Planar Perovskite Solar Cells:Active Layer Optimization,Interface Modification And Fabrication Technology

In the past decade,the certified power conversion efficiency（PCE）of perovskite solar cells（PSCs）has rapidly increased from 3.8%to 25.7%,which has attracted widespread attention from academe and industrial circles.As an emerging clean energy technology,PSCs occupy a dominant position in the field of third generation photovoltaic power generation technology,contributing to the carbon peak and carbon neutral strategy.However,poor long-term stability and potential environmental pollution still hinder the commercial application of PSCs.Aiming at the vacancy defects,ion migration and lead toxicity of planar PSCs,we successfully achieve the preparation of low defect state density,phase-stable and lead-immobilzed perovskite films by virtue of defect passivation,surface modification and internal package strategy,thus enhancing the photovoltaic performance of PSCs.The detailed research contents are as follows:（1）A facile and broadly applicable surface modification strategy was developed to modulate the composition of the top of perovskite films.By applying Cd Br₂ to the perovskite films surface,the halide vacancies were filled and the uncoordinated Pb defects were passivated.Cd Br₂ surface modification strategy is found to be able to prolong carrier lifetime,decrease defect amount together with improve film quality of the typical compositional perovskites i.e.MAPb I₃,Cs_0.15FA_0.85Pb I₃ and Cs Pb I₂Br.As a result,the Cd Br₂-modified C-PSCs with the architecture of ITO/Sn O₂/MAPb I₃/C achieve a high efficiency of16.05%as well as promoted ambient,photo and thermal stability.（2）A kind of crown ether molecules with both electronegative cavity and negatively chargedπbond,DB18C6 was introduced to fabricate cation-immobilized and phase-stable FACs Pb I₃ photo absorbing layer.Benefiting from the crown ether electronegative cavity-cation complexation and electron-richπ-cation interaction,the photo-induced cation migration in FACs Pb I₃ film is inhibited to a large extent,achieving the preparation of phase-stable perovskite film.DB18C6-modified FACs Pb I₃ film shows excellent phase stability and remarkably negligible degradation even after 24 h continuous light-soaking.As a result,DB18C6-modified PSCs with the architecture of ITO/Sn O₂/FACs Pb I₃/spiro-OMe TAD/Ag achieve an enhanced PCE exceeding20.84%,retaining up to 94.73%and 90.18%of their original PCEs even after500 h continuous full sunlight light-soaking and 85℃ heating,respectively.（3）An in-situ polymerization self-shield strategy was developed to fix Pb²⁺in perovskite films in order to mitigate the Pb leakage of PSCs.Specifically,DMI monomers was introduced to perovskite precursor.During the thermal annealing process,the in-situ polymerization process occurred in perovskite film and thus formed perovskite-polymer hybrids.PDMI gathered at perovskite grain boundary can effectively inhibit the decomposition of perovskite film from the grain boundary,thus decreasing the sites of lead leakage.The interaction between C=O bond in PDMI and uncoordinated Pb²⁺has the capability of decreasing the defect state density of perovskite film and inhibiting the escaping of Pb²⁺ions.The Pb leakage amount is decreased to<2 ppm when unencapsulated devices modified by PDMI soaked in deionized water for 180min.The PSC devices based on in-situ polymerization self-shield strategy achieve a PCE of 20.67%.The PSC devices without external encapsulation retain up to 94.17%of original PCE after 1000 h storage in ambient conditions,superior to the control devices（81.72%）.（4）Phosphatidylcholine（PC）insulation layer was introduced to encapsulate perovskite active layer surface in order to inhibit the Pb leakage and decrease defect state density.When PC molecules with one end of hydrophilic and one end of hydrophobic interact with perovskite film,the phosphate group at the hydrophilic end and C=O bond as the electron donor both have interaction with Pb²⁺ions in perovskite lattice,realizing the inhibition of lead leakage.Meanwhile,the hydrophobic end is exposed,which can enhance the hydrophobicity of perovskite film.Benefiting from the enhanced hydrophobicity of perovskite film and the interaction between PC and Pb²⁺,the PSCs without any external encapsulation realizes over 90%Pb leakage amount inhibition when soaked in water.The PSCs with PC layer achieved 22.67%PCE.After stored for 2000 hours under environmental conditions（T=15±5℃,RH=30-40%）,the device can still maintain 92.62% of its initial PCE.