Previously it has been shown that simply coordinating the metal ion to the nonsurface bound carboxylate groups of a dye molecule can slow recombination rates and increase open-circuit voltages. However, it was unclear if the additional steric effects or charge of the metal ion were the cause of this behavior. Here we use three different redox mediators, (1) I–/I3 –, (2) [tris­(1,10-phenanthroline)­cobalt]3+/2+, and (3) [Co­(4,4′,4″-tritert-butyl-2,2′:6′,2″-terpyridine)­(NCS)3]0/1– to elucidate the role, if any, of electrostatic interactions between the coordinated metal ion and mediator in dictating these interfacial electron transfer events. Using a combination of spectroscopy, electrochemistry, and solar cell measurements, we demonstrate that while electrostatic interactions may influence dye regeneration rates, for example, increased steric bulk of the metal ion between TiO2(e–) and the oxidized mediator likely has a stronger influence on the overall device performance. Additionally, electrochemical impedance spectroscopy and intensity dependent measurements suggest that the coordination of the metal ion can slow diffusion of the mediators within the mesoporous oxide which could have implications for the use of multilayer assemblies in dye-sensitized devices.

In this report, the synthesis and characterization of two bis-cyclometalated iridium(III) complexes are presented. Singlecrystal X-ray diffraction shows that [Ir(ppy) 2 (4,4′-bis-(diethylphosphonomethyl)-2,2′-bipyridine)]PF 6 adopts a pseudooctahedral geometry. The complexes have an absorption feature in the near-visible−UV region and emit green light with excited-state lifetimes in hundreds of nanoseconds. The redox properties of these complexes show reversible behavior for both oxidative and reductive events. [Ir(ppy) 2 (4,4′-bis(phosphonomethyl)-2,2′-bipyridine)]PF 6 readily binds to metal oxide supports, like nanostructured Sn IV -doped In 2 O 3 and TiO 2 , while still retaining reversible redox chemistry. When incorporated as the photoanode in dye-sensitized solar cells, the devices exhibit open-circuit voltages of >1 V, which is a testament to their strength of these iridium(III) complexes as photochemical oxidants.

A simple electrochemical assay to monitor the dispersion of Pseudomonas aeruginosa PA01 biofilm is described. Pyrolytic graphite (PG) electrodes were modified with P. aeruginosa PA01 using layer-by-layer (LbL) methods. The presence of the bacteria on the electrodes was directly monitored using square wave voltammetry (SWV) via the electrochemical reduction of electroactive phenazine compounds expressed by the bacteria, which indicate the presence of biofilm. Upon treatment of bacteria-modified electrodes with a 2-aminoimidazole (2-AI) derivative with known Pseudomonas anti-biofilm properties, the bacteria-related electrochemical reduction peaks decreased in a concentration dependent manner, indicating dispersal of the biofilm on the electrode surface. A similar 2-AI compound with negligible anti-biofilm activity was used as a comparative control and produced muted electrochemical results. Electrochemical responses mirrored previously established bioassay-derived half maximal inhibition concentration (IC50) and half maximal effective concentration (EC50) values.. Biofilm dispersal detection via the electrochemical response was validated by monitoring crystal violet absorbance after its release from electrode confined P. aeruginosa biofilm. Mass spectrometry data showing multiple redox active phenazine compounds are presented to provide insight into the surface reaction complexity. Overall, we present a very simple assay to monitor the anti-biofilm activity of compounds of interest.