Modification of Hole Transport Layers for Fabricating High Performance Non-fullerene Polymer Solar Cells

Interfacial engineering is expected to be a feasible strategy to improve the charge transport properties of the hole transport layer(HTL),which is of crucial importance to boost the device performance of organic solar cells(OSCs).In this study,two types of alcohol soluble materials,2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ)and di-tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ll)(N719)dye were selected as the dopant for HTL.The doping of F4-TCNQ and N719 dye in poly(ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)with and without integrating a graphene quantum-dots(G-QDs)layer has been explored in poly[[2,6'-4-8-di(5-ethylhexylthienyl)benzo[1,2-b:3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thio-phenediyl:(2,2'-((2Z,2'Z)-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-5,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile(PTB7-Th:IEICO-4F)OSCs.The power conversion efficiency of the non-fullerene OSCs has been increased to 10.12%from 8.84%.The influence of HTL modification on the nano-morphological structures and photophysical properties is analyzed based on the comparative studies performed on the control and modified devices.The use of chemical doping and bilayer strategy optimizes the energy level alignment,nanomorphology,hole mobility,and work-function of HTL,leading to considerable reduction of the leakage current and recombination losses.Our work demonstrates that the doping of HTL and the incorporation of G-QDs layer to constitute a bilayer HTL is an promising strategy to fabricate high performance non-fullerene polymer solar cells.