Research On BHT And KSeCN Additives To Regulate Perovskite Thin Films And Perovskite Solar Cells

Perovskite is a kind of organic-inorganic hybrid metal halide material.Perovskite materials have the advantages of high light absorption,carrier mobility and wide material sources.The planar structure perovskite solar cell based on this excellent material has low open pressure loss and high photoelectric conversion efficiency.Its photoelectric conversion efficiency(PCE)has increased from 3.8%in 2009 to 24.2%now,which is similar to the commercially-produced crystalline silicon solar cells.It is the most likely to replace crystalline silicon solar cells and become the main force of solar cells in the future.Perovskite materials are commonly used to prepare the absorbent layer of perovskite solar cells.The quality of the thin film is the decisive factor affecting the photoelectric performance of perovskite solar cells.Therefore,it has been a research focus to control the nucleation rate of crystals,slow down the film formation rate,and regulate the morphology of thin films to prepare devices with high quality films.Thin films with good film forming quality,fewer holes and high coverage can reduce the compound velocity of carriers,facilitate the extraction rate of carriers,and further improve the performance of devices.In this paper,additives are mainly used to improve the quality of the film morphology.Two different types of additives are developed to add to the perovskite light absorption layer to improve the film morphology,improve the film density and smoothness,and improve the photoelectric performance of perovskite solar cells.The main research results of this paper are summarized as follows:(1)Perovskite thin films were prepared by using 2,6-ditert-butyl-4-methylphenol(BHT)as additive,and the addition of this additive regulated the quality of perovskite thin films.The main mechanism is that hydroxyl group in BHT and iodide ion in perovskite form hydrogen bond to enhance the cohesion between adjacent perovskite crystals,and BHT is wrapped on the surface of perovskite to block the entry of water and oxygen.The prepared thin films have fewer holes,lower roughness and better coverage,and the carrier life is significantly increased after the addition of BHT,and the carrier recombination is also significantly reduced.The device structure used in this paper is FTO/c-TiO2/CH3NH3PbI3/Spiro-OMeTAD/Ag solar cell,and different concentrations of BHT are added into the precursor solution to prepare different perovskite solar cells.The results showed that when the photoelectric conversion efficiency of 4.2 wt%BHT the device was the best,and the filling factor(FF)was greatly improved(from 60.60%to 72.70%),the open circuit voltage(VOC)was 1.07 V,the short circuit current density(JSC)was 23.43 mA/cm2,and the PCE was improved from 14.93%to 18.28%.Therefore,this strategy can produce high quality perovskite thin films with smooth,dense and small roughness,so as to produce high and stable PCE of perovskite solar cells.(2)The quality of the perovskite absorber film directly determines the performance of the device.We added the additive potassium selenium-cyanate(KSeCN)into the precursor solution of perovskite,and the Pb(SeCN)42-complex intermediate generated before the decomposition of perovskite.It has strong binding force and inhibits the decomposition of perovskite.The unshared pair electrons of Se atom and N atom in SeCN-of the intermediate can interact strongly with Pb ion,which stabilizes the framework structure of perovskite and improves the quality of the perovskite film.The results show that by optimizing the different concentrations of KSeCN,we have prepared perovskite thin films with large grain size and dense and smooth quality.The PCE based on this device increased from 14.34%to 18.41%.More importantly,the carrier life of perovskite films without KSeCN was increased by 2.2 times,indicating that the films prepared with KSeCN had fewer defects and the carriers had a longer survival time.It is significant to improve the photoelectric performance of the device.In addition,compared with the devices prepared without KSeCN,the devices show better stability.After the unpackaged solar cells are placed in the air for 500 h,the PCE remains above 85.3%.In this paper,two different types of additives(BHT and KSeCN)are added to promote the homogeneous nucleation of perovskite and improve the quality of perovskite film,thus improving the PCE and stability of perovskite solar cells.