Monolayer, few‐layer, and thin‐film MoS2 is synthesized using chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. The complex refractive index of these samples is assessed using variable angle spectroscopic ellipsometry (VASE) measurements over a broad spectral range between 190 and 1700 nm. The ellipsometry data are sensitive to birefringence effects in the thickest thin‐film sample. These birefringence effects are investigated, and an analysis method is developed to extract the in‐plane and out‐of‐plane optical properties. The complex refractive index is then used to calculate reflectance, transmittance, and absorption of the MoS2 films using the transfer‐matrix method (TMM) and is matched with experimentally measured transmittance of the same samples. The modeled results show that the monolayer, few‐layer, and thin‐film MoS2 absorbs 7.4%, 12.6%, and 32.4% of the incident light, respectively, between 300 and 700 nm. When normalized to per unit‐thickness absorption, they absorb 12.1%, 5.9%, and 1.1% nm−1, respectively, clearly showing superior light–matter interaction in the monolayer and few‐layer films. These new complex refractive index data are further used to design optical coatings for these films to either confine absorption in a narrow bandwidth for photodetector applications or enhance broadband absorption for photovoltaic applications.

The deployment of two-dimensional (2D) materials for solar energy conversion requires scalable large-area devices. Here, we present the design, modeling, fabrication, and characterization of monolayer MoS 2 -based lateral Schottky-junction photovoltaic (PV) devices grown by using chemical vapor deposition (CVD). The device design consists of asymmetric Ti and Pt metal contacts with a work function offset to enable charge separation. These early stage devices show repeatable performance under 1 sun illumination, with V OC of 160 mV, J SC of 0.01 mA/cm 2 , power conversion efficiency of 0.0005%, and specific power of 1.58 kW/kg. An optoelectronic model for this device is developed and validated with experimental results. This model is used to understand loss mechanisms and project optimized device designs. The model predicts that a 2D PV device with ∼70 kW/kg of specific power can be achieved with minimum optimization to the current devices. By increasing the thickness of the absorber layer, we can achieve even higher performance devices. Finally, a 25 mm 2 area solar cell made with a 0.65 nm thick MoS 2 monolayer is demonstrated, showing V OC of 210 mV under 1 sun illumination. This is the first demonstration of a large-area PV device made with CVD-grown scalable 2D materials.

Two-dimensional semiconductors, such as MoS2, are leading candidates for the production of next-generation optoelectronic devices such as ultrathin photodetectors and photovoltaics. However, the commercial application of 2D semiconductors is hindered by growth techniques requiring hours of heating and cooling cycles to produce large-area 2D materials. We present here a growth technique that leverages high-intensity optical irradiation of a solution-processed (NH4)2MoS4 precursor to synthesize MoS2 in one-tenth the time of typical furnace-based CVD. From start to finish, the technique produces uniform 2D MoS2 across 4-in. wafers within 15 min. Raman spectroscopy, in-plane XRD, and XPS show a 2H MoS2 crystal structure with a stoichiometry of 1.8:1 S:Mo. AFM scans show that the films are 2.0 nm thick MoS2 with a roughness of 0.68 nm. Photoluminescence spectroscopy reveals the characteristic 1.85 eV bandgap. The as-grown films were used to make field-effect transistors with a mobility of 0.022 cm2 V−1 s−1 and photodetectors with a responsivity of 300 mA/W and an external quantum efficiency of 0.016%, demonstrating their potential for optoelectronic device development. This rapid thermal processing growth technique reduces MoS2 synthesis time by an order of magnitude relative to comparable techniques and enables greater accessibility to 2D semiconductors for researchers and developers.

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