Metal halide perovskites are emerging as promising semiconductors for cost-effective and high-performance optoelectronic devices. Tremendous research attention has been attracted to perovskite layers, however, an in-depth understanding of how the buried charge transport layers affect the perovskite crystallization, compositions and film quality, though of critical importance, is currently unclear.

Here, we firstly, systematically studied synergy effects between perovskite precursor stoichiometry and interfacial reactions for high-performance perovskite LEDs (PeLEDs) and establish useful guidelines for rational device optimization. We reveal that efficient deprotonation of the undesirable organic cations by a metal oxide interlayer with a high isoelectric point is critical to promote the transition of intermediate phases to highly emissive perovskite films.^[1] We further reveal that the deprotonation of FA+ cations and the formation of hydrogen-bonded gels consisting of CsI and FA facilitated by zinc oxide underneath, effectively removes the Cs-FA ion-exchange barrier, promoting the formation of phase-pure CsxFA1-xPbI3 films with emission filling the gap between that of pure Cs- and FA-based perovskites.Based on this discovery, we successfully fabricated a set of highly emissive Cs_xFA_1-xPbI₃ perovskite films with fine-tuning Cs-FA alloying ratio for emission-tuneable near-infrared light-emitting diodes (NIR-LEDs).^[2]

We further developed a multifunctional display using highly photo-responsive metal halide PeLEDs as pixels following works mentioned above. by careful control of the interfacial reactions, we achieved  strong photo response of the PeLED pixels. Therefore, the display can be simultaneously used as touch screen, fingerprint sensor, ambient light sensor, and image sensor without integrating any additional sensors. In addition, decent light-to-electricity conversion efficiency of the pixels also enables the display to act as a photovoltaic device to charge the equipment.^[3] The multiple-functions of our PeLED pixels can not only simplify the display module structure and realize ultra-thin and light-weight display, but also significantly enhance the user experience by these advanced new applications. As such, our results demonstrate great potential of PeLEDs for a new generation of displays for future electronic devices.