The high conversion efficiency has made metal halide perovskite solar cells a real breakthrough in thin film photovoltaic technology in recent years. Here, we introduce a straightforward strategy to reduce the level of electronic defects present at the interface between the perovskite film and the hole transport layer by treating the perovskite surface with different types of ammonium salts, namely ethylammonium, imidazolium and guanidinium iodide. We use a triple cation perovskite formulation containing primarily formamidinium and small amounts of cesium and methylammonium. We find that this treatment boosts the power conversion efficiency from 20.5% for the control to 22.3%, 22.1%, and 21.0% for the devices treated with ethylammonium, imidazolium and guanidinium iodide, respectively. Best performing devices showed a loss in efficiency of only 5% under full sunlight intensity with maximum power tracking for 550 h. We apply 2D- solid-state NMR to unravel the atomic-level mechanism of this passivation effect.

Lead halide perovskites have emerged as promising materials for light-emitting devices. Here, we report the preparation of colloidal CsPbBr3 nanoplatelets (3 × 4 × 23 nm3) experiencing a strong quasi-one-dimensional quantum confinement. Ultrafast transient absorption and broadband fluorescence up-conversion spectroscopies were employed to scrutinize the carrier and quasiparticle dynamics and to obtain a full description of the spectroscopic properties of the material. An exciton binding energy of 350 meV, an absorption cross section at 3.2 eV of 5.0 ± 0.3 × 10–15 cm–2, an efficient biexciton Auger recombination lifetime of 9 ± 1 ps, and a biexciton binding energy of 74 ± 4 meV were determined. Moreover, a short-lived emission from hot excitons was observed, which is related to the formation of band-edge excitons. The time constant of both processes is 300 ± 50 fs. These results show that CsPbBr3 nanoplatelets are indeed quite promising for light-emitting technological applications.

Evidence for an ultrafast light-induced cascade of energy and charge transfer between aggregated quantum-confined nanoplatelets and nanoparticles of CH3NH3PbBr3 perovskite.

Flavin-binding fluorescent proteins (FbFPs) are a class of fluorescent reporters that have been increasingly used as reporters in the study of cellular structures and dynamics. Flavin's intrinsic high singlet oxygen ((1)O2) quantum yield (ΦΔ = 0.51) provides a basis for the development of new FbFP mutants capable of photosensitising (1)O2 for mechanistic and therapeutic applications, as recently exemplified by the FbFP miniSOG. In the present work we report an investigation on the (1)O2 photoproduction by Pp2FbFP L30M, a novel derivative of Pseudomonas putida Pp2FbFP. Direct detection of (1)O2 through its phosphorescence at 1275 nm yielded the value ΦΔ = 0.09 ± 0.01, which is the highest (1)O2 quantum yield reported to date for any FP and is approximately 3-fold higher than the ΦΔ for miniSOG. Unlike miniSOG, transient absorption measurements revealed the existence of two independent triplet states each with a different ability to sensitise (1)O2.