Semitransparent efficient methylammonium lead iodide perovskite based solar cells.

Within the most mesmerizing materials in the world of optoelectronics, mixed halide perovskites (MHP) have been distinguished due to the tunability of their optoelectronic properties, balancing both the light harvesting efficiency and charge extraction into highly efficient solar devices. This feature has drawn the attention of analogous hot-topics as photocatalysis for carrying out more efficiently the degradation of organic compounds. However, the photo-oxidation ability of perovskite does not only depend on its excellent light-harvesting properties, but also on the surface chemical environment provided during its synthesis. Accordingly, we studied the role of surface chemical states of MHP based nanocrystals (NCs) synthesized by hot-injection (H-I) and anion-exchange (A-E) approaches, on their photocatalytic (PC) activity for the oxidation of β-naphthol as a model system. We concluded that iodide vacancies are the main surface chemical states that facilitate the formation of superoxide ions, O 2 •─ , responsible for the PC activity in A-E-MHP. Conversely, the PC performance of H-I-MHP is related to the appropriate balance between band gap and a highly oxidizing valence band. This work offers new insights on the surface properties of MHP related to their catalytic activity in photochemical applications.

Fabrication of solution-processed perovskite solar cells (PSCs) requires the deposition of high quality films from precursor inks. Frequently, buffer layers of PSCs are formed from dispersions of metal oxide nanoparticles (NPs). Therefore, the development of trustable methods for the preparation of stable colloidal NPs dispersions is crucial. In this work, a novel approach to form very compact semiconducting buffer layers with suitable optoelectronic properties is presented through a self-functionalization process of the nanocrystalline particles by their own amorphous phase and without adding any other inorganic or organic functionalization component or surfactant. Such interconnecting amorphous phase composed by residual nitrate, hydroxide, and sodium ions, proved to be fundamental to reach stable colloidal dispersions and contribute to assemble the separate crystalline nickel oxide NPs in the final film, resulting in a very homogeneous and compact layer. A proposed mechanism behind the great stabilization of the nanoparticles is exposed. At the end, the self-functionalized nickel oxide layer exhibited high optoelectronic properties enabling perovskite p-i-n solar cells as efficient as 16.6% demonstrating the pertinence of the presented strategy to obtain high quality buffer layers processed in solution at room temperature.

Conjugated oligomers based on fluorene, fluorenone and thiophene derivatives have been prepared by parallel synthesis using the Suzuki cross-coupling reaction. These oligomers can be used as models of the corresponding fluorene copolymers and their structures were correlated with the observed optical and electrochemical behaviour. The long wavelength absorption bands observed for oligomers that contain fluorenone or cyclopentadithiophene units were assigned to an allowed p-p* transition associated with the carbonyl containing monomer unit. In addition the photoluminescence efficiency and the concentration dependence of the long wavelength emission band (.525 nm) for these materials strongly suggests that it can be attributed to emission involving fluorenone-based excimers.