Photodiode Response in a CH 3 NH 3 PbI 3 /CH 3 NH 3 SnI 3 Heterojunction.

Here we report another surprising feature of the methylammonium metal halide material family, the phototunability of the diode response of a heterojunction made of CH3 NH3 PbI3 and its close relative, CH3 NH3 SnI3 . In the dark state the device behaves as a diode, with the Sn homologue acting as the "p" side. The junction is extremely sensitive to illumination. A complete reversal of the diode polarity, the first observation of its kind, is seen when the junction is exposed to red laser light of 25 mW/cm2 or larger power density. This finding opens up the possibility for a novel class of optoelectronic devices.