Investigation Of The Small Organic Hole Transporting Materials And The CsPbI₃ Inorganic Perovskite In Perovskite Solar Cells

Perovskite solar cells(PSCs)have attracted tremendous attention due to their excellent photo-electrical properties.The PSC device can be divided into three parts,which are electron transporting layer,perovskite layer and hole transporting layer.Wherein,the hole transporting layer plays a role in extracting the photo-generated holes from the perovskite layer,which will facilitate resisting the recombination of the holes and electrons.Perovskite layer is the key component in the PSC device,which can convert the photon into electron.As a result,developing novel and efficient hole transporting material and perovskite material are of great significance to the development of the PSCs.The study of the structure of Spiro-OMeTAD can help designing new hole transporting materials.This peculiar "Spiro" configuration is regarded to be a main reason for its superior electrical properties.At the same time,many hole transporting materials have been successfully proposed based on this synthesis strategy.However,researches about the "di-Spiro”configuration are still relatively sluggish.In the second chapter,we have probed the properties of a new hole transporting material based on "di-Spiro" configuration for the first time.It has been found that this "di-Spiro" structure endows the molecule with a higher isotropy,which will assist holes "hopping" from different directions.As a result,a higher hole mobility of 9.07×10-4 cm2 V-1 s-1 and power conversion efficiency of 17.4%have be obtained.Indolo[3,2-b]carbazole is a planar conjugated aromatic ring,and it possesses a very strong inter-molecular π-π-interaction,which is in favor of forming the charge transporting tunnel.Nevertheless,too strong molecular interactions will result in severe inter-molecular aggregations,which can lower the film-forming ability of the material consequently.In the third chapter,we have modified the level of molecular interactions by changing different functional groups on indolo[3,2-b]carbazole.Thus,the hole transporting material with a high hole mobility of 1.5 × 10-4 cm2 V-1 s-1 as well as a good film-forming ability based on indolo[3,2-b]carbazole has been obtained.The as-prepared dopant-free hole transporting material possesses a higher anti-moisture ability,which can act as a better protective layer.In addition,the facile synthesis route without using any expensive catalysts makes it a cheap material,which gives a PCE of 17.7%.Organic-inorganic hybrid perovskite suffers the thermal instability problem due to the volatile properties of the organic components under the thermal stress.Substituting the organic components occupied at the corner sites of the[PbI6]2-octahedral with the Cs+,the CsPbI3 inorganic perovskite is thought to be a promising alternative for its improved thermal stability.In the fourth chapter,we have studied the properties of the CsPbI3 inorganic perovskite solar cells.It has been found that the so-called "HPbI3" crystal synthesized through the anti-solvent vapor method is DMAPbI3.Moreover,the content of DMAI in the CsPbI3 perovskite will decrease as the annealing temperature and time increase.In addition,a reversible "light soaking effect" has been found in the as-prepared CsPbI3 perovskite solar cells.The PCE increases from the 10.8%to 18.3%after 180 s light soaking.It is suggested that the stronger built-in field and a decreased trap density of the device after the light soaking may play a major role in this effect.