Perovskite-based photovoltaics have been rapidly developed, with record power conversion efficiencies now exceeding 22%. In order to rationally design efficient and stable perovskite solar cells, it is important to understand not only charge trapping and recombination events, but also processes occurring at the perovskite/transport material (TM) interface, such as charge transfer and interfacial recombination. In this work, time-resolved microwave conductivity measurements are performed to investigate these interfacial processes for methylammonium lead iodide and various state-of-the-art organic TMs. A global kinetic model is developed, which accurately describes both the dynamics of excess charges in the perovskite layer and transfer to charge-specific TMs. The authors conclude that for state-of-the-art materials, such as Spiro-OMeTAD and PCBM, the charge extraction efficiency is not significantly affected by intra-band gap traps for trap densities under 1015 cm–3. Finally, the transfer rates to C60, PCBM, EDOT-OMeTPA, and Spiro-OMeTAD are sufficient to outcompete second order recombination under excitation densities representative for illumination by AM1.5.@en

A new concept of the formation of charge transfer (CT) complexes between an intrinsically electron-donating conjugated microporous polymer and a small molecule acceptor is reported. Spirobifluorene-based mesoporous organic polymers with high porosity and Brunauer–Emmett–Teller surface area are synthesized by the Suzuki-coupling reaction of spirobifluorene and pyrene monomers. The simple doping of the synthesized mesoporous, electron-rich, conjugated polymer with 7,7,8,8-tetracyanoquinodimethane as an acceptor leads to efficient CT complexation in the electron-donating mesoporous spaces. This results in a high-speed synthesis (within 5 s), thermally stable compound (up to about 200 °C), and good control of the concentration of donor–acceptor pairs in the CT complex.@en

The concentration dependent luminescence of the SrI2-TmI2 system was investigated. For Tm2+ concentrations up to 5 mol %, the quantum efficiency (QE) of the 2F5/2→2F7/2 emission exhibits a constant value above 50%. The QE drops for higher Tm2+ concentrations, partly due to concentration quenching, as evidenced by a decreasing luminescence lifetime of the 2F5/2→2F7/2 emission, and partly due to the formation of a second crystal phase with CdCl2 structure, in which the 2F5/2→2F7/2 emission is quenched. The temperature and time dependent relaxation dynamics were studied to identify the origin of the limited QE for Tm2+-doping levels below 5 mol %. An anti-correlation between the 5d-4f (3H6,t2g)S=3/2→2F7/2 and 4f-4f 2F5/2→2F7/2 emission intensities was found and rationalised by non-radiative, thermally stimulated, inter-configurational 5d-4f relaxation to the emitting 2F5/2 level of Tm2+. Both, the rise time of the 4f-4f and the decay time of the 5d-4f emission become shorter with increasing temperature. We suggest a similar non-radiative relaxation from the 5d level towards the 2F7/2 ground state to limit the QE below unity. This route becomes more efficient when the 5d (3H6,t2g)S=3/2 state moves closer to the 4f 2F5/2 and 2F7/2 states, which is the case for the CdCl2 phase with a QE close to zero.@en

In this contribution we demonstrate a solid-state approach to triplet-triplet annihilation upconversion for application in a solar cell device in which absorption of near-infrared light is followed by direct electron injection into an inorganic substrate. We use time-resolved microwave photoconductivity experiments to study the injection of electrons into the electron-accepting substrate (TiO2) in a trilayer device consisting of a triplet sensitizer (fluorinated zinc phthalocyanine), triplet acceptor (methyl subsituted perylenediimide), and smooth polycrystalline TiO2. Absorption of light at 700 nm leads to the almost quantitative generation of triplet excited states by intersystem crossing. This is followed by Dexter energy transfer to the triplet acceptor layer where triplet annihilation occurs and concludes by injection of an electron into TiO2 from the upconverted singlet excited state.@en

The red-emitting Sr 2 Si 5 N 8 :Eu 2+ phosphor with a superior quantum efficiency and suitable emission spectrum has been widely used as a promising down-conversion material in white light-emitting diodes. However, its thermal degradation under high temperature handicaps its large scale application, and therefore must be reduced. Here, we proposed to increase the thermal stability of Sr 2 Si 5 N 8 :Eu 2+ by coating a nanometer-order Al 2 O 3 film on each phosphor particle using an atomic layer deposition approach in a fluidized bed reactor. The deposited Al 2 O 3 layer was quite uniform and conformal when using O 3 as the oxidizer, and its thickness could be controlled by the dosage type, deposition temperature and cycle numbers, which largely affects the photoluminescence properties and thermal degradation of the title phosphor. Thermal gravimetric analysis results showed that the oxidation temperature of the coated phosphor increased from 700 to 850 °C, suggesting that the coating layer has the function of anti-oxidation. Meanwhile, the coated phosphor particle surface became hydrophobic. Consequently, the thermal degradation of phosphor powders in air at 200 °C was greatly reduced and the stability of the fabricated LEDs with coated powders was also improved. Prospectively, the proposed approach provides a new strategy to improve the thermal stability of other phosphors. @en