Study On Device Performance And Mechanism Of P3HT:NFA-Based Organic Solar Cell

Bulk heterojunction（BHJ）organic solar cells（OSCs）have attracted extensive attention because of their flexibility,light weight,solution processability and large-area printing.With the development of a variety of new polymer donor materials,the energy conversion efficiency（PCE）of BHJOSCs has increased rapidly in the past few years.Compared with common donor acceptor（D-A）structural polymers,poly（3-hexylthiophene）（P3HT）has the remarkable advantages of simple synthesis,low cost and large-scale manufacturing,so it has broad prospects for industrial production and application.Non-fullerene acceptors（NFAs）can adjust the absorption spectrum and energy level through structural modification,better match with P3HT donors,and can give full play to the advantages of P3HT.Therefore,P3HT:NFA OSCs have developed rapidly in recent years,but it is still of great significance and challenge to study the non-fullerene acceptors well matched with P3HT and explore their structure-activity relationship.This paper started with benzotriazole（BTA）-based non fullerene acceptors blended with P3HT,and studied their structure property relationship in P3HT-based devices.It mainly includes the following research contents:1.Five new materials BTA3b-3f were synthesized by modifying the side chains at three different positions of the classical A₂-A₁-D-A₁-A₂ type non-fullerene acceptor BTA3.The effects of different side chains on photoelectric properties,film morphology,charge carrier behavior and photovoltaic properties were deeply studied.Five bta3x receptors obtained device efficiencies of 5.95,3.80,4.74,5.48 and 6.15%in P3HT-based devices,respectively.The study on the structure-activity relationship shows that the change of the side chain of the central D unit significantly affects the light absorption and film morphology.The alkyl chains with different lengths in the BTA π-bridge unit can adjust the crystallinity and phase separation of the blend film,while the aromatic substituents such as thiophene ring at the end A₂ can fine tune the intermolecular interaction and stacking to achieve smoother and more efficient charge transfer.2.Two acceptors BTA91 and BTA93 with novel A₂-A₁-DA₁D-A₁-A₂ structure were designed and synthesized by replacing the IDT central core of the classical BTA series acceptors with DA₁D fused core containing electron deficient heterocyclic BTA.Compared with BTA91 with cyano end-capping group,BTA93 with cyano group around tannin group has red shift absorption and energy level increase.Its P3HT-based device shows more efficient charge transfer,less charge recombination and moderate phase separation morphology.The PCE of P3HT:BTA91 and P3HT:BTA93 devices were 2.03%and 5.46%respectively.The results show that the new DA₁D structure has great prospects in the design of NFAS for P3HT-based devices.3.A-DA’D-A type NFAs with BTA as A’ unit are firstly used in P3HT-based devices,including the classical Y18 and the new acceptor TPBTA-RCN obtained by replacing end-capping group of Y18 with cyano rhodanine.P3HT:Y18 device has broad absorption spectra,however a poor PCE of 2.66%with a low VOC of 0.41 V were obtained owing to the unsuitable energy levels.After the end-capping group modification of the acceptor,P3HT:TPBTA-RCN still exhibits an improved PCE of 5.23%at the sacrifice of partial light absorption,benefiting from the enhanced exciton dissociation and charge transport efficiency as well as the reduced charge recombination losses.The results show that modification of end-capping group might be an effective method to adjust the aggregation of materials and optimize the phase separation of P3HT-based OSCs.