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Organometallic halide perovskite (MAPPbBr 3 ), Rust-based Vapor Phase Polymerization (RVPP)-PEDOT hole transporting layers and (RVPP-PEDOT)/MAPPbBr 3 dual-layer, deposited on fluorine doped tin oxide glass were studied at room temperature using steady-state absorption, time-resolved photoluminescence imaging and femtosecond time-resolved absorption spectroscopy. Application of these techniques in conjunction with diverse excitation intensities allowed determination of various optoelectronic properties of the perovskite film and the time constant of the hole extraction process. Spectral reconstruction of the bandedge absorption spectrum using Elliot's formula enabled separation of the exciton band. The binding energy of the exciton was determined to be 19 meV and the bandgap energy of the perovskite film was 2.37 eV. Subsequent time-resolved photoluminescence studies of the perovskite film performed using a very weak excitation intensity followed by a global analysis of the data revealed monomolecular recombination dynamics of charge carriers occurring with an amplitude weighted lifetime of 3.2 ns. Femtosecond time-resolved transient absorption of the film performed after excitation intensity spanning a range of over two orders of magnitude enabled determining the rate constant of bimolecular recombination and was found to be 2.6 × 10 −10 cm 3 s −1 . Application of numerous high intensity excitations enabled observation of band filling effect and application of the Burstein–Moss model allowed to determine the reduced effective mass of photoexcited electron–hole pair in MAPPbBr 3 film to be 0.19 rest mass of the electron. Finally, application of transient absorption on RVPP-PEDOT/MAPPbBr 3 enabled determination of a 0.4 ps time constant for the MAPPbBr 3 -to-PEDOT hole extraction process. 

The formation of cyclobutane pyrimidine dimers (CPDs) by a “dark” pathway in melanocytes has been attributed to chemisensitization by dioxetanes produced from peroxynitrite oxidation of melanin or melanin precursors. These dioxetanes are proposed to decompose to triplet state compounds which sensitize CPD formation by triplet–triplet energy transfer. To determine whether such compounds are capable of sensitizing CPD formation, the putative decomposition products of 2,3‐dioxetanes of variously substituted indoles were synthesized and their triplet state energies determined at 77 K. Their ability to photosensitize CPD formation was determined by an enzyme‐coupled gel electrophoresis assay in comparison with norfloxacin (NFX) which has the lowest triplet energy known to sensitize CPD formation. The decomposition products of 2,3‐dioxetanes of 5‐hydroxy and 5,6‐dimethoxy indoles used as models for melanin precursors had lower triplet energies and were incapable of photosensitizing CPD formation. Theoretical calculations suggest that the decomposition products of the 2,3‐dioxetanes of melanin precursors DHI and DHICA will have similarly low triplet energies. Decomposition products of the 2,3‐dioxetanes of indoles lacking oxygen substituents had higher triplet energies than NFX and were capable of photosensitizing CPD formation, suggesting that peroxynitrite oxidation of tryptophan could play a hitherto unrecognized role in the dark pathway to CPDs.

 

While there has been rapid progress in the performance of perovskite solar cells, the details of film formation, effect of processing parameters and perovskite crystal structure are still under discussion. The details of the X-ray diffraction (XRD) pattern of the tetragonal phase of CH 3 NH 3 PbI 3 perovskite existing at room temperature are often overlooked, with unresolved (002) (at 2 θ = 13.99° for CuK α and q = 0.9927 Å −1 ) and (110) (at 2 θ = 14.14° and q = 1.003 Å −1 ) peaks considered to be one peak at 14°, leading to an inaccurate estimation of lattice parameters. In this study, we use an electrospray deposition technique to prepare perovskite films at room temperature, oriented in (002) and (110) directions, with (002) as the preferred orientation. The results of a detailed study on the emergence of the two orientations during perovskite formation are reported. The effect of process parameters, such as substrate temperature during deposition and annealing temperature, on the grain orientation was established using XRD and grazing incidence wide angle X-ray scattering (GIWAXS). The study suggests that an irreversible crystal reorientation from (002) to (110) occurs at high temperature during rapid annealing, whereas a reversible crystal thermal expansion is seen during slow annealing. Finally, the results of the grain reorientation are correlated with the film properties, and it is shown that the film with the dominant (110) orientation has improved morphology and optoelectronic properties. The detailed structural investigation and characterization presented in this study are important for the precise determination of crystal orientation and achievement of desirable photovoltaic properties of the absorber material by carefully observing the adjacent crystal plane peaks in the XRD pattern of the perovskite thin films.