Highly Stable,Lead-free Copper(Ⅱ)-based Organic-inorganic Hybrid Light Absorber And The Photovoltaic Devices

Perovskite solar cells are presently attracting immense research interest on the global level due to the dramatic rise of their power conversion efficiency（PCE）from3.8% to a certified value of 22.1% over the past serveral years.However,the perovskite absorbers are still facing two possible crucial issues for the commercialization: the use of environmentally hazardous lead and the poor stability of perovskite absorbers.To address these critical issues,we present a lead-free,highly stable C₆H₄NH₂CuBr₂I compound.Moreover,C₆H₄NH₂CuBr₂I-based fully printable mesoscopic solar cell with a preliminary PCE of ⁰.5% was achieved.This work demonstrates an alternative pathway to develop low-toxic and highly stable organic-inorganic hybrid materials for solar cell applications.The main contents and results are summarized as following:（1）The preparation and crystal structure characterization of C₆H₄NH₂CuBr₂I compoundC₆H₄NH₂CuBr₂I polycrystalline powder was prepared by mechnochemistry approach.The chemical composition of the resulted sample was determined by energy-dispersive X-ray spectroscopy（EDS）.The crystal structure was investigated by powder X-ray diffraction（PXRD）and high-resolution transmission electron microscope（TEM）.It is found that the resulting C₆H₄NH₂CuBr₂I sample crystallizes into a hexagonal space group R3,with a = b = 3.963（3）?,c = 9.698（5）?,Z = 3 and the ratio of copper and halogen is about 1:3.（2）The humidity-and thermal-stability of C₆H₄NH₂CuBr₂I compoundThe contact angle and thermal-stability of C₆H₄NH₂CuBr₂I compound were investigated by the contact angle measurements and thermo gravimetric analysis（TGA）.C₆H₄NH₂CuBr₂I compound not only exhibits hydrophobic behavior with a contact angle of ⁹0°,but also displays high thermal-stability with a beginning of weight loss at ¹33°C.Besides,the UV-Vis absorption spectrum measurements of the C₆H₄NH₂CuBr₂I thin film were carried out before and after dropping water on the film surface for several minutes;no obvious changes were observed.Most strikingly,the XRD patterns remain nearly the same even after 4 h of immersing C₆H₄NH₂CuBr₂I film in water.Our results demonstrate that C₆H₄NH₂CuBr₂I compound is a humidity-and thermal-stable material.（3）The optoelectronic and photovoltaic properties of C₆H₄NH₂CuBr₂I-based solar cellsThe optoelectronic properties of C₆H₄NH₂CuBr₂I compound were investigated by the UV-Vis spectroscopy,transmission spectrum,photoluminescence spectrum（PL）and ultraviolet photoelectron spectroscopy（UPS）.C₆H₄NH₂CuBr₂I thin film exhibits a Eg of ¹.64 eV and a PL peak of ¹.50 eV.The absorption coefficient of C₆H₄NH₂CuBr₂I compound is estimated to ⁶×104 cm-1 at 450 nm.The Fermi energy（EF）and valence band energy（Ev）were found to be-4.90 eV and-6.4 eV,respectively.The copper-based light absorber was then applied in printable mescoscopic solar cell based on carbon back-contact.Furthermore,the current density-voltage（J-V）curves were measured under simulated AM1.5 100 m W cm-2illumination.A preliminary PCE of ⁰.5% was achieved with a photocurrent density（Jsc）of ⁶.20 mA cm-2,an open-circuit voltage（Voc）of 0.20 V and a fill factor（FF）of0.46.