Preparation Of Hybrid Cationic Perovskite Solar Cells And Research On Their Photovoltaic Performances

As a rising star in the field of third-generation novel solar cells,perovskite solar cells（PSCs）were first reported by Professor Tsutomu Miyasaka of Japan in 2009,which opened the prelude to study of PSCs and aroused widespread concern in academcic circles.After nearly a decade of research,PSCs have made breakthrough progress,which is attributed to the excellent characteristics of perovskite materials,including a suitable and adjustable bandgap,balanced carrier mobility,high optical absorption coefficient,long carrier transport distance,simple preparation technology and other advantages.The traditional perovskite solar cell structure is composed of conductive glass,electronic transporting layer,perovskite absorption layer,hole-transporting layer and a metal electrode.Among them,Au,which is used as a metal counter electrode,is not only expensive,but also easy to ionize and react with perovskite material after diffusion.Spiro-OMe TAD is an unstable and costly organic hole-transporting material.These two factors will affect the stability of devices and increase the cost of manufactation,which seriously restrict the industrial development of PSCs.In this paper,the starting point is to reduce the cost and improve the stability of PSCs,which using cheap and abundant carbon materials to replace Au as the back electrode,and useing mixed cation perovskite as the absorption layer.Meanwhile,the perovskite material can be used for both electronic transporting and hole-transporting to simplify the process,and prepared PSCs with a structure of FTO/Ti O₂dense layer/Ti O₂mesoporous layer/perovskite/C electrode.The specific research work and results are summarized as follows:（1）The research and preparation of compact layer,mesoporous layer and back electrode was studied.At a low speed of 500 rpm for 3 s and a high speed of 3000 rpm for 30s,Ti O₂compact layer was prepared by spin-coated the mixed solution of n-butanol and diisopropoxydiacetylacetone titanium with a mass ratio of 1:10.3.SEM shows that the Ti O₂compact layer has good density,no cracks and holes,which is conducive to electronic transmission;XRD pattern shows that the Ti O₂compact layer is anatase structure,suitable for preparing high-performance PSCs.Under the condition of speed of 5000 rpm and 30s,spin-coating a mixed solution of 30-NRT Ti O₂and absolute ethanol with a mass ratio of1:4.1 to prepared Ti O₂mesoporous layer.SEM characterization shows that the Ti O₂mesoporous layer has a porous structure,which provides a scaffold for the growth and crystallization of perovskite,and also plays a role in transporting electrons.The carbon film is prepared as the back electrode of the battery by a simple knife coating method.（2）Preparation of mixed cationic FA_xMA_1-xPb I₃perovskite films and research on their microstructure and optical properties.The FA_xMA_1-xPb I₃（x=0.1,0.2,0.3,0.4,0.6,0.8,1.0）films was prepared by an anti-solvent one-step method with adjust the molar ratio of FAI and MAI in the precursor solution.On the one hand,with the increase of FA⁺content,the grain size gradually increases and the diffraction peak has a slight left-shift.Since the size of FA⁺（0.279 nm）is larger than MA⁺（0.270 nm）,and when more FA⁺ions replace MA⁺ions,the lattice size of perovskite increases gradually.According to the Bragg equation 2dsinθ=n?,the diffraction angle decreases with the increase of crystal lattice.On the other hand,the optical band gap of FAPb I₃（1.43 e V）is smaller than that of MAPb I₃（1.55 e V）.With the increase of FA⁺content,the absorption peak and PL emission peak of the films are red-shifted.（3）Research on photovoltaic performance,charge transport performance and stability of PSCs based on FA_xMA_1-xPb I₃.All PSCs exihibit a better performance than pure FAPb I₃,and their PCE is improved from 3.26%to 8.77%.In particular,the PSC based on FA_0.4MA_0.6Pb I₃exhibit the lowest series resistance（R_s）and charge transfer resistance(R_ct),which has an optimal photovoltaic performance:short-circuit current density of 22.84m A/cm²,open-circuit voltage of 0.80 V,fill factor of 0.48,and power conversion efficiency of 8.77%.Moreover,the battery remained 75.8%of its initial efficiency,which stability is improved after exposure to ambient air conditions for over 670 h.（4）Preparation of mixed cation Cs_xMA_1-xPb I₃perovskite films and research on their microstructure and optical properties.An antisolvent-assisted one-step method was used to prepare the mixed cation Cs_xMA_1-xPb I₃（x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0）perovskite films.The addition of trace Cs is beneficial to improve the compactness of the films.In addition,compared with the pure MAPb I₃film,as the Cs⁺content increases,the absorption edge of the Cs_xMA_1-xPb I₃films gradually shift to shorter wavelengths,because MAPb I₃（1.58 e V）and?-Cs Pb I₃（1.73 e V）have different optical bandgap.The Cs_xMA_1-xPb I₃films with high content of Cs⁺（x?0.4）show a clear absorption peak at 450 nm,which is manifested as?-Cs Pb I₃（2.82 e V）with a photovoltaic inactivity.（5）Research on photovoltaic performance,charge transport performance and stability of Cs_xMA_1-xPb I₃perovskite solar cells.Compared with pure PSC based on MAPb I₃,when the content of Cs⁺is x=0.1,the PCE of Cs_xMA_1-xPb I₃increases from 8.11%to 11.59%.And the PSC has a great contact at the perovskite/carbon interface,resulting in a better short-circuit current density and filling factor of 22.83 m A/cm²and 0.54,respectively.At the same time,its PCE still maintained 96.7%and 81.9%of the initial efficiency after being exposed to ambient air conditions for 168 hours and 384 hours,respectively.