Heterogeneous Integration of Colloidal Quantum Dot Inks on Silicon Enables Highly Efficient and Stable Infrared Photodetectors
Qiwei Xu, I Teng Cheong, Hanfa Song, Vien Van, Jonathan G. C. Veinot, Xihua Wang
Abstract
Integrating lead sulfide (PbS) colloidal quantum dots (CQDs) with crystalline silicon (c-Si) has been proven to be an effective strategy in extending the sensitivity of Si-based photodetectors into infrared regime. Here, we demonstrate the successful integration of PbS CQD inks with Si and construct a highly efficient heterojunction infrared photodiode operating in the range from 800 up to 1500 nm. Thanks to the well-passivated Si surface by a two-step chlorination/methylation method and high-quality CQD inks, the heterojunction photodiode yields a low density of trap states, as validated by transient photovoltage and photocurrent measurements. With an insertion layer of a p-type CQD capped with 1,2-ethanedithiol ligands, the built-in electric field is much enhanced, leading to improved charge extractions. As a result, we have obtained an external quantum efficiency (EQE) of 44% at the excitonic wavelength of 1280 nm. The EQE values are maintained without detectable degradation through the course of more than 600 h, achieving superior device stability. In contrast to commercial solutions, which require high-temperature epitaxial deposition of germanium (Ge) or III–V compounds, the presented single-step spin-coating process of CQD inks also enables large-area integration on Si.