Effect Of Benzotriazole Derivatives On Optoelectronic Properties And Stability Of Perovskite Films

In the third generation of new photovoltaic devices,halide perovskite solar cells（PSCs）have been evaluated as the most competitive and promising photovoltaic technology.Perovskite semiconductors have engaged extensive attention on account of their distinct crystallographic structure and remarkable physical and chemical properties,such as low exciton binding energy,high defect tolerance and fast carrier mobility.The deposition of high-quality perovskite thin films with uniform and controllable morphology is the key to the realization of efficient and stable PSCs.At present,there are a lot of trap defects in polycrystalline perovskite films,which will induce nonradiative recombination,and thus decrease the open-circuit voltage and accelerate the degradation of perovskite films under light,humidity and other operational conditions.Suppressing the nonradiative recombination in perovskite active layer is highly desired to boost the power conversion efficiency（PCE）and operational stability of PSCs.In this thesis,high-quality perovskite thin films were prepared by feasible additive engineering with benzotriazole derivatives to reduce the defect sites in the films and inhibit nonradiative recombination.A variety of characterization approaches were utilized to characterize the performances of perovskite films and devices,and further explore its influence on the PCE and stability of PSCs.（1）A benzotriazole derivative（6-chloro-1-hydroxybenzotriazole,Cl-HOBT）is applied to modify methylammonium lead iodide（MAPb I₃）perovskite film.It is revealed that the incorporation of Cl-HOBT could improve the crystallinity of perovskite crystal and reduce the trap density by about 20%.Meanwhile,Cl-HOBT elongated the photoluminescence carrier lifetime and charge-recombination lifetime,implying the trap-assisted nonradiative recombination is greatly suppressed.Besides,the improved energy level alignment and enhanced built-in potential are conducive to the charge carrier separation and transfer process with Cl-HOBT.Consequently,the inverted MAPb I₃ PSCs acquire a PCE of 20.27%and an open-circuit voltage(V_oc)of 1.09 V,along with an 85%sustaining of the initial PCE under stored at relative humidity of 20%for 500 h.Significantly,the existence of Cl-HOBT could inhibit the formation of Pb⁰ defect under prolonged UV illumination to retard the degradation of perovskite film.（2）Benzotriazole（BTA）,5-chlorobenzotriazole（Cl-BTA）and 1-hydroxybenzotriazole（HOBT）were applied to reveal the influence of different functional groups on the properties of perovskite films.The results demonstrate that the three additives are capable to enhance the PCE of PSCs,with different effects on the photovoltaic parameters.The introduction of BTA is beneficial to the increase of V_oc of PSC,the substitution of Cl is more conducive to the enhancement of current density(J_sc),and the substitution of hydroxyl make for the increase of both V_oc and J_sc.The performance improvement is mainly ascribed to the optimization of carrier extraction and transfer efficiency,the reduction of defect sites and the effective inhibition of nonradiative recombination.The PSC device with HOBT achieved a PCE of 19.80%and excellent charge extraction efficiency of 90%.Therefore,high-quality perovskite films were successfully fabricated by incorporating new benzotriazole additives into perovskite precursor,which effectively reduced the nonradiative recombination loss,and the functional mechanisms of additives are summarized.It is believed that this study paves a novel path for the realization of high-efficiency PSCs with UV-stability.