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')2A n-1Pb nX3 n+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-1Pb nX3 n+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-1Pb nX3 n+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.