Enhanced Photoelectrochemical Properties of Zn−Ag−In−Te Nanocrystals with High Energy Photon Excitation

Abstract

Multinary nanocrystals (NCs) of I‐III‐VI‐based semiconductors with less toxicity have attracted much attention for the fabrication of efficient light‐energy conversion systems. Here we report unique photoelectrochemical properties of ZnTe−AgInTe2 solid solution (ZAITe) NCs with a controllable energy gap in near‐IR region. The photoelectrochemical behavior of ZAITe NCs immobilized on an ITO electrode with a thickness of less than one monoparticle layer, resembling a p‐type semiconductor photoresponse, was remarkably different from that of ZAITe NC multilayer films: The onset of a cathodic photocurrent was shifted more positively than that of the valence band maximum of ZAITe NCs and the photocurrent generation efficiency was significantly increased, when photons with energy higher than ca. 2.5 eV were irradiated. These phenomena can be explained well by the direct hot hole transfer from ZAITe NCs to the ITO electrode.

Hot electron transfer in Zn–Ag–In–Te nanocrystal–methyl viologen complexes enhanced with higher-energy photon excitation

“…It was reported in our previous paper that multiple excitons could not be generated by the absorption of a single 3.1 eV-photon with a ZAITe NC despite an hn/E g ratio of 2.44. 34 Thus, the present results indicated that hot electrons, excited to a higher level with higherenergy photon absorption, could be more efficiently extracted with MV 2+ (Fig. 3c).…”

“…We previously reported that the level of the conduction band minimum (E CB ) of ZAITe NCs was À1.3 V vs. Ag/AgCl for the composition of x ¼ 0.75. 34 Since the redox potential of MV 2+ /MVc + , À0.65 V vs. Ag/AgCl, 35 was more positive than the E CB of ZAITe NCs used, excited electrons in the present ZAITe NCs were able to efficiently transfer to MV 2+ .…”

“…21 Recently, instead of using binary NCs showing high toxicity, such as CdSe, CdTe, and PbS, group I-III-VI semiconductor NCs have attracted increasing attention as light-absorbing materials with practical applications. [22][23][24][25][26][27][28][29][30][31][32][33][34] For example, Zhong et al reported that NCs composed of a Zn-Cu-In-Se solid solution, showing an absorption onset around 860-1060 nm, acted as efficient sensitizers for porous TiO 2 electrodes and that the resulting sensitized solar cells exhibited solar energy conversion efficiency of 11.6%. 28 We reported the preparation of Zn-Ag-In-Te (ZAITe) NCs with a rod shape, the energy gap (E g ) of which was enlarged from 1.20 to 1.60 eV with an increase in the Zn content.…”

“…28 We reported the preparation of Zn-Ag-In-Te (ZAITe) NCs with a rod shape, the energy gap (E g ) of which was enlarged from 1.20 to 1.60 eV with an increase in the Zn content. 27,32,34 The obtained ZAITe NCs exhibited a narrow bandedge photoluminescence (PL) peak with a high quantum yield of ca. 47%.…”

“…32 Furthermore, continuous light irradiation to ZAITe NC monolayers immobilized on ITO electrodes produced a cathodic photocurrent at an electrode potential more positive than that of their valence band edge, and then the observed photocurrent intensity increased with irradiation of higher-energy photons, indicating hot hole injection from ZAITe NCs to ITO electrodes. 34 By using transient absorption spectroscopy, the migration of hot carriers in NCs can be directly observed, enabling better clarication of the photochemical properties of I-III-VI-based NCs. However, compared to studies on conventional binary NCs, there have been few studies on charge extraction dynamics, especially for hot electrons photogenerated in I-III-VI-based NCs.…”