Study On Interface Passivation And Photoelectric Characteristics Of MAPbI₃ Perovskite Solar Cells

In this paper,in order to improve the power conversion efficiencies（PCEs）of perovskite solar cells（PSCs）,it is necessary to passivation of trap states in grain boundaries（GBs）and reduce carrier recombination both in the bulk perovskite films and interfaces.Thus,we incorporated polycaprolactone（PCL）agent into perovskite precursors and acetonitrile（ACN）in the Spiro-OMe TAD precursor,respectively.The micromorphology,crystal structure and binding energy of elements were characterized by SEM（scanning electron microscope）,XRD（X-Ray Diffraction）and XPS（X-Ray photoemission spectroscopy）,respectively.So as to exlain the mechanism of the improvement of additive on the performance and stability of the devices,the defect density and carrier recombination process was systematacially studied by dark J-V curves,impedance spectroscopy and photoluminescence（PL）etc.The main studying contents of this paper are as follows:（1）The influence of PCL additive on on the performance of the PSCs and the mechanism on carrier recombination dynamics.Varied concentration of PCL agent was introduced into perovskite precursors to study the influence of PCL additive on on the performance and stability of the devices.The corresponding best performance device added with 0.30 wt%PCL agent generates a conversion efficiency of 19.78%,26.6%higher than that of the pristine device and retains～88%of the initial values after 21 days’storage without any encapsulation in ambient air.The new polar polymer agent PCL can play a bifunctional role in defect passivation of perovskite interface.For one thing,carbonyl（C=O）chain as Lewis base ligand can passivation of the Pb²⁺and other cation defects at the GBs via the donor of electron.For another,the emptyπ-conjugated polymer PCL can promote the formation of electron acceptor,namely Lewis acid,leading to passivation of the trap states due to the migration of I^-ions across the interface or GBs.（2）The influence of ACN additive on on the performance and hysteresis of the PSCs.Varied concentration of ACN additive was introduced into Spiro OMe TAD precursor to study the influence of ACN additive on on the performance and hysteresis of the devices.The corresponding best performance device added with 15%ACN additive in chlorobenzene generates a conversion efficiency of 17.89%,11.4%higher than that of the pristine device（16.06%）.The hysteresis index（HI）decreased to 0.18,51.4%lower than that of the pristine device（0.37）.For one thing,this small amount of ACN can dissolve impurities in the surface of the perovskite layer.For another,ACN additive can promote the formation of an interdiffusion structure between perovskite and Spiro-OMe TAD layers,which leads to an improved electrical contact,and reduces recombination losses at the interface between the perovskite and Spiro-OMe TAD layers and,consequently,enhances the V_oc（open-circuit voltage）of the devices.However,the excess amount of ACN additive can result in the thinned perovskite layer and thicken Spiro-OMe TAD layer due to the corrosive effect of ACN additive on perovskite layer,leading to performance degradation of the devices.（3）The influence of reaction time between ACN additive and perovskite layer on the performance of the PSCs.Based on the study in previous chapter,the influence of reaction time between ACN additive and perovskite layer on the performance of the PSCs was explored indetail.At the optimized concentration of 15%ACN additive in chlorobenzene,the solubility of ACN additive in chlorobenzene decreases with the prolonging of reaction time.As the reaction time of ACN additive ranges from 0～15s,the modification and passivation effect on perovskite interface improve linearly with the reaction time.Wheras the reaction time of ACN additive is more than 15s,the modification and passivation effect on perovskite interface remain unchanged.The champion PCE of the devices based on the 0 s、5 s、15 s and 30 s reaction time of ACN additive are 16.35%、17.28%、17.84%and 17.70%,respectively,attributed to the significant enhancement of photovoltaic parameters such as V_ocand FF.