Chemical Vapor-solution Fabrication Of Organometal Perovskite Thin Film And Its Optoelectronic Applicaitons

As a new candidate semiconductor material,organic-inorganic hybrid perovskite material employing CH3NH3PbI3 has attracted much attention and obtained a high performance in solar cells for its high absorption spectra,high carrier mobility and long charge diffusion length et.al.Up to now,the power conversion efficiency(PCE)of the perovskite solar cells have achieved to 22.1%,since the first reported in 2009 by solution process,meanwhile the deposition process is expanded to vapor process and vapor assisted solution process.However,except for the deposition process,the morphology of perovsktie film,electrons/holes transfer layer and the stability are also focused on improving the performance of perovskite devices.In this dissertation,we focus on the improving the performance of perovsktie devices by investigating the annealing temperature,morphology,the surface-activation and doping in the deposition process,which is based on the chemical vapor deposition process.In addition,a novel electron transfer layer is employed to realize the low-temperature,low-cost perovskite solar cells with their flexible devices.The main results and innovations of the dissertationas are as following aspects:1?The perovskite film has been widely used in thin film solar cell due to its wide absorption spectrum(ranging from 300 to 800nm),high carrier mobility,long exaction diffuse length and simple preparation.With the deep researching,the perovskite film now also applied in photodetectors.Herein,we employ the lower temperature and fast chemical vapor deposition process(LFCVD)to fabricate the perovskite film and investigate the morphology,crystallization and material phase of the perovskite in order to obtain a high responsitivity in zero bias.The responsitivity and the detectivity of the device are 0.55AW-1,?1012 Jones,respectively.The response time of the devices is estimated to 0.46?s/0.94p?s and the 3dB bandgap is up to 0.9MHz.In addition,a high PCE of 15.1%is achieved at the same time.Notably,the volume expansion during the perovskite formation reaction is found and the strain accumulated at the grain boundaries and the disintegration or the evaporation of CH3NH3I(MAI)will preferentially happen at the grain boundary regions during the expansion formation of the perovsktie grains with the annealing temperature increasing.After further investigation,we find that the thin PbI2 film provided the passivation at the interface and reduce the combination thus benefited the transportation of the charge,which can significantly improve the response speed.What's more,the vapor deposition process can effectively avoid the damage from the organic solvent and reduce the metastable state during the reaction,enhancing the stability of the devices.After stored in the air for more than two months,the devices still show a high response speed.2?Cadmium sulfide(CdS)has been widely used as electron transfer layer in the thin film solar cells and other electronic devices for its wide bandagap(-2.4eV),high carrier mobility and lower deposition temperature.We employ the CdS thin film by chemical bath deposition process(CBD)to replace the traditional inorganic semiconductor materials including Ti02,ZnO and Sn02 in the perovskite solar cells to realize the high power conversion efficiency with lower temperature.By investigating the different thickness of the CdS layer,we find that the best performance of the devices is obtained with a thickness of 50nm.And the Cl inclusion is detected during the chemical vapor deposition process(CVD)and makes a significant influence on the perovskite solar cells and a high PCE of 14.68%is achieved after the optimization of the thickness,temperature and deposition process.In addition,we also realized the CdS based perovskite solar cells with a high PCE of 9.93%on flexible substrates for the low synthesis temperature of CdS.As a traditional inorganic semiconductor material,CdS is not only a low cost electron transfer material but also providing a new enlightenment in flexible device for its lower synthesis temperature.3?The morphology of the absorption layer play an important role in perovskite film,and high crystallization and full coverage of the perovskite film are beneficial for the capture of the incent light.The morphology of the perovskite film is associated with the PbI2 film and the PbI2 film is difficult to control in traditional solution and vapor method.Herein,we propose a simple procedure—PbI2 power is dissolved in the DMF with NH4Cl to realized the dissolution in the room temperature.We can obtain the different morphologies of PbI2 film by adding various molar of NH4Cl,and a dense perovskite film with high crystallization is achieved after chemical vapor deposition process.At the same time,the Cl inclusion can also enhance the charge diffusion length by XRD and XPS analyzed.Finally,a high PCE of 16.42%is obtained with a molar ratio of 0.75 for NH4Cl and PbI2.4?The stability is an important issue for the perovskite thin film solar cells.And a high stability is beneficial for the applicaition in commercialization and industrial production.Herein,we introduce the CsBr into hybrid perovskite film via vapor deposition method to realize the vapor doping.Comparing to the traditional solution method,the content of Cs is well controlled by the thickness of CsBr film,which can not only avoid the influence of the organic solvent,but also realize the uniform distribution of Cs element.We find that the highest PCE of the devices is up to 18.22%with the thickness of CsBr near to lOnm.More important,the device shows a high stability and the PCE of the devices is still above 10%,after stored in the air for more than two months.