Preparation Of FeS₂ And CoFe₂O₄ Nanocrystals And Application In Perovskite Solar Cells

Perovskite solar cells?PSCs?have achieved the highest power conversion efficiency?PCE?of 25.2%within the last few years,which is unparalleled in photovoltaic research.Apart from high efficiency,the device stability is another important issue needed to be solved for the future commercialization.The 2,2,7,7-tetrakis?N,N-p-dimethoxy-phenylamino?-9,9-spirobi fluorene?Spiro-OMeTAD?is the most commonly used hole-transporter for preparing high efficient PSCs,yet the indispensable dopants of corrosive 4-tert-butyl pyridine?TBP?and hygroscopic lithium-bis?trifluoromethane?sulfonimide?Li-TFSI?generally lead to poor device stability.What's more,the price of Spiro-OMeTAD hole-transporter is very expensive,nearly ten times higher than that of gold or platinum due to the complicated synthesis and purification,which greatly increases the production costs of PSCs.Therefore,the finding of new hole-transporters,especially dopant-free materials,becomes a research hotspot.Moreover,the solution process of polycrystalline perovskite membrane showed a high density of trap.These defects mainly exist in the polycrystalline perovskite membrane surface of the grain boundary and will lead to interface charge composite limiting device performance,by accelerating the degradation of perovskite membrane,leading to poor long-term stability.The defect passivation is ideal method to obtain efficient and stable PSCs.This paper focuses on the application of composite hole material interface engineering in perovskite batteries.The main research contents and results are as follows:?1?ODA-FeS₂ NPs are synthesized by thermal injection method and FeS₂+Spiro-OMeTAD hybrid HTL is prepared for PSCs.The UPS test shows that FeS₂+Spiro-OMeTAD guide belt is moved up,which is more matching with perovskite and conducives to the faster extraction of charges.Contact Angle measurment shows that FeS₂+Spiro-OMeTAD HTL film is more hydrophobic,which plays as a role of moisture-proof layer in PSCs and protects the perovskite layer.Tests of PL,TRPL and dark I-V indicate that FeS₂+Spiro-OMeTAD has better conductivity,faster hole extraction rate and lower trap density.The PSCs based on FeS₂+Spiro-OMeTAD have better photoelectric performance,the highest PCE is 19.48%,compared with 18.01%in the blank group,and the hysteresis effect is significantly improved.Under the bias voltage of 0.91 V corresponding to Pmax,the optimized PSCs can obtain the stabilized current of 20.81 mA cm^-2 and the stabilized PCE of 18.94%.?2?CoFe₂O₄ nanocrystal particles are synthesized by two-phase solvent-thermal synthesis.The chemical valence state composition of Co and Fe in CoFe₂O₄ can be seen by XPS test.The contact angle test shows that the modified perovskite film is more hydrophobic and the stability of PSCs is better.Tests on the defect state of PL TRPL shows that the modified perovskite film has a faster hole extraction rate and a lower trap density at the interface.The PCE value of the optimized device is up to19.65%,and the open circuit voltage(V_OC)and filling factor?FF?are significantly improved.Under the bias voltage of 0.94 V corresponding to Pmax,the optimized PSCs can obtain the stabilized current of 20.16 mA cm^-2 and the stabilized PCE of 18.97%.?3?CoFe₂O₄-Spiro-OMeTAD composite HTL is prepared for high efficiency and stable PSCs.The tests of PL and TRPL show that CoFe₂O₄-Spiro compound HTL has faster hole extraction rate.AFM test shows that the doping can make the HTL surface smoother,which is conducive to the improvement of filling factor and the better performance of the device.Electrochemical impedance test shows that the doping of CoFe₂O₄ can effectively inhibit the non-radiation recombination,leading to the highest PCE of 20.16%.