Light-Driven Permanent Charge Separation across a Hybrid Zero-Dimensional/Two-Dimensional Interface

Abstract

We report the first demonstration of light-driven permanent charge separation across an ultrathin solid-state zerodimensional (0D)/2D hybrid interface by coupling photoactive Sn-doped In 2 O 3 nanocrystals with monolayer MoS 2 , the latter serving as a hole collector. We demonstrate that the nanocrystals in this device-ready architecture act as local light-controlled charge sources by quasi-permanently donating ∼5 holes per nanocrystal to the monolayer MoS 2 . The amount of photoinduced contactless charge transfer to the monolayer MoS 2 competes with what is reached in electrostatically gated devices. Thus, we have constructed a hybrid bilayer structure in which the electrons and holes are separated into two different solid-state materials. The temporal evolution of the local doping levels of the monolayer MoS 2 follows a capacitive charging model with effective total capacitances in the femtofarad regime and areal capacitances in the μF cm −2 range. This analysis indicates that the 0D/2D hybrid system may be able to store light energy at densities of at least μJ cm −2 , presenting new potential foundational building blocks for next-generation nanodevices that can remotely control local charge density, power miniaturized circuitry, and harvest and store optical energy.

0D Nanocrystals as Light‐Driven, Localized Charge‐Injection Sources for the Contactless Manipulation of Atomically Thin 2D Materials

“…We find that the photo‐induced hole doping is quasi‐permanent, i.e., stable on a timescale of months as already reported in our previous work. [ 25 ] Notably, we observed comparable photo‐induced variations in similar systems in which we varied the position of the illumination spot on the flake (Figure S5, Supporting Information). No significant influence on the carrier‐density manipulation was found from the local injection point, but it rather corresponds to the initial level of n‐doping in the 2D material flake.…”

“…This reduction of trions results in an overall PL intensity increase, as the quantum yield of neutral exciton emission is higher than that for trions, thus increasing the overall PL efficiency of the 1L‐MoS 2 . [ 1,33 ] These changes in the emission spectrum, which do not occur for UV excitation of the 1L‐MoS 2 alone (Figure S1, Supporting Information), indicate that the UV excitation indeed results in the removal of free electrons from the 1L‐MoS 2 , likely through a photo‐induced p‐doping due to a hole transfer from the ITO NCs as sketched in Figure 1a,b and explained in detail by Kriegel et al [ 25 ]…”

“…[ 1,11,24,33 ] By applying the mass action model (see Supporting Information), which describes the equilibrium of excitons ( n x ), trions ( n x‐ ), and free carriers ( n e ) in the system, we calculate the initial electron carrier density of the flake (Figure 3c) and the final carrier density after the photodoping (Figure 3d). [ 25 ] From the comparison between the two carrier‐density maps, it is evident that the photodoping of the ITO NCs in the hybrid 1L‐MoS 2 /ITO system leads to a sharp reduction of the extra carriers in the 1L‐MoS 2 flake. Remarkably, the final concentration of charges in the semiconductor is more homogeneous than the initial one, with photodoping, leading to a smoother spatial distribution of the carrier density.…”

Photodoping of metal oxide nanocrystals for multi-charge accumulation and light-driven energy storage

“…As a first example, monolayer two-dimensional transition metal dichalcogenides (2D TMDs) were employed as all-solid-state hole-acceptors, accepting permanently multiple photo-generated holes from ITO NCs. 18 This work displays the successful charge separation and stable accumulation of multiple electrons and holes in separate units after photodoping, where the NC film represents the negative electrode, and the 2D TMD the positive one. The nanometer separation of the two separated plates when assuming a capacitor-like system composed of two plates of opposite charges highlights promising capacitance values of femto Farads (corresponding to areal capacitances of ∼μF cm −2 ).…”

“… 17 Recently, this solution-based photodoping process, has been transferred to an all-solid-state platform. 18 Despite these promising results, up to now in MO NCs only light-driven charge accumulation was demonstrated, while the fully-working device and the demonstration of light-driven energy storage remains an open task.…”