Studies On Perovskite Solar Cells With TiO₂ Electron Transport Layer

Perovskite solar cells（PSCs）have been attracting extensive attention and the performance has been encouraging with great leaps,in the past decade.However,the detailed working principles of PSCs remain to be further studied and proved.The commercial application of them still can not be available soon.The work in this dissertation is focused on the perovskite solar cells with structure of ITO/TiO₂/MAPbI₃/spiro-OMeTAD/MoO₃/Ag and the fabrication of perovskite film without anti-solvent.The investigation on the phenomena observed in the test of the PSC devices has been launched,which could lead us to learn more about PSCs.1 Ligand-free rutile TiO₂ nanoparticles were synthesized and applicated to PSCs as electron transport layer.During the transient photovoltage measurement on the device,an overshoot phenomenon of open-circuit voltage(V_oc)was observed when the illumination was switched off.The evolution of the overshoot was investigated along with different conditions.Based on the results,a model was set up to explain the origin of overshoot.It originated from the band bending at the interfaces caused by ionic migration and accumulation,which resulted in reverse motion of carriers.The carriers’reverse motion formed a local electric field,which went against the built-in field.When the illumination was switched off,the disappearance of the local electric field resulted in the overshoot.2 The capacitance of PSC device,which was applied large forward bias,turned negative in the low frequency（under 1 kHz）region,when capacitance-frequency（C-F）measurement was carried out in dark.Based on the results of measurement on the capacitance of PSC devices with PCBM as modification layer,one knew that the negative capacitance（NC）effect could be reduced by illumination and the PCBM passivation of interface.A model of interfacial transport was established to explain the origin and the suppression of NC effect.The NC effect in PSCs originated from the electron trapping/detrapping caused by the interfacial defects.The interfacial defects decreased via the carrier filling and the passivation of PCBM,which led to a suppressed NC effect.3 Gas-assisted deposition（GAD）was applicated in fabrication of perovskite films,the solvent engineering was introduced as well.A high-quality film with single-layer crystal structure in the vertical direction was gained.Based on the film,PSC devices with average PCE of 16.50%were obtained.Through the characterization and the comparison of the device performance with devices made by two-step method and one-step method,we could conclude that the GAD method could substitute the two other methods completely.GAD is a better method with easier operation,lower cost,and environment amity.We also characterized the fabricated PSC at low temperature,finding that ionic migration was a significant reason for hysteresis.