Study On The Effect Of Pre-heated Delay Annealing Process And Npb Doping On The Performance Of Perovskite Solar Cells

Since 2009,perovskite solar cells firstly have appeared in the world,they have been widely studied due to their tons of advantages such as low materials price,simple preparation process,and huge potential to fabricate large-area flexible devices.Until 2019,the highest power conversion efficiency(PCE)has reached 25.2%and the development speed is unmatched by other photovoltaic materials.The development of perovskite solar cells has a significant impact on the application and development of new energy.In order to improve the performance of devices,scientists around the world have came up with countless solutions and achieved excellent results.However,many basic intrinsic mechanisms are still need deeper understanding.The works mainly focus on the study of the crystallization kinetics of the perovskite absorber layer.Pre-heated delay annealing process and hole transporting layer modification were used to optimize the quality of perovskite crystallization,thereby improving the photovoltaic performance of the perovskite solar cells.The main contents of this thesis include the following two parts.1.Aiming at the study of crystal growth process of perovskite film(MAPb I_xCl_3-x),we demonstrated the importance of pre-heating treatment on perovskite nucleation and phase transition through controlled crystal growth dynamics,and we also investigated the effect of standing time after pre-heated treatment on MAPb I_xCl_3-xperovskite layer for the performance of PSCs.Combined the pre-heating treatment with fine-tuning the appropriate standing time,perovskite films with large crystal grains and homogeneous coverage were formed.Perovskite solar cells based on employing perovskite films treated with pre-heated delaying 1 hour to anneal achieved the PCE of 16.18%,which is significant improvement in PCE from12.35%as compared to the reference devices(prepared with the conventional gradient annealing process).It is found that the improvement in performance of PSCs with pre-heated delaying treatment is the direct effect of homogeneous nucleation by control the evaporation rate of solute and phase transition during pre-heated and standing process,which is beneficial for the formation of high quality perovskite absorber films.This study provides a new method to prepare large area perovskite solar cells with low cost.2.Hole transporting material poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)(PTAA)is currently widely used in perovskite solar cells,but it is mostly used in positive structures as its hydrophobicity.In order to improve its wettability,a?-conjugated small molecule N,N'-bis(naphthalen-1-yl)-N,N'+-bis(phenyl)benzidine(NPB)is introduced into PTAA hole transport layer in inverted perovskite solar cells(PSCs).The NPB doping induces better perovskite crystal growth owing to a strong?-?interaction with PTAA and cation-?interactions with CH₃NH₃⁺(MA⁺).In addition,NPB doping not only improves the wettability of PTAA and regulates the perovskite crystallization to achieve larger perovskite grain size,but also moves the valence band energy of the hole transport layer closer to the perovskite layer.Consequently,the fabricated inverted PSCs delivered a PCE of 20.15%,with a short-circuit current density(J_SC)of 22.60 m A/cm²and open-circuit voltage(V_OC)of 1.14 V.This outcome indicates that PTAA:NPB composite materials present great potential for fabricating high-performance PSCs.