In this work, we introduce a patterned organic layer in colloidal quantum-dot (CDQ) solar cells between the CQD solid and back metal electrode. This organic layer has preferred band alignment and suitable hole mobility, enabling it to act as an efficient hole-transport layer (HTL) instead of conventional 1,2-ethanedithiol (EDT)-treated CQD HTL.  In addition, this soft organic layer can be readily molded with soft nano-imprinting lithography and form high quality inverse 2D-photonic structure. The metal coated 2D photonic electrode generates such an efficient light scattering that we achieved a record External Quantum Efficiency (EQE) value of 86 % at 1220 nm.  This value is 20 % higher than previous best reports on IR PCE in CQD solar cells.

Nanostructured Back Reflectors for Efficient Colloidal Quantum-Dot Infrared Optoelectronics
Se-Woong Baek, Pau Molet, Min-Jae Choi, Margherita Biondi, Olivier Ouellette, James Fan, Sjoerd Hoogland, F. Pelayo García de Arquer, Agustín Mihi, Edward H. Sargent
Advanced Materials, 31 (33), 1901745, 2019
DOI: 10.1002/adma.201901745

Figure: a) Schematics of the PDMS imprinting process in CQD devices. b) Surface images and line profile of organic layer scanned by AFM after imprinting. Scale bar: 2 μm c) SEM images of organic hole transporting template after imprinting (left) and d) final metal structure deposited onto the organic template. e) Photograph of the pre-patterned PDMS mold (left) and the final IR CQD device after nano-imprinting (right).

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