Metal halide perovskites have been used in various optoelectronic applications, such as solar cells, lasers and photodetectors. The material class is of particular interest for the photodetector field since the band gap varies with its composition. Using tin-based hybrid inorganic-organic perovskites leads to near-infrared sensitive photodetectors . By changing the composition of lead-based perovskites one can achieve band gaps varying over the visible spectrum from 550 to 800 nm [2, 3]. With copper as the metal cation it is possible to synthesize materials with even higher band gaps . The fact that all of these perovskites can easily be made in single crystal form makes them even more attractive for photodetector applications since they are typically more stable and have lower trap densities than their thin film counterparts. Especially the two-dimensional perovskites are known for their superior stability against humidity compared to the 3D compounds .
Here we report the performance of photodetectors made of various 2D perovskite single crystals and compare these to their 3D counterparts. Among the 2D materials investigated are phenylethylamine lead iodide ((PEA)2PbI4) and copper-based perovskites as MA2CuCl4. They are used in the lateral type photoconductor layout, in which two metal electrodes are deposited on the same side of the perovskite crystal. This typically has the advantage of high photocurrent and high responsivity, at the expense of relatively slow response times .
We demonstrated in our earlier work that perovskite single crystals made of methylammonium lead bromide can be used as a gas detector . This effect is governed by the surface trap state density and its modulation by physisorption of gases, and it is evident from a change in photocurrent upon light exposure. Previously we focused on the effects of nitrogen, carbon dioxide, argon, oxygen, air and water on the MAPbBr3 crystal’s optoelectronic properties. Here we expand this to the two-dimensional perovskite photoconductors mentioned above. In addition, we characterize the behavior of these devices under additional gases such as alcohols and ketones, which might play a role in lung cancer detection.
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