Interface engineering through passivating agents, in the form of organic molecules, is a powerful strategy to enhance the performance of perovskite solar cells. Despite its pivotal function in the development of a rational device optimization, the actual role played by the incorporation of interfacial modifications and the interface physics therein remains poorly understood. Here, we investigate the interface and device physics, quantifying charge recombination and charge losses in state-of-the-art inverted solar cells with power conversion efficiency beyond 23% - among the highest reported so far - by using multidimensional photoluminescence imaging. By doing that we extract physical parameters such as quasi-Fermi level splitting (QFLS) and Urbach energy enabling us to assess that the main passivation mechanism affects the perovskite/PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) interface rather than surface defects. In this work, by linking optical, electrical measurements and modelling we highlight the benefits of organic passivation, made in this case by phenylethylammonium (PEAI) based cations, in maximising all the photovoltaic figures of merit.

We employ flash IR annealing to investigate the phase transition of formamidinium lead tridiode (FAPbI3) thin-films for their solar cell application. Measuring the enthalpy changes of FAPbI3 composition under different...

The investigation of chemical and optoelectronic properties of halide perovskite layers and associated interfaces is crucial to harness the full potential of perovskite solar cells. Depth-profiling photoemission spectroscopy is a primary tool to study the chemical properties of halide perovskite layers at different scales from the surface to the bulk. The technique employs ionic argon beam thinning that provides accurate layer thicknesses. However, there is an urgent need to corroborate the reliability of data on chemical properties of halide perovskite thin films to better assess their stability. The present study addresses the question of the Ar+ sputtering thinning on the surface chemical composition and the optoelectronic properties of the triple-cation mixed-halide perovskite by combining X-ray photoemission spectroscopy (XPS) and photoluminescence (PL) spectroscopy. First, XPS profiling is performed by Ar+ beam sputtering on a half-cell: glass/FTO/c-TiO2/perovskite. The resulting profiles show a very homogeneous and reproducible element distribution until near the buried interface; therefore, the layer is considered as quasihomogeneous all over its thickness, and the sputtering process is stable. Second, we evaluated a set of thinned perovskite layers representative of selected steps along the profile by means of PL imaging optical measurements in both steady-state and transient regimes to assess possible perturbation of the optical properties from the surface to bulk. Obtained PL spectra inside the resulting craters show no peak shift nor phase segregation. Accordingly, the transient PL measurements do not reveal any changes of the surface recombination rate in the sputtered areas. This demonstrates that there is no cumulative effect of sputtering nor drastic chemical and optoelectronic modifications, validating the determination of the in-depth composition of the perovskite layer. Combining XPS profiling with PL characterization can be a precise tool to be applied for an extensive study of the multiple layers and mixed organic/inorganic interfaces of photovoltaic devices.

Hybrid mixed halide perovskites are endowed with relatively high ionic motion and low electron mobility, which is surprising considering the high photovoltaic conversion efficiency they can allow. Here, we study electronic and ionic transport in hybrid mixed halide perovskites (MA,FA)­Pb­(I,Br)3 using multidimensional luminescence imaging such as time-resolved and spectrally resolved imaging techniques. At short time scale (<1 μs) under pulsed electric bias, we could distinguish electron and hole transport using PL images in a situation where ion migration can be neglected. This resulted in the measurement of a 2-fold higher mobility for holes. At longer time (>1s) we observe the slower migration of ions that induces bandgap narrowing and defects creation, which we relate to halide accumulation at the positive electrode. The observed phenomena are relevant for perovskite-based PV and LED devices.

The excellent optoelectronic and transport properties of halide perovskites led to a rapid development of perovskite based optoelectronic devices. The fundamental understanding of charge carrier dynamics as well as the implementation of physical models able to accurately describe their behaviour are essential for further improvements in the field. Here, combining advanced modeling and characterization, a method for analyzing the short time dynamics of time resolved fluorescence imaging (TR-FLIM) decays is demonstrated. A theoretical scaling law for the time derivative of transient photoluminescence decays as a function of the excitation power is extracted. This scaling law, computed from classical drift-diffusion equations, defines an innovative and simple way to extract quantitative values for several transport parameters including the external radiative recombination coefficient. The model was notably applied on a set of images acquired with a temporal shift of 250 ps to map the top surface recombination velocity of a triple cation mixed halide perovskite thin film at the microscale. The development of high-time-resolution imaging techniques coupled with the scaling method for analyzing short-time dynamics provides a solid platform for the investigation of local heterogeneities in semiconductor materials and the accurate determination of the main parameters governing their carrier transport. I. INTRODUCTIONOver the last decade, lead-halide perovskites solar cells have proved to be a serious candidate for reaching large scale photovoltaic (PV) solar energy conversion, a much-needed solution to meet climate targets and move towards a low-carbon economy. However, despite this emerging technology has recently reached a record power conversion efficiency of 25.5% for a single junction device [1,2], several open questions persist in the scientific community, ranging from the nature and densities of the defects in the absorbers [3-5], the optimal design for the interfaces energetics in a full device [6,7], and the long term stability [7][8][9].The optimization of device performances goes along with the complete understanding of complex recombination processes occurring both in the bulk and at the interfaces. Due to the interplay of several chemical and physical parameters in these hybrid compounds, such