Healing defects with triiodide ions: Deep-level defects in organic-inorganic perovskites decrease the performance of solar cells through unproductive recombination of charge carriers. Yang et al. show that introducing additional triiodide ions during the formation of layers of formamidinium lead iodide, which also contain small amounts of methylammonium lead bromide, suppresses the formation of deep-level defects. This process boosts the certified efficiency of 1-cm ² solar cells to almost 20%. Science , this issue p. 1376

We fabricated multi-layered graphene/MoS₂heterostructured devices by positioning mechanically exfoliated bulk graphite and single-crystalline 2H-MoS₂onto Au metal pads on a SiO₂/Si substrateviaa contamination-free dry transfer technique. We also studied the electrical transport properties of Au/MoS₂junction devices for systematic comparison. A previous work has demonstrated the existence of a positive Schottky barrier height (SBH) in the metal/MoS₂system. However, analysis of the SBH indicates that the contacts of the multi-layered graphene/MoS₂have tunable negative barriers in the range of 300 to −46 meV as a function of gate voltage. It is hypothesized that this tunable SBH is responsible for the modulation of the work function of the thick graphene in these devices. Despite the large number of graphene layers, it is possible to form ohmic contacts, which will provide new opportunities for the engineering of highly efficient contacts in flexible electronics and photonics.

Two-dimensional (2D) crystals have a multitude of forms, including semi-metals, semiconductors, and insulators, which are ideal for assembling isolated 2D atomic materials to create van der Waals (vdW) heterostructures. Recently, artificially-stacked materials have been considered promising candidates for nanoelectronic and optoelectronic applications. In this study, we report the vertical integration of layered structures for the fabrication of prototype non-volatile memory devices. A semiconducting-tungsten-disulfide-channel-based memory device is created by sandwiching high-density-of-states multi-layered graphene as a carrier-confining layer between tunnel barriers of hexagonal boron nitride (hBN) and silicon dioxide. The results reveal that a memory window of up to 20 V is opened, leading to a high current ratio (>10³) between programming and erasing states. The proposed design combination produced layered materials that allow devices to attain perfect retention at 13% charge loss after 10 years, offering new possibilities for the integration of transparent, flexible electronic systems.

We demonstrated p-type conduction in MoS₂ grown with phosphorous pentoxide via chemical vapor deposition (CVD). Monolayer MoS₂ with a triangular shape and 15-µm grains was confirmed by atomic force microscopy. The difference between the Raman signals of the A_1g and E¹_2g modes for both the pristine and P-doped samples was 19.4 cm⁻¹. In the X-ray photoelectron spectroscopy results, the main core level peaks of P-doped MoS₂ downshifted by about 0.5 eV to a lower binding energy compared to the pristine material. Field-effect transistors (FETs) fabricated with the P-doped monolayer MoS₂ showed p-type conduction with a field-effect mobility of 0.023 cm²/V⋅s and an on/off current ratio of 10³, while FETs with the pristine MoS₂ showed n-type behavior with a field-effect mobility of 29.7 cm²/V⋅s and an on/off current ratio of 10⁵. The carriers in the FET channel were identified as holes with a concentration of 1.01 × 10¹¹ cm⁻² in P-doped MoS₂, while the pristine material had an electron concentration of 6.47 × 10¹¹ cm⁻².