Perovskite Crystallization And Interfacial Modification Of Carbon Electrodes In Mesoscopic Solar Cells

Organic-inorganic hybrid halide perovskite solar cells（PSCs）have achieved a recording power conversion efficiency（PCE）of 25.7%in the past few years,which is quite close to the PCE of single crystal silicon solar cells.Hole-conductor-free printable mesoscopic perovskite solar cell（p-MPSC）based on titanium dioxide/zirconium dioxide/carbon（mp-TiO₂/mp-ZrO₂/C）mesoscopic scaffold favors commercial scale production for its low cost,large-scale fabrication,and high stability.Compared with traditional PSC,p-MPSC suffers from severe open-circuit voltage(V_OC)loss,which restricts the p-MPSC performance.In this thesis,the perovskite/carbon interface modification is carried out to energy level alignment,enhancing the open-circuit voltage.The main contents are as follows:（1）Additive and annealing engineering are applied to optimize the Cs_0.05FA_0.95PbI₃-based p-MPSC device.The effect of methylammonium chloride（MACl）as an additive in enhancing the perovskite crystallization and promoting the perovskite phase is studied by grazing-in X-ray diffraction（GIXRD）test.After optimizing the precursor concentration and solvent annealing process,a best device with a PCE of 16.1%,an open-circuit voltage of 959 mV,a short-circuit current density of 22.5 m A·cm^-2,and a fill factor of 0.704 can be obtained.（2）Through controlling the stored humidity,theα-FAPbI₃ in the carbon layer could transform toδ-FAPbI₃ while the phase transition ofα-FAPbI₃ in the mp-TiO₂/mp-ZrO₂layers is suppressed due to the protection of mesoscopic scaffold.By analyzing the energy levels ofα-FAPbI₃ andδ-FAPbI₃,it is found thatδ-FAPbI₃ can be served as an electron blocking layer in the perovskite/carbon interface,which restrain the non-radiative recombination.After humidity treatment,the V_OCof the device is increased from 975 mV to 1020 mV,and the PCE is increased from 15.81%to 17.11%.（3）A low dimensional perovskite is constructed at the perovskite/carbon interface through cation insertion to assuage the mismatched energy level.When the device is soaked in phenethylammonium hydroiodide（PEAI）solution,perovskites in the carbon electrodes can be converted into low dimensional perovskites.In combination with the soaking experiment of lead methylammonium iodide（MAPbI₃）single crystal,it is speculated that the device exhibits a low dimensional perovskite structure with a gradient distribution of layers from the carbon electrode to the interior,and the gradient distribution structure is conducive to the transport of carriers.The average V_OCof the treated MAPbI₃perovskite device is increased from 920 mV to 990 mV.The device PCE is increased from15%to 16.26%.The interface modification is also performed in the Cs_0.05FA_0.95PbI₃device,and a device efficiency of 17.47%with a V_OC of 1023 mV could be obtained.（4）CsPbBr₃ nanocrystal is applied in the perovskite precursor to stabilize the formamidine perovskite.It is suggested that CsPbBr₃ could serve as the nucleation cite ofα-FAPbI₃ to ameliorate the perovskite crystallization.The incident photon-to-electron conversion efficiency（IPCE）spectra shows the CsPbBr₃ addition has little effect on the absorption cut-off edge ofα-FAPbI₃,indicating an enhanced phase purity.When the CsPbBr₃-stabilized device is treated with humidity,the V_OC can be increased to 1137 mV,which is comparable to that of the planar PSC.The device with an optimized composition of（FAPbI₃）_0.9（MAPbBr₃）_0.05（CsPbBr₃）_0.05 achieved a PCE of 17.53%and a V_OC of 1021mV.The unencapsulated device with CsPbBr₃ addition delivers an enhanced light-soaking stability in the continuous maximum power point tracking test under illumination,which shows negligible decay after 30 min illumination.