Photodiode Response in a CH₃NH₃PbI₃/CH₃NH₃SnI₃ Heterojunction

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Since the discovery of its photovoltaic properties organometallic salt CH₃NH₃PbI₃ became the subject of vivid interest. The material exhibits high light conversion efficiency, it lases in red color, and it can serve as the basis for light emitting diodes and photodetectors. Here we report another surprising feature of this material family, the photo-tunability of the diode response of a heterojunction made of CH₃NH₃PbI₃ and its close relative, CH₃NH₃SnI₃. 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 opto-electronic devices.