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 microcrystalline 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)3Bi2I9 (AG3Bi2I9),
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 × 12 × 5 mm3. Emphatically, as-grown bulk
single crystals are easy to be exfoliated for large-area ultrathin
wafers with an exfoliated area up to 0.6 cm2, 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.