Oriented Growth of Ultrathin Single Crystals of 2D Ruddlesden–Popper Hybrid Lead Iodide Perovskites for High-Performance Photodetectors

Compared with their 3D counterparts, layered 2D Ruddlesden–Popper perovskites (2D RPPs) with the formula of (A′)2An–1PbnX3n+1 exhibit improved photo and moisture stability. To develop flexible single-crystalline electronics and wearable devices, cost-effective growth of large-area single crystals of 2D RPPs with large lateral size, ultrathin thickness, parallel orientation, and well-defined and controlled n values are highly desirable, but it remains still a challenge. Here, we modified the space-confined aqueous solution growth method to fabricate single-crystalline films of (BA)2(MA)n？1PbnX3n+1 and n = 1, 2, 3, respectively, with the lateral size reaching millimeter and thickness about 400–1000 nm. Moreover, the quantum well layers are found to be parallel to the substrate, well suitable for lateral transport requirement. We successfully integrated ultrathin single crystals of (BA)2(MA)n？1PbnX3n+1 (n = 1–3) into a metal–semiconductor–metal two-terminal photodetector. The photoresponsive wavelength range was extended from 525 nm for n = 1 and 590 nm for n = 2 to 630 nm for n = 3 as a result of the reduced exciton band gap. The device of n = 2 single crystals shows the highest responsivity of 2.96 A/W and a detectivity of 1013 jones, while the device of n = 3 shows the lowest dark current 10–14 A, and therefore, its on/off ratio reaches 2862 at the bias voltage of 1 V