CH3NH3PbI3-based solar cells were characterized with electron beam-induced current (EBIC) and compared to CH3NH3PbI(3-x)Clx ones. A spatial map of charge separation efficiency in working cells shows p-i-n structures for both thin film cells. Effective diffusion lengths, LD, (from EBIC profile) show that holes are extracted significantly more efficiently than electrons in CH3NH3PbI3, explaining why CH3NH3PbI3-based cells require mesoporous electron conductors, while CH3NH3PbI(3-Clx ones, where LD values are comparable for both charge types, do not.

Wet chemical screening reveals the very high reactivity of Mo(NMe ) with H S for the low-temperature synthesis of MoS . This observation motivated an investigation of Mo(NMe ) as a volatile precursor for the atomic layer deposition (ALD) of MoS thin films. Herein we report that Mo(NMe ) enables MoS film growth at record low temperatures-as low as 60 °C. The as-deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforward fabrication of diverse device structures.

We h a ve applied a simultaneous combination of scanning Kelvin probe microscopy and scanning atomic force microscopy to the problem of pro ling dopant concentrations in two dimensions in silicon microstructures. By measuring the electrochemical potential di erence which minimizes the electrostatic force between probe tip and sample surface, we estimate the work function di erence between the tip and surface. To the extent that this work function di erence is a consequence of the dopant concentration at, or near, the sample surface, we infer doping pro les from our measurement. Structures examined and presented here include contact holes, and the technologically signi cant lightly-doped drain of a metal-oxide-silicon eld-e ect transistor. Using this methodology, w e are able to distinguish relative c hanges in dopant concentration with lateral resolution less than 100 nm. Sample preparation is minimal, and measurement time is fast compared to other techniques. Our measurements have been compared to predictions based on two-and three-dimensional process and device simulation tools. The comparisons show our technique is sensitive t o c hanges in dopant concentration, from 10 15 cm ,3 to 10 20 cm ,3 , of less than ten percent at these size scales. Suggestions to resolve absolute dopant concentration are made.

Cross-sections of a hole-conductor-free CH3NH3PbI3 perovskite solar cell were characterized with Kelvin probe force microscopy. A depletion region width of about 45 nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells.

A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of anti-ambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated anti-ambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. 2For example, the versatility of this scheme is demonstrated via contact-doped MoS2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with subdiffraction channel lengths in the range of 150 nm to 800 nm using photolithography on large-area MoS2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step towards the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems. TOC IMAGE 3Parallel self-aligned fabrication methods in modern silicon-based microelectronics have enabled sub-lithographic registration between processing steps, ultimately facilitating substantial advances in circuit complexity over the past few decades. 1 In contrast, while two-dimensional (2D) materials have shown significant potential for digital and analog electronics due to their high mobilities, ultrathin geometry, and broad range of permutations in van der Waals heterojunctions (vdWHs), 2-9 2D material devices have not yet exploited parallel self-aligned fabrication to achieve both short channels and large area fabrication. Thus far, short-channel 2D material transistors and vdWHs have been achieved using serial processing methods such as electron-beam lithography or mechanical placement on nanotube or nanowire gates. 5,10,11 Similarly, the relative alignment of different layers in vdWHs has been inhibited by the diffraction-limited resolution of transfer and alignment methods. Here, we overcome these limitations by introducing a self-aligned processing methodology that enables the fabrication of 2D material transistors with channel lengths below 150 nm with minimal short-channel effects and improved current saturation, as demonstrated with monolayer MoS2. These self-aligned transistors show the highest output resistance at the lowest channel length reported for a 2D material, which is of interest for high-frequency current amplifiers and mixers. In vdWHs based on black phosphorus (BP) and MoS2, this self-aligned approach allows dual-gate ...