Side-Chain Isomerization on an n-type Organic Semiconductor ITIC Acceptor Makes 11.77% High Efficiency Polymer Solar Cells

Abstract

Low bandgap n-type organic semiconductor (n-OS) ITIC has attracted great attention for the application as an acceptor with medium bandgap p-type conjugated polymer as donor in nonfullerene polymer solar cells (PSCs) because of its attractive photovoltaic performance. Here we report a modification on the molecular structure of ITIC by side-chain isomerization with meta-alkyl-phenyl substitution, m-ITIC, to further improve its photovoltaic performance. In a comparison with its isomeric counterpart ITIC with para-alkyl-phenyl substitution, m-ITIC shows a higher film absorption coefficient, a larger crystalline coherence, and higher electron mobility. These inherent advantages of m-ITIC resulted in a higher power conversion efficiency (PCE) of 11.77% for the nonfullerene PSCs with m-ITIC as acceptor and a medium bandgap polymer J61 as donor, which is significantly improved over that (10.57%) of the corresponding devices with ITIC as acceptor. To the best of our knowledge, the PCE of 11.77% is one of the highest values reported in the literature to date for nonfullerene PSCs. More importantly, the m-ITIC-based device shows less thickness-dependent photovoltaic behavior than ITIC-based devices in the active-layer thickness range of 80-360 nm, which is beneficial for large area device fabrication. These results indicate that m-ITIC is a promising low bandgap n-OS for the application as an acceptor in PSCs, and the side-chain isomerization could be an easy and convenient way to further improve the photovoltaic performance of the donor and acceptor materials for high efficiency PSCs.

An Alkylated Indacenodithieno[3,2‐b]thiophene‐Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses

“…Among the highest performing NFAs, linear rod-like acceptor-donor-acceptor (A-D-A) structures incorporating fused ladder-type aromatics have attracted much interest. Common donor units include 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT) [5][6][7][8][9] and 6,12-dihydro-dithienoindeno [10][11][12][13][14][15][16][17][18] In both cases, the fused core facilitates π-electron delocalization and improves the π-π stacking between molecules, hence enhancing the intrinsic charge carrier mobility.In 2015, Zhan and coworkers reported a new NFA, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11--b′]dithiophene (ITIC) (Scheme 1), which is comprised an electron-donating IDTT-based core flanked by two electron-withdrawing units of 1,1-dicyanomethylene-3-indanone (IC), that exhibited a promising PCE of 6.8% at that time. [10] Since then, many strategies have been applied to modify the structure of ITIC in order to adjust the absorption spectra and energy levels to further improve the PCE, for example, by changing the side chains, [17,18] extending the conjugation length, [19][20][21][22] and substituting the end acceptor groups.…”

“…[13][14][15][16] To date, a few systems based on these NFAs have achieved a PCE of over 10%. [5,[13][14][15]18,20,22] However, it is noticeable that in all cases these NFAs incorporate phenylalkyl or thienylalkyl side chains as the solubilizing groups on the fused core. These aryl-based side chains facilitate the synthesis of the IDTT core under Friedel-Crafts conditions via the formation of stable triaryl cations.…”

“…Among the highest performing NFAs, linear rod-like acceptor-donor-acceptor (A-D-A) structures incorporating fused ladder-type aromatics have attracted much interest. Common donor units include 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT) [5][6][7][8][9] and 6,12-dihydro-dithienoindeno [10][11][12][13][14][15][16][17][18] In both cases, the fused core facilitates π-electron delocalization and improves the π-π stacking between molecules, hence enhancing the intrinsic charge carrier mobility.…”

Environmentally-friendly solvent processed fullerene-free organic solar cells enabled by screening halogen-free solvent additives

“…Great efforts have been made to improve the power conversion effi-ciencies (PCEs) of OSCs by utilizing novel materials and new processing methods over the past decades [1,[20][21][22][23][24][25][26][27][28][29][30][31]. Recently, high-performance non-fullerene acceptor materials, especially the small-molecular acceptors (SMAs), were successfully developed [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. These SMAs materials exhibit excellent solubility in non-halogen solvents, such as o-xylene (XY), anisole and tetrahydrofuran (THF) [46], which have brought the possibility of fabricating high-performance non-fullerene OSCs using non-halogen solvent systems.…”

A New Electron Acceptor with meta‐Alkoxyphenyl Side Chain for Fullerene‐Free Polymer Solar Cells with 9.3% Efficiency

“…Recently, Li and co‐workers have reported an acceptor material m‐ITIC by replacing para ‐alkylphenyl of ITIC with meta ‐alkylphenyl; when m‐ITIC was blended with a polymer donor J61 after thermal annealing (TA) at 130 °C for 5 min, the PCE achieved was 11.77%. The performance is more superior than that of the J61/ITIC blend, because m‐ITIC with meta ‐alkylphenyl instead of para‐alkyl‐phenyl side chains showed higher film absorption coefficient and higher electron mobility compared to its counterpart‐ITIC 37. Based on the above considerations, we first synthesized a new acceptor, namely, m‐ITIC‐OR, based on IDTT as a core with four meta ‐alkoxyphenyl as side chains as well as IC as an end group.…”