New Lead-free Organic-Inorganic Hybrid Semiconductor Single Crystals for a UV-Vis-NIR Broadband Photodetector.

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn2+ oxidation. Herein, a novel, non-toxic, and solution-processed millimeter-sized OIHS single crystal [Ga(C3H7NO)6](I3)3 has been grown at room temperature. Both the absorption measurement and density functional theory calculations have confirmed a narrow indirect band gap of 1.32 eV. The corresponding photodetector based on this single crystal demonstrated excellent performance including an ultraviolet-visible-near infrared (UV-vis-NIR) response between 325 and 1064 nm, fast response time (trise/tdecay = 3.8 ms/5.4 ms), and profound air storage stability (41 h), thus outperforming most common photodetectors based on Sn-based perovskites. This work not only provides a profound understanding of this novel organic-inorganic single-crystal material but also demonstrates its great potential to realize the high-performance UV-vis-NIR broadband photodetectors.

Interfacial Investigation on Printable Carbon-Based Mesoscopic Perovskite Solar Cells with NiOx/C Back Electrode.

Solar cells with high efficiency, low cost, and high stability are the target for the new generation of solar cells. A fully printable perovskite (CH3NH3PbI3) solar cell (PSC) with device architecture FTO/TiO2/Al2O3/NiOx/C is fabricated in the current research as a low-cost and relatively stable structure and is investigated to determine how different fabrication factors such as the thickness of the insulating spacer layer (Al2O3) or treatments such as heat and UV-O3 treatments can affect the interfacial properties of this multilayer mesoporous structure. X-ray photoelectron spectra (XPS) show that UV-O3 treatment increases the Ni3+(Ni2O3) phase on the surface of the black nickel oxide layer leading to better charge extraction and increasing open-circuit voltage (VOC) up to 0.945 V. We observe improved CH3NH3PbI3 formation inside the mesoporous layers by the PbI2 penetration at a higher temperature. Impedance spectral together with current-voltage measurements show the effect of thickness for the insulator layer in the internal and interfacial resistances and photovoltaic characteristics of the cell. The best performance of the carbon-based PSC attains power conversion efficiency of 12.1% with the thickness of the Al2O3 layer at 450 nm.