Unveiling Charge Carrier Recombination, Extraction, and Hot-Carrier Dynamics in Indium Incorporated Highly Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) have been propelled into the limelight over the past decade due to the rapid-growing power conversion efficiency (PCE). However, the internal defects and the interfacial energy level mismatch are detrimental to the device performance and stability. In this study, it is demonstrated that a small amount of indium (In3+ ) ions in mixed cation and halide perovskites can effectively passivate the defects, improve the energy-level alignment, and reduce the exciton binding energy. Additionally, it is confirmed that In3+ ions can significantly elevate the initial carrier temperature, slow down the hot-carrier cooling rate, and reduce the heat loss before carrier extraction. The device with 1.5% of incorporated In3+ achieves a PCE of 22.4% with a negligible hysteresis, which is significantly higher than that of undoped PSCs (20.3%). In addition, the unencapsulated PSCs achieve long-term stability, which retain 85% of the original PCE after 3,000 h of aging in dry air. The obtained results demonstrate and promote the development of practical, highly efficient, and stable hot-carrier-enhanced PSCs.

Regulation of the luminescence mechanism of two-dimensional tin halide perovskites.

Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly luminescent material. However, the research on the luminescence mechanism of this type of perovskite is still very controversial, which greatly limits the further improvement and application of the luminescence performance. At present, the focus of controversy is defects and phonon scattering rates. In this work, we combine the organic cation control engineering with temperature-dependent transient absorption spectroscopy to systematically study the interband exciton relaxation pathways in layered A2SnI4 (A = PEA+, BA+, HA+, and OA+) structures. It is revealed that exciton-phonon scattering and exciton-defect scattering have different effects on exciton relaxation. Our study further confirms that the deformation potential scattering by charged defects, not by the non-polar optical phonons, dominates the excitons interband relaxation, which is largely different from the Pb-based perovskites. These results enhance the understanding of the origin of the non-radiative pathway in Sn-based perovskite materials.

Electrochemical synthesis of annealing-free and highly stable black-phase CsPbI3 perovskite.

All-inorganic CsPbI3 halide perovskite has become a hot research topic for applications in next-generation optoelectronic devices. However, the main limitations are the high-temperature synthesis and poor phase stability. In this study, we demonstrate a unique solution-phase strategy for the low-temperature preparation of black-phase CsPbI3 by in situ electrochemistry. By controllable adjustment of the electrochemical growth process, annealing-free black-phase CsPbI3 can be synthesized. The black-phase CsPbI3 showed high-purity red photoluminescence at approximately 690 nm with ultra-high environmental stability for up to 11 days at a high relative humidity of 70%. The underlying mechanisms of the formation of the highly stable black-phase CsPbI3 at room temperature have been discussed in this study. The results provide a new platform for the large scale, low-temperature, and convenient synthesis of black-phase CsPbI3 perovskite.

Blue-Violet Emission with Near-Unity Photoluminescence Quantum Yield from Cu(I)-Doped Rb3InCl6 Single Crystals.

Low-dimensional metal halides have attracted considerable attention due to their unique optoelectronic properties. In this study, we report a solid-state synthesis of air-stable all-inorganic Pb-free zero-dimensional (0D) Rb3InCl6 single crystals (SCs). By a heterovalent doping of Cu+ ions, the Rb3InCl6:Cu+ SCs featured an efficient blue-violet emission with a greatly enhanced photoluminescence (PL) quantum yield (95%) and an ultralong PL lifetime (13.95 µs). Combined with temperature-dependent PL and density functional theory calculations, we conclude that the efficient electronic isolation, enhanced exciton-phonon coupling, and electronic structure modulation after doping lead to bright blue-violet emission. Furthermore, the SCs exhibited excellent stability, maintaining 90% of the initial PL intensity after being stored in ambient conditions for more than two months. The results provide a new strategy for improving the optoelectronic properties of 0D all-inorganic metal halides, which is promising for potential light-emitting applications.

A time- and angle-resolved photoemission spectroscopy with probe photon energy up to 6.7 eV.

We present the development of a time- and angle-resolved photoemission spectroscopy based on a Yb-based femtosecond laser and a hemispherical electron analyzer. The energy of the pump photon is tunable between 1.4 and 1.9 eV, and the pulse duration is around 30 fs. We use a KBe2BO3F2 nonlinear optical crystal to generate probe pulses, of which the photon energy is up to 6.7 eV, and obtain an overall time resolution of 1 ps and energy resolution of 18 meV. In addition, ß-BaB2O4 crystals are used to generate alternative probe pulses at 6.05 eV, giving an overall time resolution of 130 fs and energy resolution of 19 meV. We illustrate the performance of the system with representative data on several samples (Bi2Se3, YbCd2Sb2, and FeSe).