Fusible Low Work Function Top Electrode for Vacuum-Free Perovskite Light-Emitting Diode Application: Role of OH-Terminated Sn Atoms at the Alloy Surface

Hybrid organic–inorganic halide perovskite-based light-emitting diodes (PeLEDs) have attracted tremendous interest because of their higher external quantum efficiency and low production cost. Most of the high efficiency PeLEDs utilize a p–i–n structure geometry, which require a sufficiently low work function top metal electrodes for better charge injection. Also, PeLEDs can be fabricated at low temperature except the top metal electrodes. In conventional PeLEDs, metal electrodes are deposited by thermal deposition, which greatly reduces the production yield and enhances the complexity and production cost. Here, we have demonstrated a facile low-temperature and vacuum-free deposition method for conformal coating of the low melting point alloy as the top cathode electrode which also facilitates efficient charge extraction. Ultraviolet photoelectron spectroscopy measurement has been performed to estimate the work function of this low melting point alloy. To our surprise, a sufficiently low work function (∼3.01 eV) has been observed despite all the constituents having a work function around 4.0 eV. XPS measurement confirms the presence of a metal hydroxide at the electrode interface which is responsible for achieving such a low work function due to surface polarization. These devices are relatively more stable compared to other low work function metal electrode-based PeLEDs.