Interface And Crystallization Control For The Performance Research Of Flexible Perovskite Solar Cells

With the increasing demand for smart wearable electronic devices,flexible perovskite solar cells are attracting the researchers’ attention due to their advantages of light weight,enabling fabrication by solution processing,low cost,and can be integrated with flexible electronic devices.However,the poor crystal quality of flexible perovskite films,high interfacial defect density and recombination rate,as well as poor mechanical stability of devices have greatly restricted the development of flexible perovskite photovoltaic devices in the largescale application.Therefore,this study focused on the enhancement of the crystalline quality and mechanical stability of flexible perovskite films.The methods of the interface and crystallization control combined with ink engineering are used to achieve the fabrication of high-performance flexible perovskite solar cells.The main research contents and results of this paper are as follows:(1)Appropriate interfacial transport layer can effectively improve the extraction efficiency of the photogenerated charge in perovskite films.In this paper,Al-doped ZnO(AZO)electron transport layer is prepared and applied in flexible all-inorganic perovskite solar cells for the first time.The doping of Al can effectively passivates the oxygen defects in ZnO,which is beatific to the highly uniform and dense perovskite films.Compared with common ZnO and SnO2 electron transport layers,the energy level of AZO is more compatible with CsPbI2Br perovskite,which can improve the charge transfer of the device and increase its open-circuit voltage.Finally,a flexible all-inorganic perovskite solar cell based on AZO interface layer achieved an open circuit voltage of 1.25V and a power conversion efficiency of 12.74%.(2)To further improve the efficiency and stability of flexible all-inorganic perovskite solar cells,a small molecule with cyanide group(t-BCA)is added to the upper layer of inorganic perovskite films as an interfacial passivation layer.The influence of the t-BCA layer on the quality and interfacial transport performance of perovskite films are systematically analyzed by a series of measurements.It can be found that the cyanide group in t-BCA chelates with the lead vacancy in perovskite,passivating the interface defects of the film and greatly inhibiting the non-radiation recombination.Thus,the efficiency and environmental stability of the flexible devices are improved.By exploring the preparation process of the passivation layer,the conversion efficiency of flexible CsPbI2Br perovskite cells is up to 15.08%.In addition,the optimization of the quality of perovskite film and the use of thick-insensitive AZO can also enhance the mechanical stability of flexible devices.(3)Additive assisted crystallization in precursor ink is a common method to prepare high-quality perovskite film.However,the addition of additives always tends to reduce the printability of perovskite ink,which is not beneficial for the printing of large-area perovskite film.In this work,a liquid crystal molecule with temperature response functions is added to the perovskite precursor ink.It is confirmed that the addition of liquid crystal molecules can improve the quality of perovskite films and effectively enhance the large-area printability of perovskite ink.The crystal orientation of liquid crystal molecules in specific phase states can be used as templates to induce the oriented crystallization of perovskite,and passivate the grain boundary defects of the perovskite film.The optimized flexible perovskite devices with 6OBA exhibit superior power conversion efficiency of 19.87%(1.01 cm2)and 14.74%(25 cm2).Moreover,due to the specific structure of 6OBA and the enhanced quality of perovskite films,the residual stress of the film is efficiently released.The flexible perovskite solar cell exhibit outstanding bending resistance,retaining over 88%of its initial efficiency after 1000 bending cycles at a radius of 3 mm.This work provides a facile strategy for accelerating the development of flexible electronics.(4)Previous studies show that environmental degradation and ductile cracks of perovskite films usually begin at the grain boundaries(GBs).Herein,sulfonated graphene oxide(s-GO)is employed to construct cementitious GBs by interacting with the[PbI6]4-at GBs.The resultant s-GO-[PbI6]4-complex can effectively passivate the defects of vacant iodine,and the devices with s-GO exhibit remarkable waterproofness and flexibility due to the tough and waterinsoluble GBs.The champion PCE of 20.56%(1.01 cm2)in a device treated with s-GO is achieved.This device retains 80%of its original PCE after 10,000 bending cycles at a curvature radius of 3 mm.