Vertically Oriented Single‐Layer Grains for a Highly Bifunctional Perovskite Photovoltaic Light‐Emitting Device

ABSTRACT The realization of bifunctional perovskite devices integrating photovoltaic (PV) and light‐emitting diode (LED) capabilities requires precisely controlled grain architectures to facilitate dual carrier transport pathways. In this work, sulfaguanidine (SG) molecules were introduced into the perovskite solution to reconstruct the crystallization kinetics and further form vertically oriented single‐layer grains in FAPbI 3 films. The guanidinium group (−NH‐C (=NH)‐NH 2 ‐) and the sulfonamide group (−SO 2 ‐NH‐) synergistically create continuous carrier channels: The former bridges adjacent grains through Pb 2+ coordination, whereas the latter establishes hydrogen‐bonding networks with FA + cations. This through‐thickness transport structure simultaneously enhances out‐of‐plane charge transport and enables bidirectional functionality, resulting in an increase of approximately one order of magnitude in the carrier mobility. Consequently, the external quantum efficiency (EQE) of the device increased from 14.4% to 25.8%, with a record‐ultralow turn‐on voltage of 1.10 V and < 20% EQE roll‐off at a current of 500 mA cm −2 , while maintaining 12.58% PV efficiency. This work establishes through‐thickness transport structure engineering as a critical strategy for developing monolithic optoelectronic systems.