Photoconducting Devices with Specific Attributes based on 2D Metal-Halide Perovskites

Flexible optoelectronic devices offer possibilities for a wide range of novel applications. Especially flexible photodetectors enable functionalities like optical communication or optical sensing for healthcare, lifestyle applications or optical cross-linking systems in the “Internet of Things”. These diverse applications areas result in a variety of required device attributes. One device architecture which is noncomplex, easy-to-fabricate and allows facile tuning of the device functionalities are photoconducting devices. Herein the conductivity of a semiconducting channel is mediated through illumination. By engineering the optical properties as well as the structure of the semiconductor, the functionality of the photodetectors can be altered to meet requirements for specific applications, e.g., defined color ranges, high sensitivities or low noise signals. <br/>Promising materials for flexible photoconducting devices are two dimensional (2D) metal-halide perovskites, which can be fabricated at room temperature out of solution and crystalize as naturally grown multi quantum wells in the form of inorganic semiconducting layers separated by bilayers of electrically insulating organic cations. 2D perovskites exhibit mechanical flexibility combined with the optical and electronic properties of a 2D system.<br/>Here we show, that the excitonic absorption feature of 2D perovskite (BA)₂PbI₄ can be utilized to realize filter-free narrow-bandgap photodetectors. We report the fabrication of a lateral, wavelength selective photodetector based on n=1 (BA)₂PbI₄, exhibiting a well defined peak in the photocurrent spectrum at 520 nm, which can be related to the excitonic absorption. We achieve colour-selective light detection with a responsivity of 0.750 mA/W and a specific detectivity up to 4.7x10¹⁰ J. On-Off ratios are larger than 10⁴.<br/>Aiming for high-responsive device, we combine a non-continued layer of (BA)₂PbI₄ 2D perovskite with a transition metal dichalcogenide as conducting channel to achieve a 2D/2D hetero-photodetector with a gain mechanism. In this architecture, the two-dimensional (BA)₂PbI₄ layer traps the minority charge carriers (holes), enabling the electrons to circulate through the transition metal dichalcogenide channel multiple times. Using optimized channel length, we achieve responsivities of up to 20 A/W, which corresponds to a gain of 38.