Elevating Stability Of CsPbI₃ Inorganic Perovskite Films And Device Investigation

Perovskite solar cells,as for the simplified manufacturing process and increasing industrial demand,are now treated as the pioneer for the next generation among photovoltaic devices.Indeed,the quality of the absorber layer has decisive impact on the performance of corresponding photovoltaics.Due to the existence of organic molecule in organic-inorganic hybrid perovskite films,those films will unavoidably go through the process of degradation,which causing the dis-function of devices.The researchers tried to walk out the dilemma by substituting the A-site in the structure of ABX3 with inorganic element cesium(Cs),this helps to prolong thermal stability and maintain perovskite phase.Known for its long diffusion distance of carriers and suitable bandgap,researches focused on CsPbI3 are plentiful.However,the application of all-inorganic devices is usually limited by the spontaneous phase transition of CsPbI3 and mismatch of energy alignment,causing the limitation on the photovoltaic performance.Targeting on defects existed either upon the surface or inside the bulk of perovskite films,strategies based on the crystallization process are sequentially proposed.To shape suitable surface contact for devices and to mediate the crystallization through both intermediate phase and precursor can effectively amplify the quality of CsPbI3 perovskite films,that can pave the road for improvement on transport ability of carriers and the photovoltaic outcome.The main research contents can be assembled as followed:(1)Unwanted phase transfer of CsPbI3 perovskite caused by defects upon surface can hinder the photovoltaic performance.Surface engineering targeting on those defects is carried out.1H,1H-Perfluorooctylammonium Iodide(PFOAI),combining the long carbon chain with hydrophobic functional group(-CF),was introduced and effectively played the role of defending the water in the air and mending the defects upon the surface of perovskite films.The long carbon chain with fluorine in PFOAI avoided the phase transfer as for its high hydrophobicity,which made the high-quality perovskite films possible.On the other side,the strengthened Pb-I-Pb framework of CsPbI3 brought by the interaction with PFOAI stabilized the perovskite phase and decreased the trap density.This method brought improvements from different aspects,include but not limited on morphology,optical properties and photoelectric properties of the perovskite films.Eventually,the pin-hole free and uniformed perovskite films can be obtained,the best PCE of PFOAI-CsPbI3 can reach 18.24%.(2)Based on the surface engineering,the improvements are usually limited on the surface but hard to deep inside the bulk of perovskite films.In this way,the method of intervening the intermediate phase to indirectly adjust the nucleation of perovskite(named as Intermediate-phase-modified crystallization,IPMC)was successfully introduced.Acting as the adjustment of intermediate phase,Pyrrolidine Hydriodide(PI)was introduced through spin-coating before the nucleation of DMAPbI3 phase.Combining the results gained from NMR and FTIR,it’s conformed that the hydrogen bond built between PI and DMAI changed the electron cloud density and amplified the chemical environment for nucleation of perovskite phase during the first stage,which provided support for the formation of a stable perovskite structure in the second stage.Besides,PI inside the CsPbI3 films cleaned the blocks for charge carriers,leading to the high carriers lifetime and suitable energy bandgap alignments.PSCs based on PICsPbI3 achieved a PCE of 18.72%with superior thermal stability.(3)Intervening the nucleation of intermediate phase at the first annealing statement could lower the defects inside perovskite films,the effect was realized through adjusting the chemical statement of DMAPbI3.In this work,the 2-AET(2Aminoethanethiol Iodide)was introduced as addictive to assist the nucleation,which devoted to build stable perovskite structure.Through comparing the two methods(surface passivation and addictive),the 2-AET doped CsPbI3 perovskite films indeed showed improved quality.After combining the outcome of film morphology with photoactive properties,it’s confirmed that the Pb-I-Pb framework is reinforced.That is attributed to the improved crystallization and uniformed grain arrangement,which facilitating the carriers concentration.As a result,the apparently improvement in humidity-resistance can be achieved for the existence of-SH bond inner the 2-AET.(4)Compared with indirect adjustment to the nucleation process,the precursor optimization might also be clever recipe,due to the direct influence on the perovskite nucleation.In this work,we directly introduced the Piperazine Dihydriodide(PDI2)and 1,4-Phenylenediamine Dihydroiodide(PDAI2)into precursor and made it participated in the whole crystallization of inorganic CsPbI3 perovskite films.After precisely adjusting the ratio of the components(CsI,DMAI,PbI2 and PDI2/PDAI2)inside the precursor,the construction of low-dimensional phases could be achieved,and the successful fabrication of thermal-stable and humidity-stable inorganic perovskite films can eventually be realized.After comparison,films based on the PDI2 showed flattened and regularized morphology.Besides,those films are capable of high humidity resistance and thermal-stability,which prompt the superior stability of devices.Investigations in this thesis are focused on the manufacture process and nucleation mechanism of all-inorganic perovskite materials.Systematically exploration concerning about different statement of crystallization had been carried out,strategies aiming for decreasing the defects had been proposed.Based on that,the relevant solutions are proposed and high-quality perovskite films can be obtained.In this way,the issues concerning stability and defects are primarily solved,which lay the basement for the industry application.