Selenophene vs. thiophene in benzothiadiazole-based low energy gap donor–acceptor polymers for photovoltaic applications

Abstract

A series of low energy gap polymers comprising 2,7-linked carbazole or fluorene units flanked by thiophene or selenophene repeat units as alternating donor units and benzothiadiazole with or without alkoxy substituents as alternating acceptor repeat units is reported. The effects of replacing thiophene with selenophene in this series of polymers on their optical, electrochemical and photovoltaic device performance when fabricated into bulk heterojunction solar cells using PC 70 BM as an acceptor are investigated. Power conversion efficiencies (PCEs) ranging from 3.34 to 5.41% are obtained with these systems. Thiophene-based polymers are found to have higher efficiency compared to comparable selenophene-based polymers. We tentatively explain such differences on the basis of reduced molar absorbance and reduced charge-carrier mobility in the selenophene-based polymers.

The fabrication of polyfluorene and polycarbazole-based photovoltaic devices using an air-stable process route

“…The chemical structure of each of the polymers is shown in Figure 1(a). The PCDTBT, PCDTBT-8, PCDSeBT-8, and PFDT2BT-8 were synthesised using previously published routes 21,22,29 and had molecular weights of 42.2, 78.6, 60.2, and 91.6 kDa, respectively. The PTB7 was purchased from 1-Material and was used without further purification.…”

“…30 The HOMO and LUMO energy levels of the five polymers as determined by cyclic voltammetry are shown in Figure 1(b). 21,22,29,31 For each polymer, we have fabricated OPV devices based on each of the five polymers. In each case, we have fabricated OPV devices based on a standard device architecture of ITO/PEDOT:PSS (30 nm)/active-layer (70-95 nm)/ Ca (5 nm)/Al (100 nm).…”

Selenophene as a Bridge in Molecular Architecture of Benzotriazole Containing Conjugated Copolymers to Gain Insight on Optical and Electrochemical Properties of Polymers

“…The significant change is observed in LUMO energy level. Selenophene substitution causes decrease in LUMO energy level due to the lower ionization potential of selenophene [21][22][23][24][25][26][27][28]. be followed should improve solar light harvesting while maintaining low lying HOMO level.…”

Bulk Heterojunction Solar Cells — Opportunities and Challenges

“…The new building blocks have various electron withdrawing properties and hence are useful in tuning the properties of the polymer materials. The second strategy is to introduce substitutions on the BT unit, such as fluorine atoms [52][53][54][55][56][57][58][59][60], alkoxy groups [61][62][63][64][65], or replacement of C-H with imine nitrogen [66][67][68][69]. More building blocks can be prepared with the combination of these two strategies [70][71][72][73][74][75].…”