Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.

Interface engineering of organic-inorganic halide perovskite solar cells (PSCs) plays a pivotal role in achieving high power conversion efficiency (PCE). In fact, perovskite photoactive layer needs to work synergistically with the other functional components of the cell, such as charge transporting/active buffer layers and electrodes. In this context, graphene and related twodimensional materials (GRMs) are promising candidates to tune "on demand" the interface properties of PSCs. In this work, we fully exploit the potential of GRMs by controlling the optoelectronic properties of hybrids between molybdenum disulfide (MoS2) and reduced graphene oxide (RGO) as hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3)-based PSC. We show that zero-dimensional MoS2 quantum dots (MoS2 QDs), derived by liquid phase exfoliated MoS2 flakes, provide both holeextraction and electron-blocking properties. In fact, on the one hand, intrinsic n-type doping-induced intra-band gap states effectively extract the holes through an electron injection mechanism. On the other hand, quantum confinement effects increase the optical band gap of MoS2 (from 1.4 eV for the flakes to > 3.2 for QDs), raising the minimum energy of its conduction band (from -4.3 eV for the flakes to -2.2 eV for QDs) above the one of conduction band of MAPbI3 (between -3.7 and -4 eV) and hindering electron collection. The van der Waals hybridization of MoS2 QDs with functionalized reduced graphene oxide (f-RGO), obtained by chemical silanization-induced linkage between RGO and (3-mercaptopropyl)trimethoxysilane, is effective to homogenize the deposition of HTLs or ABLs onto the perovskite film, since the two-dimensional (2D) nature of RGO effectively plug the pinholes of the MoS2 QDs films. Our "graphene interface engineering" (GIE) strategy based on van der Waals MoS2 QD/graphene hybrids enable MAPbI3-based PSCs to achieve PCE up to 20.12% (average PCE of 18.8%). The possibility to combine quantum and chemical effects into GIE, coupled with the recent success of graphene and GRMs as interfacial layer, represents a promising approach for the development of next-generation PSCs. Figure 1. (a) Sketch of mesoscopic MAPbI3-based PSC exploiting MoS2 QDs:f-RGO hybrids as both HTL and ABL. (b) Scheme of the energy band edge positions of the materials used in the different components of the assembled mesoscopic MAPbI3-based PSC. The energy band edge positions of MoS2 flakes and MoS2 QDs were determined from OAS and UPS measurements detailed along the text, while those of the other materials were taken from literature: FTO, 52 TiO2, 52 MAPbI3, 134-139 spiro-OMeTAD 52 and Au 52 . (c) State-of-the-art and predicted PCE evolution for PSCs, highlighting the synergistic potential of GIE and the formulation of advanced perovskite chemistries. The RGO flakes are effective to plug the pinholes MoS2 QDs films, thus to homogenize the HTL. The choice of the functionalization for RGO relies on the bifunctional r...

Tin-halide perovskites have great potential as photovoltaic materials, but their performance is hampered by undesirable oxidation of Sn(II) to Sn(IV). In this work, we use nuclear magnetic resonance spectroscopy (NMR)...

Tin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.

Tin is one of the most promising alternatives to lead to make lead-free halide perovskites for optoelectronics. However, the stability of tin-based perovskites is hindered by the oxidation of Sn­(II) to Sn­(IV). Recent works established that dimethyl sulfoxide, which is one of the best-performing solvents for processing perovskite, is the primary source of tin oxidation. The quest for a stable solvent could be a game-changer in the stability of tin-based perovskites. Starting from a database of over 2000 solvents, we identified a series of 12 new solvents suitable for the processing of formamidinium tin iodide perovskite (FASnI3) by investigating (1) the solubility of the precursor chemicals FAI and SnI2, (2) the thermal stability of the precursor solution, and (3) the possibility of forming perovskite. Finally, we demonstrate a new solvent system to produce solar cells outperforming those based on DMSO. Our work provides guidelines for further identification of new solvents or solvent mixtures for preparing stable tin-based perovskites.

All inorganic perovskite solar cells lead to extended device lifespan in an accelerated ageing test.

The power conversion efficiency (PCE) of NiO based perovskite solar cells recently hit a record 22.1% with hybrid organic-inorganic perovskite composition and a PCE above 15% in the full inorganic...

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.