possess lower dark currents and higher detectivities. In spite of great progresses, it is complicated to fabricate composite electronic transport layers (ETLs) with matched crystal lattices and energy levels, otherwise the newly formed interface in the composite may bring about large amounts of defects which act as trap sites and recombination centers.Spatially graded composition (bandgap) is an effective route to continuously tune energy levels and bandgap in semiconductors, [20,21] in which the interfacial recombination is alleviated or removed and a graded built-in potential through the whole bulk is produced, enabling stronger separation capability of photogenerated electron-hole pairs. This concept provides a new platform for designing high-performance optoelectronic devices. For example, Krol and co-workers fabricated the gradient W-doped BiVO 4 as a photoanode of photoelectrochemical cell. [22] Compared to the homogeneously doped BiVO 4 , the continuous built-in band bending induces the directional transfer of photogenerated holes from core to surface and thus increases the carrier separation efficiency to 60%. Tailoring the gradient bandgap from 0.35 to 1.42 eV, Pan and co-workers synthesized InAs x P 1-x nanosheets for band-selective infrared photodetectors. [23] We reported graded CdS x Se 1-x nanobelt solar cells by utilizing continuous stepped energy levels to drive electrons and holes toward opposite direction. [24] In p-i-n structured devices, [25][26][27][28] graded composition (bandgap) is basically used in the main photosensitive layer, for which the narrow bandgap region increases the absorption wavelength range, the large bandgap results in a high voltage output, and graded bandgap structure promotes the carriers transport. Inspired by previous results, with the introduction of gradient built-in band bending at the charge extraction layer/perovskite interface, the energy band offset is expected to provide the driving force for enhanced carrier separation, suppressed electron reflux, and reduced recombination, boosting the performance of perovskite photodetectors.In this work, we present a high-performance self-powered photodetector by integrating perovskite with gradient O-doped CdS nanorod array. For the first time, the continuous builtin band bending is introduced at the charge extraction layer/ perovskite interface to manipulate the transfer behavior of carriers in perovskite photodetectors. The optoelectronic measurements reveal that both the responsivity and the response speed of devices strongly depend on the structure of energy band bending. The optimum gradient O-doped CdS/perovskite Self-powered photodetectors are highly desired to meet the great demand in applications of sensing, communication, and imaging. Manipulating the carrier separation and recombination is critical to achieve high performance. In this paper, a self-powered photodetector based on the integrated gradient O-doped CdS nanorod array and perovskite is presented. Through optimizing the degree of continuous built-in ba...

The Z‐scheme heterojunction has great potential in photoelectrochemical (PEC) water splitting due to its unique charge‐carrier migration pathway, superior carrier separation efficiency, and high redox capacity, but how to regulate the Z‐scheme charge transfer at the nanometric interface of heterostructures still remains a big challenge. Herein, InOCd bond is rationally introduced at the interface between ZnIn2S4 nanosheets and CdS nanoparticles through a facile cation exchange reaction, which successfully converts the previously reported type II band structure to a direct Z‐scheme heterojunction (ZnIn2S4/CdS) as confirmed by various characterizations. Density functional theory calculation reveals that the InOCd interfacial chemical bond significantly uplifts the Fermi level of ZnIn2S4 and CdS, inverts the interfacial band bending direction, thus resulting in the formation of Z‐scheme heterojunction. Moreover, an amorphous ZnO overlayer is deposited to eliminate the surface defects and accelerate the surface reaction kinetics. Benefiting from the superior charge separation efficiency and high redox ability originating from the Z‐scheme structure, the optimum ZnIn2S4/CdS/ZnO photoanode exhibits a dramatically enhanced PEC performance with low onset potential (−0.03 V vs reversible hydrogen electrode, VRHE) and large photocurrent of 3.48 mA cm−2 at 1.23 VRHE, which is about 21.75 times that of pristine ZnIn2S4.

friendly properties. [6] However, due to its severe bulk carrier recombination, unfavorable carrier transportation, and sluggish surface OER dynamics, the PEC performance of bare ZnIn 2 S 4 photoanode is still not satisfactory.Various strategies have been developed to enhance the PEC performance of ZnIn 2 S 4 , such as morphology engineering, constructing heterojunctions, and coating surface co-catalysts, etc. [7][8][9] Among them, decorating surface cocatalysts has been considered as an effective strategy to promote surface water oxidation kinetics of pristine ZnIn 2 S 4 . However, the integration of water-oxidation cocatalysts with PEC photoanodes has been limited to metal-based materials, such Co-Pi, FeCoO x , and FeOOH. [10][11][12][13][14][15] The cocatalysts containing metallic ions tend to be toxic and expensive, which could limit their further applications. In addition, these cocatalysts may cause light absorption attenuation and increased charge recombination due to the large thickness/dimension of cocatalysts and additional interface defects between cocatalysts and photo anodes. Recently, nonmetallic anionic groups, such as phosphate (PO 4 3− ), selenate (SeO 4 2− ), and sulfate (SO 4 2− ), have emerged as alternatives to boost water oxidation ability. [16][17][18] These nonmetallic groups could optimize the electronic structure of active sites, regulate the adsorption of intermediates to reduce OER overpotential, and promote the surface carrier transfer. Particularly, the SO 4 2− group can break the adsorption-energy scaling relation between OH* and OOH* (reaction intermediates) and decrease the OER overpotential. [17] Accordingly, engineering ZnIn 2 S 4 with SO 4 2− groups is a promising strategy to improve its surface reaction kinetics. However, the introduction of nonmetallic anionic groups usually relies on a direct mixing method or external addition, which leads to weak chemical interaction and thus decreases the effectiveness and durability of the resultant materials. [17] In contrast, in situ introducing SO 4 2− anionic groups into ZnIn 2 S 4 to induce strong bonding between anions and metal atoms is expected to remarkably facilitate solar water oxidation.As a kind of intrinsic defect for metal sulfide, sulfur vacancies (S v ) have the ability to adjust the electronic structure of metal sulfide, leading to optimization of the adsorption free energy and also improvement of the conductivity. [19,20] S v can be divided into bulk S v and surface S v according to their spatial Severe charge recombination and slow surface water oxidation kinetics seriously limit the practical application of ZnIn 2 S 4 photoanodes for photo electrochemical water splitting. Herein, an in situ strategy to introduce sulfate (SO 4 2− ) anions and controlled bulk sulfur vacancies (S v ) into a ZnIn 2 S 4 photoanode is developed, and its PEC performance is remarkably enhanced, achieving a photocurrent density of 3.52 mA cm −2 at 1.23 V versus reversible hydrogen electrode (V RHE ) and negatively shifted onset potential of 0....

The facile hydrothermal synthesis of Zn10In16S34 atomically thin nanosheet arrays on fluorine‐doped tin oxide glass (FTO) substrates is presented. Through controlling heat treatment in air, O‐doping and Zn, S vacancies were simultaneously introduced in Zn10In16S34 nanosheets with adjusted phase, morphology, chemical compositions, and energy level distribution. The surface defect states are passivated by depositing ultrathin Al2O3 film by atomic layer deposition technology. The performance of Zn10In16S34 photoanodes is largely improved, with 4.7 times higher current density and reduced onset potential. The experimental results and density functional theory calculations indicate that the enhancement is attributed to the fast photoexcited electron–hole pair separation, decreased surface transfer impedance, prolonged carrier lifetime, and reduced overpotential of oxygen evolution reaction.

Photoelectrochemical (PEC) water splitting is a promising strategy to convert solar energy into hydrogen fuel. However, the poor bulk charge‐separation ability and slow surface oxygen evolution reaction (OER) dynamics of photoelectrodes impede the performance. We construct In‐ and Zn/In‐doped SnS2 nanosheet arrays through a hydrothermal method. The doping induces the simultaneous formation of an amorphous layer, S vacancies, and a gradient energy band. This leads to elevated carrier concentrations, an increased number of surface‐reaction sites, accelerated surface‐OER kinetics, and an enhanced bulk‐carrier separation efficiency with a decreased recombination rate. This efficient doping strategy allows to manipulate the morphology, crystallinity, and band structure of photoelectrodes for an improved PEC performance.