Research On Performance Improvement Of Perovskite Optoelectronic Devices Based On Surface Passivation

In recent years,our country’s power energy problems have become increasingly prominent.Perovskite materials,a new generation of semiconductor materials,have become the most promising candidate materials in photovoltaic and luminescence fields due to their inherent photoelectric characteristics,such as high absorption coefficient,adjustable band gap,long carrier lifetime and long carrier diffusion length.However,the performance and stability of perovskite solar cells（PSCs）and perovskite white light-emitting diodes（WLED）are still the biggest bottleneck restricting their further developments,the performance and stability of the device are mainly related to the defect sites of the perovskite material.In this paper,the surface passivation and encapsulation of the perovskite materials are used to improve the perovskite films quality and photoelectric characteristic,and the application of perovskite materials in solar cells and LED devices is carried out.The conclusions are as follows:（1）The surface of the perovskite was passivated by adding trioctylphosphine oxide（TOPO）chlorobenzene solution while spin-coating the MAPb I₃ perovskite layer.TOPO ligands were adsorbed on the MAPb I₃ perovskite surface via the binding of O atom in—P=O bond with the uncoordinated Pb.After introducing TOPO,the crystal structure and band gap（E_g）of the perovskite films was not changed,but the PL intensity and PL lifetime were significantly enhanced.Finally,an inverted structure PSCs was prepared.The power conversion efficiency（PCE）of the TOPO passivated PSCs was increased from 10.84%to 14.24%.At the same time,the stability of TOPO-modified PSCs at room temperature without encapsulation is greatly improved.（2）The cesium trifluoroacetate（Cs TFA）was used to replace the traditional Cs I to prepare Cs/FA/MA perovskite films.The perovskite films doped with 5%Cs TFA shows a larger grain size,fewer holes and larger E_g of 1.611 e V.Then,the effects of different spin-coating speeds from 4000 rpm to 7000 rpm on the morphology of Cs/FA/MA perovskite films and performance of the PSCs device are studied.At 6000rpm,the Cs/FA/MA perovskite films quality is the best,there are no holes on the surface and the PCE of the device is the highest.Afterwards,the MACl post-processing strategy was used to passivate the surface of the perovskite films.Finally,at 6000 rpm perovskite layer spin-coating speed and 5%Cs TFA doped Cs/FA/MA perovskite films which added MACl post-processing as the light-absorbing layer,an inverted structure PSCs was prepared,and the PCE of the PSCs devices reached 12.19%.（3）The DDAB-Cs PbX₃ QDs and SiO₂ wrapped DDAB-Cs Pb X₃ QDs were prepared via ligand exchange and tetramethoxysilane（TMOS）hydrolysis encapsulation strategy.The shorter chain ligand DDAB replaced the OA and OLA ligands and attached to the surface of Cs Pb X₃ QDs.The cation of DDA⁺can strongly bind to the QDs surface and efficiently passivate the surface defects,which leads to a narrow FWHM and high PLQY.In addition,the stability of Si O₂ coated DDAB-Cs Pb Br₃ QDs has been significantly improved,which is attributed to the Si O₂protection.Finally,WLEDs are made by mixing green DDAB-Cs Pb Br₃@Si O₂ QDs and red DDAB-Cs Pb Br₁I₂@Si O₂ QDs phosphors on a commercial blue Ga N chip.A high-quality WLED with strong white light emission and good EL stability for continuous-time work was obtained.