We present the photodetection properties of graphene/Si heterojunctions both in the photocurrent and photovoltage modes. Monolayer graphene/Si junctions were found to be excellent weak-signal detectors with photovoltage responsivity exceeding 10(7) V/W and with noise-equivalent-power reaching ∼1 pW/Hz(1/2), potentially capable of distinguishing materials with transmittance, T = 0.9995 in a 0.5 s integration time. In the photocurrent mode, the response was found to remain linear over at least six decades of incident power (P), with tunable responsivity up to 435 mA/W (corresponding to incident photon conversion efficiency (IPCE) > 65%) obtained by layer thickening and doping. With millisecond-scale responses and ON/OFF ratios exceeding 10(4), these photodiodes are highly suitable for tunable and scalable broadband (400 < λ < 900 nm) photodetectors, photometers, and millisecond-response switching, spectroscopic and imaging devices, and further, and are architecturally compatible with on-chip low-power optoelectronics.

Here, we present the fifth member (n = 5) of the Ruddlesden-Popper (CH 3 (CH 2) 3 NH 3) 2 (CH 3 NH 3) nÀ1 Pb n I 3n+1 family, which we successfully synthesized in high yield and purity. Phase purity could be clearly determined from its X-ray powder diffraction patterns, which feature the (0k0) Bragg reflections at low 2q angles. The obtained pure n = 5 compound was confirmed to be a direct bandgap semiconductor with E g = 1.83 eV. The direct nature of the band gap is supported by density functional theory calculations. Intense photoluminescence was observed at room temperature at 678 nm arising from the band edge of the material. High-quality thin films can be prepared by the hot-casting method from solutions with a pure-phase compound as a precursor. The planar solar cells fabricated with n = 5 thin films demonstrate excellent power-conversion efficiency of 8.71% with an impressive open-circuit voltage of $1 V. Our results point to the use of layered perovskites with higher n numbers and pure chemical composition.

International audience2D Ruddlesden–Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power-conversion efficiencies (PCEs) of over 10% with technologically relevant stability. To achieve solar cell performance comparable to the state-of-the-art 3D perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near-IR region absorption by increasing the perovskite slab thickness. Here, the use of the 2D higher member (n = 5) RP perovskite (n-butyl-NH3)2(MeNH3)4Pb5I16 in depositing highly oriented thin films from dimethylformamide/dimethylsulfoxide mixtures using the hot-casting method is reported. In addition, they exhibit superior environmental stability over thin films of their 3D counterpart. These films are assembled into high-efficiency solar cells with an open-circuit voltage of ≈1 V and PCE of up to 10%. This is achieved by fine-tuning the solvent ratio, crystal growth orientation, and grain size in the thin films. The enhanced performance of the optimized devices is ascribed to the growth of micrometer-sized grains as opposed to more typically obtained nanometer grain size and highly crystalline, densely packed microstructures with the majority of the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X-ray diffraction and grazing-incidence wide-angle X-ray scattering mapping

Hybrid perovskites are on a trajectory toward realizing the most efficient single-junction, solution-processed photovoltaic devices. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance and photostability. Here, the controlled growth of hybrid perovskites on nickel oxide (NiO) is shown, resulting in the formation of thin films with enhanced crystallinity with characteristic peak width and splitting reminiscent of the tetragonal phase in single crystals. Photophysical and interface sensitive measurements reveal a reduced trap density at the perovskite/NiO interface in comparison with perovskites grown on poly(3,4-ethylene dioxy thiophene) polystyrene sulfonate. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a near-ideal energy band alignment. Moreover, photostability of photovoltaic devices up to 10-Suns is observed, which is a direct result of the superior crystallinity of perovskite thin films on NiO. These results elucidate the critical role of the quality of the perovskite/hole transport layer interface in rendering high-performance and photostable optoelectronic devices.

Solid-state radiation detectors, using crystalline semiconductors to convert radiation photons to electrical charges, outperform other technologies with high detectivity and sensitivity. Here, we demonstrate a thin-film x-ray detector comprised with highly crystalline two-dimensional Ruddlesden-Popper phase layered perovskites fabricated in a fully depleted p-i-n architecture. It shows high diode resistivity of 1012 ohm·cm in reverse-bias regime leading to a high x-ray detecting sensitivity up to 0.276 C Gyair−1 cm−3. Such high signal is collected by the built-in potential underpinning operation of primary photocurrent device with robust operation. The detectors generate substantial x-ray photon–induced open-circuit voltages that offer an alternative detecting mechanism. Our findings suggest a new generation of x-ray detectors based on low-cost layered perovskite thin films for future x-ray imaging technologies.