Thiocyanate-anion (SCN⁻) two-dimensional (2D) layered perovskite with internal stress-controlled nano phase segregation has been firstly demonstrated as a promising material system for luminescence applications. An interesting energy band structure is found as well as charge transfer process caused by nano phase segregation, which provide an alternative route to overcome the indirect-bandgap luminescence limit of SCN layered perovskites. It is revealed that, within the SCN layered framework, the segregated nano phases exist in a quantum well form, possessing much higher carrier localization and second-order radiative recombination abilities. With the help of internal stress modulation, these advantages can be significantly enhanced and finally contribute to high luminescence performances in visible-red regions. This work provides more potential opportunities for 2D layered perovskite materials in the future optoelectronic applications.

Sodium-doped carbon nitride nanotubes (Na_x -CNNTs) were prepared by a green and simple two-step method and applied in photocatalytic water splitting for the first time. Transmission electron microscopy (TEM) element mapping and X-ray photoelectron spectroscopy (XPS) measurements confirm that sodium was successfully introduced in the carbon nitride nanotubes (CNNTs), and the intrinsic structure of graphitic carbon nitride (g-C₃N₄) was also maintained in the products. Moreover, the porous structure of the CNNTs leads to relatively large specific surface areas. Photocatalytic tests indicate that the porous tubular structure and Na⁺ doping can synergistically enhance the hydrogen evolution rate under visible light (λ > 420 nm) irradiation in the presence of sacrificial agents, leading to a hydrogen evolution rate as high as 143 μmol·h^-1 (20 mg catalyst). Moreover, other alkali metal-doped CNNTs, such as Li_x -CNNTs and K_x -CNNTs, were tested; both materials were found to enhance the hydrogen evolution rate, but to a lower extent compared with the Na_x -CNNTs. This highlights the general applicability of the present method to prepare alkali metal-doped CNNTs; a preliminary mechanism for the photocatalytic hydrogen evolution reaction in the Na_x -CNNTs is also proposed.

Heterojunction interfaces in perovskite solar cells play an important role in enhancing their photoelectric properties and stability. Till date, the precise lattice arrangement at TiO₂/CH₃NH₃PbI₃ heterojunction interfaces has not been investigated clearly. Here, we examined a TiO₂/CH₃NH₃PbI₃ interface and found that a heavy atomic layer exists in such interfaces, which is attributed to the vacancies of methylammonium (MA) cation groups. Further, first-principles calculation results suggested that an MA cation-deficient surface structure is beneficial for a strong heterogeneous binding between TiO₂ and CH₃NH₃PbI₃ to enhance the interface stability. Our research is helpful for further understanding the detailed interface atom arrangements and provides references for interfacial modification in perovskite solar cells.

CH₃NH₃PbI₃ perovskite solar cells with 2TPA-n-DP (TPA = 4, 4′-((1E, 1′E, 3E, 3′E)-[1, 1′-biphenyl]-4, 4′-diylbis(buta-1, 3-diene-4, 1-diyl)); DP = bis(N, N-di-p-tolylaniline); n = 1, 2, 3, 4) as hole-transporting materials (HTMs) have been fabricated. After optimization of the mesoporous TiO₂ film thickness, devices based on 2TPA-2-DP with power conversion efficiencies (PCEs) of up to 12.96% have been achieved, comparable to those of devices with (2, 2′, 7, 7′-tetrakis(N, N-di-p-methoxyphenylamine)-9, 9′-spirobifluorene) (spiro-OMeTAD) as HTM under similar conditions. Further time-resolved photoluminescence (PL) measurements showed a fast charge transfer process at the perovskite/2TPA-2-DP interface. With the aid of electrochemical impedance spectra, a study of the electron blocking ability of 2TPA-2-DP in the device reveals that the presence of 2TPA-2-DP can greatly increase charge transfer resistance at the HTM/Au interface in the device, thus reducing the recombination. Furthermore, the perovskite solar cells based on these four HTMs exhibit good stability after testing for one month.