Tebyetekerwa, MikeZhang, Jian (Andrew)Liang, KunDuong, TheNeupane, GuruZhang, LinglongLiu, BoqingTruong, ThienBasnet, RabinQiao, XiaojingYin, ZongyouLu, YueruiMacdonald, DanielNguyen, Hieu2020-09-160935-9648http://hdl.handle.net/1885/210517One of the most fundamental parameters of any photovoltaic material is its quasi‐Fermi level splitting (∆µ) under illumination. This quantity represents the maximum open‐circuit voltage (Voc) that a solar cell fabricated from that material can achieve. Herein, a contactless, nondestructive method to quantify this parameter for atomically thin 2D transition metal dichalcogenides (TMDs) is reported. The technique is applied to quantify the upper limits of Voc that can possibly be achieved from monolayer WS2, MoS2, WSe2, and MoSe2‐based solar cells, and they are compared with state‐of‐the‐art perovskites. These results show that Voc values of ≈1.4, ≈1.12, ≈1.06, and ≈0.93 V can be potentially achieved from solar cells fabricated from WS2, MoS2, WSe2, and MoSe2 monolayers at 1 Sun illumination, respectively. It is also observed that ∆µ is inhomogeneous across different regions of these monolayers. Moreover, it is attempted to engineer the observed ∆µ heterogeneity by electrically gating the TMD monolayers in a metal‐oxide‐semiconductor structure that effectively changes the doping level of the monolayers electrostatically and improves their ∆µ heterogeneity. The values of ∆µ determined from this work reveal the potential of atomically thin TMDs for high‐voltage, ultralight, flexible, and eye‐transparent future solar cells.This work was supported by the Australian Renewable Energy Agency (ARENA) through Research Grant RND017. The authors acknowledge the facilities and technical support from the Australian National Fabrication Facility (ANFF), ACT Node, and the Australian Microscopy & Microanalysis Research Facility at the Centre of Advanced Microscopy and at the Australian National University. M.T. acknowledges the research support of the Australian Government Research Training Program (RTP) Scholarship. H.T.N. acknowledges the fellowship support from the Australian Centre for Advanced Photovoltaics (ACAP). K.L. and X.J.Q. acknowledge the support from the International Graduate Exchange Program of the Beijing Institute of Technology.application/pdfen-AU© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim201910.1002/adma.2019005222020-06-23