Research On Interface Modification And Spectral Regulation Of Perovskite Solar Cells Based On N-i-p Structure

Organic-inorganic hybrid perovskite materials have attracted much attention due to their suitable optoelectronic properties.Up to now,the laboratory certification efficiency of perovskite solar cells（PSCs）prepared using organic-inorganic hybrid perovskite materials has reached 25.7%,which is very close to the level of silicon solar cells.However,it is still far below the theoretical limit efficiency,so if PSCs want to become a new generation of commercial photovoltaic devices,there are still many problems to be solved,for example,there is still a lot of room for improvement in efficiency,and there are a large number of oxygen vacancy defects at the electron transport layer（ETL）/perovskite interface,the non-radiative recombination at the interface caused by the large energy barrier between ETL and perovskite,defects at the grain boundary and interface of the perovskite films,the unbalanced charge-carrier transport between the perovskite-transport layer interface,mismatch between perovskite absorption spectrum and solar spectrum and the poor UV stability seriously hinder the efficiency and stability of PSCs.To further solve the above-mentioned problems,we introduce organic semiconductors,inorganic semiconductors,vitamin natural molecules that exist in nature into PSCs to achieve interface engineering modification and fluorescent down-conversion materials into PSCs to achieve spectral regulation,and finally greatly improve the efficiency and stability of PSCs.The following is the specific research content:（1）Firstly,a versatile bottom-up bilayer interface modulation strategy was developed to passivate the ETL and ETL/perovskite interface by incorporating 2,2′-[[12,13-Bis（2-butyloctyl）-12,13-dihydro-3,9-dinonylbisthieno[2’’,3’’:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-e:2′,3′-g][2,1,3]benzothiadiazole-2,10-diyl]bis[methylidyne（5,6-chloro-3-oxo-1 H-indene-2,1（3H）-diylidene）]]bis[propanedinitrile]（BTP-e C9）into the SnO₂/perovskite interface.BTP-e C9 has good electron transport ability,high carrier mobility,high structural flexibility and good film formation properties.BTP-e C9 can effectively prevent holes from reaching FTO through pinholes and cracks of SnO₂,thereby promoting charge extraction and hindering the electron-hole recombination process at the heterointerface.In addition,BTP-e C9 with a suitable conduction band can accelerate the extraction and transport of electrons from perovskite to ETL with better electron transport capability.BTP-e C9 can sequentially passivate active Sn ions in SnO₂,as well as bulk defects and ion vacancies defects of perovskite thin films through a bottom-up passivation process.This interface engineering modification strategy simultaneously realizes the modulation of the interfacial energy band alignment,the passivation of interfacial defects,and the regulation of perovskite crystallization,thereby improving the device performance,and significantly suppressing the hysteresis phenomenon.As a result,the two-step PSCs achieved a power conversion efficiency（PCE）as high as 23.10%,and the one-step PSCs achieved a champion PCE of 23.75%.In addition,this interface engineering modification strategy also greatly improved the long-term stability and light stability of PSCs.（2）Secondly,a bilayer interface engineering modification strategy was developed to incorporate natural vitamin C（VC）into ETL,while vitamin D2（VD2）was added to perovskite.VC increased the electrical conductivity of SnO₂ and reduced the oxygen vacancies on the surface of SnO₂ films,showing improved electron mobility,reduced interfacial energy level shift,and enhanced interfacial charge transfer.VD2 makes the surface energy of perovskite change from n-type to p-type,and the thickness of p-type perovskite is about 80 nm,therefore,during the defect passivation process induced by the VD2 additive,a spontaneous n–p homojunction is formed in the perovskite,which increases the built-in electric field and improves the efficiency of hole extraction from the perovskite.As a result,the improved device achieved a PCE of 24.20%and an fill factor of 81.01%with negligible hysteresis,moreover,the unpackaged device exhibited excellent stability,maintaining an initial efficiency of 93.04%for up to 5000 hours at room temperature.（3）Thirdly,using the interfacial double ETLs multifunctional modification strategy,Ce O_X was introduced at the SnO₂/perovskite interface in PSCs,Ce O_X has good electron transport ability,which not only enhances the electron transport ability but also improves the crystalline quality of the perovskite layer.In addition,Ce O_X with a suitable conduction band can accelerate the extraction and transport of electrons from perovskite to ETL,which can achieve better electron transport,and can also prevent reverse electron transfer and suppress charge carrier recombination.Through this design,we obtained a PCE of 23.82%,and the photostability was greatly improved while suppressing the hysteresis effect.（4）Finally,a novel multifunctional modification strategy of interfacial double ETLs（SnO₂/Ce O_X）was employed to fabricate PSCs,and luminescent Cs Pb Cl₃:Mn²⁺perovskite quantum dots were sandwiched between the two ETLs,which exhibited robust stability and nearly 100%photoluminescence quantum yield.The key is to give full play to the UV response of the fluorescent layer and avoid its interdiffusion with the perovskite layer.This ingenious design not only prevents the quantum dots from diffusing into the perovskite absorber layer,but also reduces the interfacial energy level shift and improves the electron transport capability.As a result,PSCs exhibited the best PCE of 24.32%and significantly improved photostability.Furthermore,we added another luminescence conversion layer in front of the device,and finally obtained a PCE of 24.63%,which is optimal among photoluminescence conversion PSCs.In addition,the addition of fluorescence conversion materials extends the response of PSCs to ultraviolet light,and greatly improves the ultraviolet stability of PSCs,which can make up for the shortcoming of its insufficient utilization of ultraviolet light.