Photovoltaic devices based on lead iodide perovskite films have seen rapid advancements, recently achieving an impressive 17.9% certified solar power conversion efficiency. Reports have consistently emphasized that the specific choice of growth conditions and chemical precursors is central to achieving superior performance from these materials; yet the roles and mechanisms underlying the selection of materials processing route is poorly understood. Here we show that films grown under iodine-rich conditions are prone to a high density of deep electronic traps (recombination centers), while the use of a chloride precursor avoids the formation of key defects (Pb atom substituted by I) responsible for short diffusion lengths and poor photovoltaic performance. Furthermore, the lowest-energy surfaces of perovskite crystals are found to be entirely trap-free, preserving both electron and hole delocalization to a remarkable degree, helping to account for explaining the success of polycrystalline perovskite films. We construct perovskite films from I-poor conditions using a lead acetate precursor, and our measurement of a long (600 ± 40 nm) diffusion length confirms this new picture of the importance of growth conditions.

X-ray tomography has emerged as a powerful technique for studying lithium ion batteries, allowing nondestructive and often quantitative imaging of these complex systems, which contain solid components with length scales spanning orders of magnitude and which are in-filled with liquid electrolyte. Over the past decade, X-ray tomography has allowed interrogation of structure and material composition, providing quantitative or qualitative insight into battery operation and degradation. In this review, we first provide an overview of X-ray tomography and explore what types of experiments can yield insight into open questions in the lithium ion battery research field. In the second half of the review, we discuss the aspects a researcher must consider, and we summarize challenges and approaches to sample preparation, experimental setup, and data analysis. Finally, we describe both outstanding challenges and promise in using X-ray tomography for lithium ion battery research.

Capacity fade in lithium-ion battery electrodes can result from a degradation mechanism in which the carbon black-binder network detaches from the active material. Here we present two approaches to visualize and quantify this detachment and use the experimental results to develop and validate a model that considers how the active particle size, the viscoelastic parameters of the composite electrode, the adhesion between the active particle and the carbon black-binder domain, and the solid electrolyte interphase growth rate impact detachment and capacity fade. Using carbon-silicon composite electrodes as a model system, we demonstrate X-ray nano-tomography and backscatter scanning electron microscopy with sufficient resolution and contrast to segment the pore space, active particles, and carbon black-binder domain and quantify delamination as a function of cycle number. The validated model is further used to discuss how detachment and capacity fade in high-capacity materials can be minimized through materials engineering.

Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of magnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

We present transport measurements performed in InAs/GaSb double quantum wells. At the electron-hole crossover tuned by a gate voltage, a strong increase in the longitudinal resistivity is observed with increasing perpendicular magnetic field. Concomitantly with a local resistance exceeding the resistance quantum by an order of magnitude, we find a pronounced non-local resistance signal of almost similar magnitude. The co-existence of these two effects is reconciled in a model of counter-propagating and dissipative quantum Hall edge channels providing backscattering, shorted by a residual bulk conductivity.An InAs/GaSb double quantum well (QW) sandwiched between two AlSb barriers shows a peculiar band alignment [1]. A QW for electrons in InAs and a QW for holes in GaSb coexist next to each other. If the QWs thicknesses are small enough, a hybridization gap is expected to open at the charge neutrality point (CNP) [2,3]. Depending on the QWs' thicknesses and on the perpendicular electric field, a rich phase diagram is predicted [4]. It should be possible to electrically tune the sample from standard conducting phases to insulating, semimetallic or topological insulator phases. Recent work on InAs/GaSb QWs showed signatures of topological phases in micron-sized Hall bars at zero magnetic field [5][6][7], as expected for the quantum spin Hall insulator regime [8]. Beyond the topological insulator properties, that manifest themselves, the fate of topological edge states at finite magnetic field has not been investigated so far. Similarly to other semi-metals like graphene [9,10] or CdHgTe/HgTe quantum wells [11,12], electron and hole Landau levels (LLs) can coexist close to the CNP [13,14]. A detailed understanding of the expected hybridization of LLs [15] and its manifestation in a transport experiment is still missing.Here we present magnetotransport measurements performed on gated InAs/GaSb double QWs. At high magnetic fields, in the electron and hole regimes, we observe the formation of standard LLs. Close to the CNP a peculiar state forms in which electrical transport is governed by counter-propagating edge channels of highly dissipative nature. We investigate the transport properties in this regime using different measurement configurations, and as a function of magnetic field and temperature.The experiments were performed on two devices (named device A and device B) obtained from the same wafer as described in Ref. 16. In Ref. 17 a nominally identical structure was used, and a hybridization gap of 3.6 meV was reported. Hall bar structures were fabricated by photolithography and argon plasma etching. Device A consisted of a single Hall bar with a width of 25 µm and a separation between lateral arms of 50 µm.Device B consisted of two Hall bars in series, oriented perpendicularly to each other. Their width is 25 µm and the lateral voltage probes have various separations, the shortest being 50 µm . Device A was covered by a 200 nm thick Si 3 N 4 insulating layer, device B by a 40 nm thick HfO 2 layer. On both sampl...