Preparation And Performance Of Polymeric Electron Transport Layers With Thickness-insensitive Characteristic

Polymer solar cells(PSCs)have the advantages of light weight and flexibility,which are considered to be one of the most promising technologies in the future.With the continuous development of donor and acceptor materials,the highest PCE of single-junction PSCs has reached 18%.Interface engineering aims to promote charge transport and collection,which is essential to achieve efficient PSCs.Electron transport layer(ETL)is an important part of the PSC devices,which can reduce the work function of the cathode and the energy barrier between the cathode and the active layer,and promote electron extraction and electron transsport,thereby improving the performance of the PSCs device.In order to meet the requirements of large-scale production technology,ETLs need to be inexpensive,can be processed in low-temperature solutions,do not require high-temperature annealing,and have a certain thickness tolerance.In this dissertation,a polyelectrolyte based on sulfonate anion and a reticulated polyelectrolyte based on naphthalimide derivative were prepared and used as ETLs for PSCs to study the relationship between structure and performance.The specific content is as follows:Two polyelectrolytes PEDETA-MSB and PEDETA-DBB were prepared by one-step quaternization reaction of penta(hydroxyethyl)-diethylenetriamine(PEDETA)with 1,4-butanediol dimethanesulfonate(MSB)and 1,4-dibromobutane(DBB)respectively.The inverted PSCs devices were prepared with PEDETA-MSB and PEDETA-DBB as ETLs,and the influence of counterions(sulfonate anion and bromide anion)on the thickness insensitivity of the ETLs was systematically studied.The results show that PEDETA-MSB based on sulfonate anions exhibits better thickness tolerance than PEDETA-DBB based on bromide anions.When the film thickness of PEDETA-MSB increases from 9 nm to 47 nm,the PCE values of the device based on PTB7-Th:PC₇₁BM blend film reduce from 10.58%to 10.38%,which still maintains 98%of the initial efficiency.When the thickness of PEDETA-DBB film increases from 10 nm to 40 nm,the PCE values decrease from 10.61%to 9.88%,which only maintains 93%of the initial efficiency.A reticulated polyelectrolyte NDINEA-TBHOB is prepared by quaternization reaction with(N,N-dihydroxyethylamino)propyl-naphthalimide(NDINEA)and trifunctional 1,3,5-tribromohexyloxybenzene(TBHOB),and the linear polyelectrolyte NDINEA-DBH was prepared by the quaternization reaction of NDINEA and1,6-dibromohexane(DBH).The inverted PSCs devices were prepared by using them as the ETLs.The results show that NDINEA-TBHOB with a reticulated structure exhibits more excellent thickness insensitivity.The PCE values of the NDINEA-TBHOB and NDINEA-DBH-based devices with PTB7-Th:PC₇₁BM as the active layer are 10.72%and 10.37%,respectively,when the thickness of ETL is 10nm.However,the PCE of the NDINEA-TBHOB-based device is still 10.03%when the film thickness of ETL increases to 50 nm,while the PCE of the NDINEA-DBH-based device is only 9.54%.In non-fullerene devices,the polyelectrolyte NDINEA-TBHOB with reticulated structure characteristics shows better performance than the linear polyelectrolyte NDINEA-DBH and Zn O for reduced interface barrier between the cathode and the active layer.Moreover,NDINEA-TBHOB reduces the series resistance of the device,so it can improve the V_ocand FF values of the devices.The PCE values of the PSCs based on NDINEA-TBHOB are 13.34%and 16.78%when PM6:IT-4F and PM6:Y6 are used as the active layers respectively,which are both higher than those of the PSCs based on NDINEA-DBH and Zn O.The result indicates that NDINEA-TBHOB is an excellent ETL.Our study provides a new strategy and a new insight for designing and exploiting high-performance thickness-insensitive ETLs.