A Selenophene Analogue of PCDTBT: Selective Fine-Tuning of LUMO to Lower of the Bandgap for Efficient Polymer Solar Cells

Abstract

In an attempt to further improve the performance of the PCDTBT-based polymer Solar cells (PSCs), we have synthesized a selenophene. analogue of PCDTBT, namely, PCDSeBT, in which diselenienylbenzothiadiazole (DSeBT) monomer alternately flanks with a 2,7-carbazole unit. The intrinsic properties of PCDSeBT are not only characterized by UV-vis absorption, cyclic voltammetry (CV), and organic field-effect transistors (OFETs) but also the surface morphology, mobilities of space charge-limited current (SCLC) model, and polymer solar cells (PSCs) in its bulk-heterojunction (BHJ) active layer with [6,6]-phenyl C-71-butyric acid methyl ester (PC71BM) are evaluated in detail. It is found that PCDSeBT simultaneously has a low-lying highest occupied molecular orbital (HOMO) energy level at -5.4 eV and a low bandgap of 130 eV as required by the ideal polymers for BHJ PSCs. The high current of 11.7 mA/cm(2) is obtained for PCDSeBT-based PSCs, to our knowledge, which is among, the highest short-circuit current density (J(SC)) values obtained from a BIT device consisting of PCDTBT derivatives and [6,6] phenyl C-61-butyric acid methyl ester (PCBM). The high J(SC) value, along with moderate fill factor (FP) of 45% and a high open circuit voltage (V-OC) of 079 V, yields a power conversion efficiency (PCE) of 4:12%, which is about 37% increase in PCE from a PCDTBT-based reference device. On the basis of our results, one can be concluded that the DSeBT placement for construction of donor (D) acceptor (A) polymers is an easy and effective way to realize both the higher J(SC) and V-OC values in PSCs, as a consequence of the selective lower-lying lowest unoccupied molecular orbital (LUMO) with the HOMO being almost unchanged, together with the effective broadening on the absorption band.