Photosensitivity Enhancement with TiO₂ in Semitransparent Light-Sensitive Skins of Nanocrystal Monolayers

Abstract

ABSTRACT:We propose and demonstrate light-sensitive nanocrystal skins that exhibit broadband sensitivity enhancement based on electron transfer to a thin TiO 2 film grown by atomic layer deposition. In these photosensors, which operate with no external bias, photogenerated electrons remain trapped inside the nanocrystals. These electrons generally recombine with the photogenerated holes that accumulate at the top interfacing contact, which leads to lower photovoltage buildup. Because favorable conduction band offset aids in transferring photoelectrons from CdTe nanocrystals to the TiO 2 layer, which decreases the exciton recombination probability, TiO 2 has been utilized as the electron-accepting material in these lightsensitive nanocrystal skins. A controlled interface thickness between the TiO 2 layer and the monolayer of CdTe nanocrystals enables a photovoltage buildup enhancement in the proposed nanostructure platform. With TiO 2 serving as the electron acceptor, we observed broadband sensitivity improvement across 350−475 nm, with an approximately 22% enhancement. Furthermore, time-resolved fluorescence measurements verified the electron transfer from the CdTe nanocrystals to the TiO 2 layer in light-sensitive skins. These results could pave the way for engineering nanocrystal-based light-sensing platforms, such as smart transparent windows, light-sensitive walls, and large-area optical detection systems.

Multiexciton generation assisted highly photosensitive CdHgTe nanocrystal skins

“…Larger NCs have larger number of states available, which result in higher optical absorption and thus higher voltage buildup. Secondly, small-sized NCs generally have a larger number of trap states than large-sized NCs, which hinder the migration of photogenerated positive charges [56,57]. Subsequently, the devices with the larger CdTe NCs show better performance and operate at longer wavelengths as it can be clearly seen from Fig.…”

Plasmon-Enhanced Energy Transfer in Photosensitive Nanocrystal Device

“…Details on the assembly procedures were explained in our previous works. 37,38 In this work, highly luminescent and stable CdSe/CdZnS NCs with diameters of 4.80 and 6.20 nm were synthesized following a modified recipe of W. K. Bae et al 39 as the donor and the acceptor NCs, respectively. As-synthesized NCs were ligand exchanged using negatively charged mercaptopropionic acid, which yielded stable NCs in aqueous solution (Supporting Information Figure S2).…”

“…The thickness of the PDDA–PSS bilayer was approximately 1.2 nm as verified by the optical ellipsometry measurement. Details on the assembly procedures were explained in our previous works. , In this work, highly luminescent and stable CdSe/CdZnS NCs with diameters of 4.80 and 6.20 nm were synthesized following a modified recipe of W. K. Bae et al . as the donor and the acceptor NCs, respectively.…”

Light-sensitive monolayer-thick nanocrystal skins of face-down self-oriented colloidal quantum wells

“…Furthermore, this device structure has also been demonstrated on various substrates, including semi-transparent and flexible substrates. [16][17][18][19][20][21][22] Finally, since the photogenerated voltage build-up allows for a self-powered operation mode, this device platform does not require any external power supply, making it highly attractive from the external power consumption point of view. 16 In this work, to utilize the attractive properties of CQWs and leverage on the orientation control in the self-assembly of CQW, we propose and demonstrate the LS-NS device platform of orientation controlled self-assembled 4.5 monolayers (ML) CdSe CQWs in the face-down orientation as the active layer, operating in the UV-visible range (Fig.…”