Study On The Effect And Mechanism Of Perovskite Crystal Growth And Morphology Control On Solar Cell Performance

Organic-inorganic perovskite and its derivatives as a new branch of solar cells have achieved rapid development since miyasaka and co-workers reported perovskite solar cells(PSCs)for the first time in 2009.In the past few years,PSCs have shown unexpectable and rapid progress in the field of solar cells due to the high power conversion efficiency(PCE)and relatively low cost.This certified record was refreshed up to 22.1%until today,reported by KRICT.As the core of the perovskite solar cell,the optical absorption layer has a crucial influence on the final performance of the device.During the preparation process,the existence of not continuous,complete coverage pore films which have the chaos growth direction,bad crystallization of perovskite crystals,many traps and internal defects,leading to low photocurrent and the fill factor as well as performance of perovskite cell.The crystal growth process and the morphology of the thin films are closely related to the preparation conditions,materials and environment.Optimization of thin film preparation process,regulation of perovskite crystal growth and morphology,improve the film coverage and uniformity,reduce the formation of internal defects in thin films,obtain continuous,no pinholes,full coverage films,flatness high quality perovskite crystal is very important for solar cell performance.In this thesis,we focus on the growth and morphology control of perovskite crystals to improve the efficiency and stability of perovskite cell.In order to prepare high quality perovskite,series research works were carried out as follows:(1)We first investigated the effect of perovskite capping layer crystal morphology.We changed the volume of weak corrosive mixed anti-solvent to precisely control the capping layer thickness.At the same time,ultra-dry gas flow was used for protecting perovskite film as well as inducing the formation of low defects perovskite crystal grain.The device performance is greatly enhanced by shaping PCL with suitable thickness and good crystallinity grain.This was an easy and highly reproducible method for preparing devices with careful and precise control.Finally,we boosted the device PCE from 8.97%to 18.25%with the fill factor as high as 80.91%.An average efficiency peak of 17.57%for the champion cell was got with the PCL thickness around 240nm and good quality crystal grain.(2)preparation of large perovskite crystal with low internal defects,we demonstrated a fast preparation method for PSCs with nnealing temperature as high as 220? for the one-step deposition,and the film will be shaped in 15 s based on the precursor compositions of(FAPbI3)0.85(MAPbBr3)0.15 precursor compositions.The best device with a PCE of 17.1%has been obtained prepared at 220? and the average PCE of 16.6%with Jsc of 21.16mA/cm2,Voc of 1.05 V,and FF of 75.0%.(3)Perovskite surface morphology control.We developed an effective way to solve the problem of film cracking.By regulating ambient environment temperature during perovskite spin-coating process,film cracking can be effectively suppressed and restore the mirror-like surface.The power conversion efficiency was boosted from 13%to values more than 18%.(4)For making ultra-flat surface morphology,we have invented a brand new method based on the conventional solvent engeerning method of anti solvent,and found a highly reproducible method to control the growth of perovskite crystal:the spraying anti-solvent process(SAP).We report highly reproducible method for controlling perovskite crystal growth by SAP.When the anti-solvent landed on the substrate,atomized solvent particles can be evenly dispersed and contacted with film more softly and uniformly which can reduce the waves and eliminate ring defects of the perovskite film caused by impact and centrifugal force.After optimizing spraying operating conditions,the power conversion efficiency was boosted from 15.34%to 18.78%.Devices based on FA0.81MA0.15Cs0.025PbI2.5Br0.45 light absorber got a record PCE of 19.21%with high FF of 80.84%.(5)The preparation of the layered perovskite crystal to improve the stability by changing the stacking of crystals.This layered perovsikte combines features of high performance and stability,which originated from 3D and 2D type perovskite respectively.We have successfully fabricated solar cells based on[CF3CH2NH2]2(FA0.825MA0.15 Cs0.025)29Pb30(I0.85Br0.15)9i thin films,offering broader absorption and the possibility to achieve higher photocurrent.The best device with a PCE of 18.17%has been obtained in this mixed dimensionality perovskite system.Moreover,due to hydrophobic trifluoroethylamine chain and layer upon layer structure act as an impermeable barrier,the multilayered perovskite showed excellent property of moisture-resistant compared to their 3D perovskite.Through the above perovskite crystal morphology control,crack inhibition and layered perovskite crystal preparation,we can prepare smooth and high coverage of thin film under different atmosphere,and got stable and efficient solar cells.