: Changhyun Han, Hyunho Jung, Jongho Lee, Myungjae Lee, Yeonsang Park, Kyung-Sang Cho, and Heonsu Jeon

: Adv. Mater. Technol. 3(3) 1700291 (2018)

A method of wet-transferring a densely packed colloidal quantum dot (CQD) film is reported herein. Layers of poly(vinyl alcohol) (sacrificial layer) and poly(methyl methacrylate) (temporary mechanical support) are spin-coated below and above the CQD film, respectively; the two layers are eventually removed, resulting in a single CQD film on an alien substrate. CQD films as large as 1 cm  1 cm are transferred to any substrate, including flexible and prepatterned ones, with very little mechanical or optical damage. The wet-transfer method can be repeated to form a CQD heterostructure. A CQD distributed feedback (DFB) laser is also demonstrated by transferring a thick CdSe-based CQD layer (for both optical gain and waveguiding) on top of a surface grating structure. The resultant CQD structure exhibits a single-mode DFB lasing action, with a high spontaneous emission factor (  10-3 ), owing to a strong vertical mode confinement and smooth surface morphologies on both sides of the CQD waveguide layer.