Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences.

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.

As a continuation of the Direct–Indirect (D-I) model theoretical approach presented in Part I of this publication, concerning the photocatalytic oxidation of organic molecules in contact with TiO2 dispersions, a comparative photooxidation kinetic analysis of three model organic molecules, benzene (BZ) dissolved in acetonitrile (ACN), phenol (PhOH) dissolved in either water or acetonitrile, and formic acid (FA) dissolved in water, is presented to test the applicability of the D-I model under both equilibrium and nonequilibrium adsorption–desorption conditions. A previous analysis involving diffuse reflectance ultraviolet–visible (DRUVS) and Fourier transform infrared (FTIR) spectroscopy, combined with adsorption isotherm plots, shows that BZ chemisorption on the TiO2 surface is not allowed, physisorption being in this case the only possible adsorption mode. In line with D-I model predictions, BZ photooxidation is observed to take place via an adiabatic indirect transfer (IT) mechanism, with the participation of photogenerated terminal −Os •– radicals as oxidizing agents. In contrast, because of their strong chemisorption, FA species dissolved in water are found to be mainly photooxidized via inelastic direct transfer (DT) trapping of photogenerated valence-band free holes (h f +). Finally, when dissolved in water, PhOH chemisorption is not favored because of the strong electronic affinity of water molecules with the TiO2 surface, while chemisorption strength considerably increases when PhOH is dissolved in ACN, as far as the electronic interaction of solvent molecules with the TiO2 surface is negligible. Consequently, as predicted by the D-I model, PhOH dissolved in water is photooxidized via a combination of IT and DT mechanisms, the IT photooxidation rate (v ox IT) being about 1 order of magnitude higher than DT photooxidation rate (v ox DT). In contrast, when ACN is used as solvent, v ox IT remains practically unchanged, while v ox DT increases by about 2 orders of magnitude. These photooxidation results sustain the central D-I model hypothesis that the degree of substrate species interaction with the TiO2 surface is a decisive factor determining the kinetics of photocatalytic reactions. The effect of adsorption–desorption equilibrium rupture on the photooxidation kinetics of dissolved substrate species, predicted by the D-I model, is analyzed for the first time from experimental kinetic data concerning the photooxidation of PhOH dissolved in water under high enough illumination intensity (ρ ≈ 1017 cm–2 s–1).

The important role played in TiO 2 heterogeneous photocatalysis by the two-fold-coordinated TiO 2 surface bridging oxygens (>O s 2− or >OH s −

The photocatalytic oxidation kinetics of organic species in semiconductor (sc) gas phase and liquid semiconductor suspensions, strongly depends on the electronic interaction strength of substrate species with the sc surface. According to the Direct–Indirect (D-I) model, developed as an alternative to the Langmuir–Hinshelwood (L-H) model (Salvador, P. et al. Catalysis Today 2007, 129, 247), when chemisorption of dissolved substrate species is not favored and physisorption is the only existing adsorption mechanism, interfacial hole transfer takes place via an indirect transfer (IT) mechanism, the photo-oxidation rate exponentially depending on the incident photon flux (V ox = V ox IT ∝ ρ n ), with n = 1/2 under high enough photon flux (standard experimental conditions), whatever the dissolved substrate concentration, [(RH2)liq]. In contrast, under simultaneous physisorption and chemisorption of substrate species, hole capture takes place via a combination of an indirect transfer (IT) and a direct transfer (DT) mechanism (V ox = V ox IT + V ox DT), with V ox DT ∝ ρ n and n = 1 for low enough ρ values, as long as adsorption–desorption equilibrium conditions existing in the dark are not broken under illumination, and monotonically decreasing toward n = 0 as ρ increases and adsorption–desorption equilibrium becomes broken. This behavior invalidates the frequently invoked axiom that the reaction order (exponent n) exclusively depends on the photon flux intensity, being in general n = 1 and n = 1/2 under low and high illumination intensity, respectively, independent of the nature of the sc-substrate electronic interaction. On the basis of a detailed analysis of the parameter defined as a = (V ox)2/2[(RH2)liq]ρ, an experimental test able to determine the influence of both interfacial hole transfer mechanisms, DT and IT, in the photo-oxidation kinetics, is presented. A simple method allowing the estimation of the photon flux critical value where adsorption–desorption equilibrium of chemisorbed substrate species is broken and the reaction order starts to decreases from n = 1 toward n = 0, is described.

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Effective control of the interface between the metal cathode and the electron transport layer (ETL) is critical for achieving high performance p-i-n planar heterojunction perovskite solar cells (PSCs). Several organic molecules have been explored as interlayers between the silver (Ag) electrode and the ETL for the improvement in the photovoltaic conversion efficiency (PCE) of p-i-n planar PSCs. However, the role of these organic molecules in the charge transfer at the metal/ETL interface and the chemical degradation processes of PSCs has not yet been fully understood. In this work, we systematically explore the effects of the interfacial modification of the Ag/ETL interface on PSCs using rhodamine 101 as a model molecule. By the insertion of rhodamine 101 as an interlayer between Ag and fullerene derivatives (PC60BM and PC70BM) ETLs improve the PCE as well as the stability of p-i-n planar PSCs. Atomic force microscopy (AFM) characterization reveals that rhodamine passivates the defects at the PCBM layer and reduces the band bending at the PCBM surface. In consequence, charge transfer from the PCBM towards the Ag electrode is enhanced leading to an increased fill factor (FF) resulting in a PCE up to 16.6%. Moreover, rhodamine acts as a permeation barrier hindering the penetration of moisture towards the perovskite layer as well as preventing the chemical interaction of perovskite with the Ag electrode. Interestingly, the work function of the metal cathode remains more stable due to the rhodamine incorporation. Consequently, a better alignment between the quasi-Fermi level of PCBM and the Ag work function is achieved minimizing the energy barrier for charge extraction. This work contributes to reveal the relevance of proper interfacial engineering at the metal-cathode/organic-semiconductor interface.

TiO2 surface lattice oxygens are actively involved in the photocatalytic oxidation of water as demonstrated by isotopic tracing experiments with Ti18O2.