Interface engineering has become a vital method in accelerating the development of perovskite solar cells in the past few years. To investigate the effect of different contacted surfaces of a light absorber with an electron transporting layer, TiO2, we synthesize CsPbBr3/TiO2 thin films with two different interfaces (CsBr/TiO2 and PbBr2/TiO2). Both interfacial heterostructures exhibit enhanced visible light absorption, and the CsBr/TiO2 thin film presents higher absorption than the PbBr2/TiO2 interface, which is attributed to the formation of interface states and the decreased interface bandgap. Furthermore, compared with the PbBr2/TiO2 interface, CsBr/TiO2 solar devices present larger output short circuit current and shorter photoluminescence decay time, which indicates that the CsBr contacting layer with TiO2 can better extract and separate the photo-induced carriers. The first-principles calculations confirm that, due to the existence of staggered gap (type II) offset junction and the interface states, the CsBr/TiO2 interface can more effectively separate the photo-induced carriers and thus drive the electron transfer from the CsPbBr3 perovskite layer to the TiO2 layer. These results may be beneficial to exploit the potential application of all-inorganic perovskite CsPbBr3-based solar cells through the interface engineering route.

Two-dimensional (2D) perovskites have been demonstrated great promise in x-ray detection application because of their stability, tunability, and the unique electronic properties. The centimeter-sized 2D perovskite (PMA)2PbI4 single crystal and the corresponding x-ray detector were fabricated. The Cu ion implanted device exhibits an excellent sensitivity of 283 μC Gyair−1 cm−2, the significantly enhanced mobility-lifetime (μτ) product of 8.05 × 10−3 cm2 V−1, and the lowest detectable dose rate of 2.13 μGyair s−1. Experimental observation combined with the DFT calculations shows that the improvement in Cu ion implanted x-ray detection is ascribed to the enhanced photoinduced charge carrier density and μτ product, and the increased carrier dissociation capability associated deeply with the decreased binding energy of exciton in the inorganic layer quasi-quantum well. The incorporation of the Cu interstitials by high-energy Cu ion implantation is able to introduce the donor and acceptor states with additional charge transfer channeling, resulting in the decreased exciton binding energy and fast dissociation of the exciton and the quick carrier extraction. Cu ion implantation regulating the dissociation of charge carriers in low-dimensional perovskites will motivate the application for 2D perovskite in high-performance x-ray detectors.

PbTiO 3 (PTO) is explored as a versatile and tunable electron-selective layer (ESL) for perovskite solar cells. To demonstrate effectiveness of PTO for electron-hole separation and charge transfer, perovskite solar cells are designed and fabricated in the laboratory with the PTO as the ESL. The cells achieve a power conversion efficiency (PCE) of ≈12.28% upon preliminary optimization. It is found that the PTO ferroelectric layer can not only increase the PCE, but also tune the photocurrent via tuning PTO's ferroelectric polarization. Moreover, to understand the physical mechanism underlying the carrier transport by the ferroelectric polarization, the electronic structure of PTO/CH 3 NH 3 PbI 3 heterostructure is computed using the first-principles methods, for which the triplet state is used to simulate charge transfer in the heterostructure. It is shown that the synergistic effect of type II band alignment and the specific ferroelectric polarization direction provide the effective extraction of electrons from the light absorber, while minimize recombination of photogenerated electronhole pairs. Overall, the ferroelectric PTO is a promising and tunable ESL for optimizing electron transport in the perovskite solar cells. The design offers a different strategy for altering direction of carrier transport in solar cells.

Functionalized graphene is widely used in various functional devices. Here, we introduce a simple plane capacity model and the density functional theory to investigate the origin of charge transfer in the graphene/CH 3 NH 3 PbI 3 interface, where graphene can be p-type or n-type doped by combining with different exposed surfaces of CH 3 NH 3 PbI 3 . Our calculations indicate that at the equilibrium distance, the work function of isolated graphene layer should be corrected by adding a value for assessing the charge transfer. After integrating the perovskite film with the functionalized graphene layer, we obtain a van der Waals heterostructure solar cell with a p−i−n configuration, which introduces a built-in electrical field to facilitate the separation and transport of the photogenerated carriers. The new p−i−n junction highlights the interface effect on graphene in solar cell, which offers an avenue to design new photovoltaic devices with high performance.

No abstract

No abstract

All-inorganic halide perovskite single crystals have attracted significant attention in optoelectronic fields on account of their outstanding optoelectronic properties. Photodetectors (PDs) based on CsPbBr 3 single crystal exhibit high responsivity (R) and external quantum efficiency (EQE) due to the direct optical band gap, large optical absorption throughout the visible spectrum range, and long-term stability. Herein, we prepared the centimetersize CsPbBr 3 perovskite single crystal and utilized Zr ion implantation to modify the photoelectric properties of single crystals. The optical band gap of the CsPbBr 3 single crystal decreases from 2.24 to 2.12 eV, and the absorption intensity increases after Zr ion implantation. The R and EQE of the CsPbBr 3 single crystal photodetector modified by Zr ion implantation are 1.0 A W −1 and 294%, respectively, with a light intensity of 3.8 mW cm −2 and a 5 V bias under 425 nm illumination, which are ten times larger than that of the pristine devices. Meanwhile, the first-principles calculation results show that the introduction of Zr ions decreases the band gap and that the Zr 4d orbit contributes to the conduction band minimum (CBM), which facilitates carrier transport in Zr ion implanted CsPbBr 3 single crystals. The results show that Zr ion implantation is an effective strategy to improve the performance of the CsPbBr 3 single-crystal-based PDs.

In this article, we provide the evidence of domain wall (DW) conduction in 90° BaZr0.1Ti0.9O3 (BZT) DWs by density functional theory (DFT) calculations. Experimental characterizations prove the existence of ferroelectric domains and DWs in as-prepared BZT films, and the measured electrical conductivity of the BZT films reaches ∼2.53 × 10−4 S/cm, which further confirms DW conduction. Furthermore, we designed BZT-based polarization tunable photovoltaic devices with DW conduction. The rearrangement of interfacial type-II band alignment upon different poling tends to regulate the charge transfer across the interface, confirmed by DFT calculations, resulting in a ferroelectric-tunable photovoltaic property. A positive polarization tends to improve the photovoltaic performance of the device, which has also been well verified in the experiments. Zr ion-implanted BaTiO3 provides a new route to fabricate an electronic transfer layer for high-efficiency perovskite solar cells. Our results reveal the mechanism of DW conduction, inspiring future improvements of photovoltaic devices which can be tuned by ferroelectric polarization.