PPV derivatives, polymers with vinylene units, have their tendency to exhibit degradation, after irradiation with white
light or operation of the device, resulting in the appearance of a shifted absorption and emission band in the short
wavelength regions of the spectra. In order to reduce oxidation of the vinylene group, the vinylene group was cyclized
using two 5-membered rings. In this paper, we report the synthesis and properties of new copolymers utilizing
poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1-a]indene-2,7-diyl) (PININE) and benzothiadiazole (BT).
PININE copolymers with BT and thiophene units exhibit high PCE for polymer solar cells (PSCs). Under white light
illumination (AM 1.5 G, 100 mW/cm2), the cell based on PININEDTBT/PCBM as the active layer has a short circuit
current density (Isc) of 5.93 mA/cm2, a fill factor (FF) of 43 %, and PCE of 1.88 %. These copolymers have not only
good processability due to indenoindene unit, in which four alkyl groups can be incorporated, but also the strong and
uniform absorbance in the whole visible region.