The deposition of a thin C60 (acceptor) layer in vacuum on CH3NH3PbI3 perovskite (donor) creates a hybrid PHJ to yield the photovoltaic effect. The C60 molecule layer has a dual function, where first, it forms a heterojunction with the perovskite for efficient charge separation, and second, it effectively collects the electrons. Our results confirm the CH3NH3PbI3 perovskite/C60 or C60 derivatives PHJ being developed as a newly-structured, hybrid, efficient solar cells. This was a breakthrough in perovskite solar cell research and subsequently opened up new directions for the formation of p-i-n heterojunctions to perovskite solar cells. In other words, we can use the knowledge and novel interfacial techniques been developed from the studies of organic photovoltaics to advance the performance of perovskite solar cells. Even up to today, the record efficiency perovskite solar cells still adopt the idea of a heterojunction in the device structure.

The alignment of energy level minimizes the interfacial energy losses for the transport of holes. In addition, NiOxsuppresses the carrier recombination at the electrode thereby optimizing the photovoltage output of device. Since there are many n-type metal oxide materials (TiO2, ZnO, SnO2) available for perovskite-based solar cells, in future perovskite solar cells can be made of both inorganic p-type and n-type metal oxide as the electrode interlayers (p-type metal oxide/perovskite/n-type metal oxide).

We are aware that the quality of the perovskite active layer would still be a key component to advance the development of perovskite-based hybrid LEDs and could be further improved by the delicate control on the equilibrium condition between a liquid-phase CH3NH3PbBr3•xMA intermediate with solid-phase CH3NH3PbBr3. The hybrid perovskite-based LED reported in this work exhibits a magnitude of electroluminescence higher than 70,000 cd/m2 and a peak luminous efficiency of 16.0 cd/A. The brightness of our result significantly outperformed the state-of-the-art value at that time. Such a high brightness implies that the device configuration and the quality of our treated perovskite film can sustain high injection of carriers without device failure, posing a feasible gas-solid process to largely improve the performance and the design of the highly bright and efficient perovskite-based LEDs for real applications.The merits of the methods we developed in the reported paper represents a new paradigm for hybrid perovskite-based LED with a conventional OLED architecture. We report that the commonly used PEDOT:PSS hole transport layer needs to be substituted by a more suitable electrode interlayer, such as a compact nickel oxide (NiOx) layer herein. More importantly, we have developed a process to moderately generate methylamine (MA) gas to treat CH3NH3PbBr3 film in a relatively slow reaction way through the unique gas-solid reaction. MA treatment promotes the re-growth of CH3NH3PbBr3 crystallites on NiOx layer following the preferred orientations and significantly enhances the film qualities. The Top figure illustrates the device configuration of CH3NH3PbBr3-based perovskite LED and the scheme of MA treatment for CH3NH3PbBr3 perovskite film.

This was the work to develop a low-pressure vapor-assisted solution process in preparing 2D, hybrid 2D/3D, and 3D polycrystalline perovskite thin film. Under the low-pressure chemical vapor reaction, we verified that the coexistence of low-dimensional perovskite modulated the growth of polycrystalline perovskite film as well as passivated the boundary interfaces. The proposed mechanisms were of the great importance to regulate the parameters to fine tune the growth of polycrystalline perovskite crystals through the vapor-assisted reaction, which is a suitable approach to prepare the large area perovskite thin film for real applications.

The external electric bias in operating CH3NH3PbBr3 perovskite LEDs drives the migration of mobile ions and causes the bias-induced enhancement of luminance. We pointed out that the high magnitude of luminance and efficiency at the high current density regime in perovskite LEDs possibly are the results regulated by the external electric bias, which cannot truly assess the output performance of the device in nature. Adding the zwitterion molecule, Choline chloride (Ch.Cl), in CH3NH3PbBr3precursor solution for preparing polycrystalline perovskite film effectively interferes the migration of ions crossing the grains in perovskite LEDs as verified by the higher calculated magnitude of the activation energy for the migration of mobile ions.