Fluorobenzotriazole (FTAZ)‐Based Polymer Donor Enables Organic Solar Cells Exceeding 12% Efficiency

Abstract

The fluorobenzotriazole (FTAZ)‐based copolymer donors are promising candidates for nonfullerene polymer solar cells (PSCs), but suffer from relatively low photovoltaic performance due to their unsuitable energy levels and unfavorable morphology. Herein, three polymer donors, L24, L68, and L810, based on a chlorinated‐thienyl benzodithiophene (BDT‐2Cl) unit and FTAZ with different branched alkyl side chain, are synthesized. Incorporation of a chlorine (Cl) atom into the BDT unit is found to distinctly optimize the molecular planarity, energy levels, and improve the polymerization activity. Impressively, subtle side chain length of FTAZ realizes a dramatic improvement in all the device parameters, as revealed by the short‐current density (Jsc) improved from 7.41 to 20.76 mA cm−2, fill‐factor from 36.3 to 73.5%, and even the open‐circuit voltage (Voc) from 0.495 to 0.790 V. The best power conversion efficiency (PCE) of 12.1% is obtained from the L810‐based device, which is one of the highest values reported for FTAZ‐based PSCs so far. Notably, the corresponding external quantum efficiency curve keeps a very prominent value up to 80% from 500 to 800 nm. The notable performance is discovered from the reduced energy loss, improved molecular face‐on orientation, the down‐shifted energy levels, and optimized absorption coefficient regulated by side‐chain engineering.

Non‐Fullerene Organic Solar Cells Based on Benzo[1,2‐b:4,5‐b′]difuran‐Conjugated Polymer with 14% Efficiency

“…In this study, a novel wide‐bandgap BDF‐based copolymer L2 was designed and synthesized using a BDF building block (with conjugated side chains containing chlorinated thiophene) as the electron‐sufficient unit and fluorinated benzotriazole (BTz) as the electron‐deficient unit. In addition, the BDT‐based analogue, referred to as L68, was also synthesized for comparison. Moreover, an A‐D‐π‐A‐type SMA TTPT‐T‐4F was synthesized, whose absorption spectra are complementary with L2 and L68.…”

Chlorination strategy on polymer donors toward efficient solar conversions

“…Bulk heterojunction (BHJ) polymer solar cells (PSCs), comprising conjugated polymer as electron donor and fullerene or nonfullrene derivatives as electron acceptor, have been drawing extensive attentions because of their advantages of low cost, large-area solution processability, light weight, mechanical flexibility and the great potential for commercial applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . Especially the nonfullerence polymer solar cells have shown a new direction for photovoltaic study due to the rapid development in PCE [21][22][23][24] .…”

Wide bandgap polymer donors for high efficiency non-fullerene acceptor based organic solar cells

“…Polymers based on BDT and FBTA units showed high cell performance when blended with ITIC. Liao et al 144 optimized the side chains on FBTA units and introduced Cl atom onto BDT units to synthesize PN8 in order to optimize the planarity, aggregation property, light-harvesting ability, energy levels, molecular face-on orientation, and packing distance. The devices based on PN8 (L810):IT-4F showed a high PCE of 12.1%.…”