Metastable CdTe@HgTe Core@Shell Nanostructures Obtained by Partial Cation Exchange Evolve into Sintered CdTe Films Upon Annealing

Abstract

Partial Hg 2+ → Cd 2+ cation exchange (CE) reactions were exploited to transform colloidal CdTe nanocrystals (NCs, 4−6 nm in size) into CdTe@HgTe core@shell nanostructures. This was achieved by working under a slow CE rate, which limited the exchange to the surface of the CdTe NCs. In such nanostructures, when annealed at mild temperatures (as low as 200 °C), the HgTe shell sublimated or melted and the NCs sintered together, with the concomitant desorption of their surface ligands. At the end of this process, the annealed samples consisted of ligand-free CdTe sintered films containing an amount of Hg 2+ that was much lower than that of the starting CdTe@HgTe NCs. For example, the CdTe@HgTe NCs that initially contained 10% of Hg 2+ , after being annealed at 200 °C were transformed to CdTe sintered films containing only traces of Hg 2+ (less than 1%). This procedure was then used to fabricate a proof-of-concept CdTe-based photodetector exhibiting a photoresponse of up to 0.5 A/W and a detectivity of ca. 9 × 10 4 Jones under blue light illumination. Our strategy suggests that CE protocols might be exploited to lower the overall costs of production of CdTe thin films employed in photovoltaic technology, which are currently fabricated at high temperatures (above 350 °C), using post-process ligand-stripping steps.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

“…Instead, regarding the performance of the solar cell and comparing it with systems absorbing in the visible range, the PCE obtained is far from the results achieved with CsPbI 3 (13.4%) 76 or CdTe quantum dots (11.6%). 77 Considering the results from the photoconductor and solar cell, we could envision for our material a role in multilayer stacks operating as a charge transport layer with some additional photogeneration 62 , 63 rather than as the main active layer, whose band alignment can be favorably tuned by surface chemistry ( SI Section S.o ). Indeed, our material reaches a responsivity comparable to the ones of polymers (0.2–0.7 mA/W), 54 which are commonly used as charge transport layers.…”

“…The responsivity R = Iphoto/Popt (Iphoto = photocurrent, Popt = optical power on the device) was measured on 4 different devices to be R = 4±1 mA/W (best device 5 mA/W), The detectivity was (3±1)×10 8 Jones, estimated from the noise power density spectrum of a time trace acquired in the dark ( Figure S30). 66 We also evaluated the normalized photocurrent to dark current ratio NPDR = R/Idark (Idark = dark current), a suitable figure of merit in the case of devices with very low dark current. 67 In our case, we measured NPDR = (8.5 ± 2.8)×10 5 mW -1 .…”

Nanoscale AgInTe2/Si Truncated Quasitetrahedrons for Heterostructured Photodetectors

“…AgInTe 2 could also be capable of photoresponse and photodetection of incident light especially in NIR regions. For a long time, typical tellurides like CdTe and HgTe including their related alloys and composites have been successfully constructed as high-performance photodetectors. − Meanwhile, other different types of narrow-band-gap semiconductors, mainly including group IV elements Si − and Ge and group III–V compounds InSb and/or GaSb-based photoconductors, have been applied commercially in varied infrared regions. However, the absorption in the NIR region of silicon is restricted accompanied by undesirable photoelectronic performance for most of the silicon-based photodetectors due to its indirect band-gap nature and inferior efficiency of radiative transition .…”

Telluride Nanocrystals with Adjustable Amorphous Shell Thickness and Core–Shell Structure Modulation by Aqueous Cation Exchange

“…To further demonstrate the flexibility of the CER strategy for tailoring the NP surface and core@shell morphology, a second spontaneous CER with Hg 2+ achieved at 30 °C was applied to the as-prepared c@a-CdTe NP (synthesized at 80 °C). In recent years, many groups have reported the synthesis of Hg x Cd 1– x Te and CdTe@HgTe quantum dots by CER between CdTe and Hg 2+ . − In our reaction system, when introducing excess Hg 2+ to the as-prepared c@a-CdTe (80 °C) at 30 °C, Hg 2+ first reacted with the amorphous shell rather than the crystalline core (Figure ), which achieved a highly controlled c-CdTe@HgTe core–shell NP morphology, as characterized by XRD, STEM-ADF, and STEM–EDX analyses. The XRD spectrum matches well with cubic HgTe (PDF card number JCPDS no.…”