Monolayer Molybdenum Disulfide Photovoltaics with Carrier Selective Contacts for High Open-Circuit Voltage

While the efficiencies of ultrathin transition metal dichalcogenide (TMDC)-based photovoltaics have shown significant progress due to their intrinsically strong light-matter interactions, little work has demonstrated that TMDC-based photovoltaics can achieve high photovoltaic performance with technologically useful active areas. In this work, we show that a vertical carrier selective contact architecture combined with gold-assisted exfoliation of TMDCs enables millimeter-area, monolayer molybdenum disulfide (MoS₂) photovoltaics. First, we show that under one-sun illumination, photovoltaic devices with a bulk TMDC active layer result in an open-circuit voltage of 523 mV; however, the non-radiative losses associated with the indirect bandgap in multilayer TMDCs limit the achievable open-circuit voltage. We designed a solar cell that leverages the high radiative efficiency of direct bandgap monolayer MoS₂, combined with the electron- and hole-transport layers, C₆₀ and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), respectively, to increase the achievable open-circuit voltage. To synthesize MoS₂on arbitrary substrates, we develop a photoresist transfer process that minimizes the impact of polymer residues on the device performance. Through Raman and photoluminescence measurements, we show comparable optoelectronic quality between gold-assisted and traditional direct tape exfoliated MoS₂ monolayers on silicon dioxide/silicon, which exhibit similar photoluminescence emission with peaks between 1.84 and 1.86 eV, with a linewidth of 0.13 eV, similar to results seen for MoS₂ monolayers directly exfoliated onto silicon dioxide. Raman measurements indicate a similar E¹_2g to A_1g frequency difference and peak linewidth of less than 8 cm^-1. Our methods and results demonstrate the possibility for high efficiency monolayer photovoltaics and opens the door to large-area scalability.