Regioregular Oligomer and Polymer Containing Thieno[3,4-b]thiophene Moiety for Efficient Organic Solar Cells

Abstract

A regioregular conjugated oligomer (MF) and its polymer counterpart (PF) containing a thieno [3,4b]thiophene moiety have been developed. The existence of thieno [3,4-b]thiophene extends the absorption of the molecules to longer wavelengths and increases the current density of solar cell devices using these materials. The regioregularity of the polymers from the incorporation of regioregular oligothiophene fragments also enhances hole mobility. Consequently, the polymers show higher solar energy conversion efficiencies in bulk heterojunction (BHJ) solar cells than the low molecular weight oligomers. Spectroscopic and structural studies reveal that composite films prepared from the polymer exhibit a larger charge carrier density and smaller domain sizes for the electron donor and acceptor than the oligomer counterpart. These results rationalize the origin for the higher solar cell efficiency.

A Benzo[1,2‐b:4,5‐c′]Dithiophene‐4,8‐Dione‐Based Polymer Donor Achieving an Efficiency Over 16%

“…It is well known that the thieno[3,4‐ b ]thiophene (TT) is a very important functional unit that has been extensively adopted in the PTB family donor polymers, which consist of alternating electron‐rich benzo[1,2‐b:4,5‐b′]dithiophene (BDT) units and electron‐deficient TT units, due to its stabilized quinoidal form . Many previous reports have demonstrated that the existence of the TT unit can broaden the absorption band and extend the polymer absorption range to longer wavelength .…”

Recent Advances in Bulk Heterojunction Polymer Solar Cells

“…Further structural tuning generated the regioregular copolymer PF (Figure 7) incorporating an oligothiophene unit with a PCE of 2.4% in the polymer:PC 61 BM device. 48 A significant breakthrough was made when the PTB polymers, which consist of alternating electron-rich BDT units and electron-deficient TT units, were developed ( Figure 8). 49−51 The PTB family of polymers was designed based on the notion that the polymer must exhibit (1) a narrow band gap for efficient light absorption, (2) proper energy level alignment with the LUMO energy level of PCBM to facilitate charge separation and maximize V oc , (3) high hole mobility for efficient charge transport, and (4) excellent compatibility with PCBM to form a bicontinuous interpenetrating network to maximize exciton separation, migration, and charge transport.…”

Correlation between Exciton Lifetime Distribution and Morphology of Bulk Heterojunction Films after Solvent Annealing

“…To further improve the efficiency of BHJ solar cells, low-bandgap copolymers featuring intramolecular charge transfer interactions between the electron donor and acceptor moieties have been examined extensively. [3][4][5][6][7][8][9][10][11] Recently, low-bandgap copolymers comprising cyclopentadithiophene (CPDT) units have been applied widely in OPV devices. 7,12,13 CPDT-basedcopolymersexhibitrelativelylargechargemobilities 11,14,15 because of their greater π-conjugation lengths and planar molecular geometries relative to those of polythiophene and polyfluorene derivatives; as a result, they are among the most promising candidates for the development of high-efficiency polymer solar cells.…”