  Light emission and detection are the two fundamental attributes of
optoelectronic communication systems. Until now, both functions have been
demonstrated using the p-n diode which is exploited across a wide range of
applications. However, due to the competing dynamics of carrier injection and
photocarrier collection, with this device light emission and detection are
realized separately by switching the direction of the applied electrical bias.
Here we use mobile ions in halide perovskites to demonstrate light-emitting
photodetection in either condition of applied electrical bias. Our device
consists of a CsPbBr$_3$ microwire which is integrated with single-walled
carbon nanotube thin film electrodes. The dual functionality stems from the
modulation of an energetic barrier caused by the cooperative action of mobile
ions with the photogenerated charge carriers at the perovskite-electrode
interface. Furthermore, such complex charge dynamics also result in a novel
effect: light-enhanced electroluminescence. The observed new optoelectronic
phenomena in our simple lateral device design will expand the applications for
mixed ionic-electronic conductors in multifunctional optoelectronic devices .
