Solution-processed photodetector using high-purity semiconducting single-walled carbon nanotube/n-type polymer heterojunction

Abstract

Single-walled carbon nanotubes (SWNTs) are promising candidate as future photodetector applications due to their strong light absorption, high charge carrier mobility, band-gap controllability, solution processability, and flexibility. However, due to the high exciton binding energy and the presence of metallic SWNTs, the exciton dissociation and photo-induced carrier collection efficiency is compromised. A donor-acceptor type II heterojunction architecture is therefore often used to overcome these limitations. Previously, our group used fullerene (C60) as the electron acceptor and SWNTs as the electron donor. These devices, however, require sorting of semiconducting SWNTs from as synthesized SWNTs, removal of the surfactant, and subsequent deposition of fullerene, a relatively long multi-step process. Herein, we present a type II heterojunction photodetector where the active components are p-type semiconducting SWNT wrapped by an n-type conjugated polymer Tz-FT. The advantages of this hybrid material is that only one coating step is required and that the donor-acceptor interfacial area is maximized for efficient exciton dissociation and photo-induced carrier collection. When as-synthesized SWNTs are mixed with Tz-FT polymer in toluene and sonicated, the wrapped polymer-SWNT hybrid structure naturally forms. The metallic SWNTs are selectively eliminated as they sediment down during centrifugation. Solution of polymer-wrapped SWNT is shown in Results figure. Other figure shows Raman spectra of SWNT film, where it is evident that the metallic peaks (240 ~ 280 cm-1) are significantly reduced compared to as-synthesized SWNT solution. The sorting efficiency is similar to that of SWNTs dispersed with poly-3 dodecyl thiophene. We project that our material and device will be highly useful for future low-cost flexible photodetector applications.