Abstract
Highly photoconductive thin films of inorganic-capped PbS nanocrystal quantum dots (QDs) are reported. Stable colloidal dispersions of (NH4)3AsS3-capped PbS QDs were processed by a conventional dip-coating technique into a thin homogeneous film of electronically coupled PbS QDs. Upon drying at 130 °C, (NH4)3AsS3 capping ligands were converted into a thin layer of As2S3, acting as an infrared-transparent semiconducting glue. Photodetectors obtained by depositing such films onto glass substrates with interdigitate electrode structures feature extremely high light responsivity and detectivity with values of more than 200 A/W and 1.2 × 1013 Jones, respectively, at infrared wavelengths up to 1400 nm. Importantly, these devices were fabricated and tested under ambient atmosphere. Using a set of time-resolved optoelectronic experiments, the important role played by the carrier trap states, presumably localized on the arsenic-sulfide surface coating, has been elucidated. Foremost, these traps enable a very high photoconductive gain of at least 200. The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra. These trap states also have an important impact on carrier dynamics, which led us to propose a kinetic model for trap state filling that consistently describes the experimental photoconductivity transients at various intensities of excitation light. This model also provides realistic values for the photoconductive gain and thus may serve as a useful tool to describe photoconductivity in nanocrystal-based solids.
Highlights
Colloidal semiconductor nanocrystals (NCs), known as colloidal quantum dots (QDs) due to their sizetunable optical and electronic properties, are highly appealing for applications in lightsensing devices operating in the visible,1À4 as well as in the near- and mid-infrared (IR),5À16 spectral regions
The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra
This has stimulated an immense interest in the development of IR-active NCs, including in their synthesis, surface functionalization, as well as their optical and electronic properties in colloidal solutions and in thin films.17À20 Despite the general notion that colloidal NCs are easy to process into devices by solution-based techniques, a common obstacle of this approach is the presence of bulky organic capping ligands on the NC surface after synthesis, which block the interparticle transport rendering all NC solids highly insulating
Summary
Colloidal semiconductor nanocrystals (NCs), known as colloidal quantum dots (QDs) due to their sizetunable optical and electronic properties, are highly appealing for applications in lightsensing devices operating in the visible,1À4 as well as in the near- and mid-infrared (IR),5À16 spectral regions. QDbased photodetectors that operate in the IR region beyond wavelengths of 1000 nm have no equivalent Si-based counterparts This has stimulated an immense interest in the development of IR-active NCs, including in their synthesis, surface functionalization, as well as their optical and electronic properties in colloidal solutions and in thin films.17À20 Despite the general notion that colloidal NCs are easy to process into devices by solution-based techniques (including spray-, spin-, dip- or drop-casting), a common obstacle of this approach is the presence of bulky organic capping ligands on the NC surface after synthesis, which block the interparticle transport rendering all NC solids highly insulating. In comparison to Naþ and Kþ sulfide-arsenite salts, the ammonium analogue, (NH4)3AsS3, can serve as a thermally degradable ligand, yielding arsenic(III) sulfide (As2S3) upon heating to 100 °C and above.[45]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
