Large-Area Exfoliated Lead-Free Perovskite-Derivative Single-Crystalline Membrane for Flexible Low-Defect Photodetectors

Wide applications of personal consumer electronics have tended to cause a huge demand for smart and portable electronics, featuring mechanical flexibility, lightweight, and environmental friendliness. However, most of the recently reported flexible photodetectors based on micro-crystalline and amorphous components commonly suffer from severe drawbacks, including plenty of grains, boundaries, and surface defects. Here, we present a new lead-free chiral perovskite-derivative light absorber of (aminoguanidinium)(3)Bi2I9 (AG(3)Bi(2)I(9)), which displays a narrow direct band gap of about 1.89 eV. High-quality bulk single crystals were successfully grown with dimensions up to 24 x 12 x 5 mm(3). Emphatically, as-grown bulk single crystals are easy to be exfoliated for large-area ultrathin wafers with an exfoliated area up to 0.6 cm(2), showing promise for low-defect flexible optoelectronic applications. The remarkable surface smoothness and crystalline quality of single-crystalline thin layers were further confirmed by TEM, HRTEM, AFM, single-crystalline X-ray diffraction, and space-charge limited current (SCLC) measurements. As expected, the planar photodetectors based on flexible exfoliated wafers are first fabricated and exhibit notable photoelectric performance. This work represents an important step forward as it offers an effective strategy for the fabrication of high-quality large-area flexible exfoliated wafer devices.