Molecular Engineering Of Perylenediimide-based Electron Transport Materials And Their Applications In Perovskite Solar Cells

As the crucial functional material of an inverted planar PSC,the electron transport material(ETM)plays an important role in electron extraction and transport,further inhibiting the charge recombination.So far,the most commonly used ETMs for highly efficient inverted planar PSC are fullerene derivatives(C₆₀,PC₆₁BM,PC₇₁BM,and ICBA),which exhibit high electron mobility and isotropic electron transfer properties.However,the draw-backs of fullerene-based ETMs,such as high cost,instability,and limited tunability of energy level,limit their commercial application in the future.Therefore,it is highly desirable to develop novel highly efficient ETMs as alternatives.In principle,to functionalize as efficient ETMs,suitable energy levels,excellent electron extraction and transport properties,good film-forming property,and easy synthesis routes are basically required.Recently,researches manifest the photovoltaic performance of newly developed ETMs intimately associated with their molecular spatial structures.Hence,scientific and reasonable molecular structure engineering is crucial for building up a highly efficient non-fullerene small molecular ETM.The mainly studies of this thesis is the design and synthes of novel organic small molecule ETMs in inverted planar PSCs.In this thesis,the relationship between the molecular spatial configuration and their optoelectronic and photovoltaic properties are systematically investigated.The specific contents are as follows:1.To restrict the aggregation and further enhance the photovoltaic performance of perylenediimide(PDI)-type ETMs,two PDI-based ETMs,termed PDO-PDI2(dimer)and PDO-PDI3(trimer),were constructed by introducing a phenothiazine 5,5-dioxide(PDO)core building block.The research manifests that the optoelectronic properties and film formation property of PDO-PDI2 and PDO-PDI3 were deeply affected by the molecular spatial configuration.Applied in PSCs,PDO-PDI3 with three-dimensional spiral molecular structure,exhibits superior electron extraction and transport properties,further achieving the best PCE of 18.72%and maintaining 93%of its initial efficiency after 720 h aging test under ambient conditions.2.By selecting the torsion structure of snail[fluoren-9,9'-xanthene](SFX)as the core,and using molecular engineering methods,the introduction of pyridine group in SFX and the linkage of PDI on fluorene core,a bifunctional electron transport material SFX-Py-PDI2 was designed and synthesized.The results mainfests that the bare pyridine can effectively reduce the defects on the perovskite surface and grain boundary,improved the crystal quality of perovskite,and inhibited the non-radiative recombination at the perovskite/electron transport layer interface.Moreover,when SFX-Py-PDI2 doped into the perovskite solar cell,the photoelectric conversion efficiency achieved 20.5%.3.A highly efficient all-inorganic PSC with CsPbI₂Br as light absorption material is assembled by employing a binary electron transport layer(ETL),which consists of PC₆₁BM and a newly designed non-fullerene electron transport material SFX-PDI2.The formed binary system primely implements in the form of a thin,uniform and full coverage ETL,and possesses more excellent electron extraction and transport properties than both pristine PC₆₁BM and pristine SFX-PDI2.As a result,the binary ETL based PSC with CsPbI₂Br as light harvesting material achieved an efficiency as high as 15.12%,which is among the highest performance for inverted planar structured all-inorganic PSC.