**4. Conclusion**

428 Solar Cells – New Aspects and Solutions

O

+

H17C8O

**P18**

*t*-BuOK

OC8H17

O

H17C8O

O

O

**P20** R1 = R2 = octadecyl R1 = R2 = octyl R1 = R2 = 2-ethylhexyl R1 = 2-ethylhexyl, R = methyl

**P22** R = 2-ethylhexyl or methyl

S

RO

OC8H17

O

O

**P22**

n

OR1

n

n

OR2

O

OC8H17

(EtO)2OP

O

PO(OEt)2

H17C8O

OC8H17

**P21**

H17C8O

X

X = H, R1 = octadecyl, R2 = octyl X = H, R1 = dodecyl, R2 = octyl X = octyloxy, R1 = R2 = octadecyl X = octyloxy, R1 = R2 = octyl X = octyloxy, R1 = R2 = 2-ethylhexyl

**P21** R = 2-ethylhexyl or methyl

S

X

OR1

**P19**

X

X

H17C8O

R1O

OC8H17

O

OC8H17

H H17C8O H

OC8H17

Fig. 15. Synthesis of acetylene-containing **P18** via a Wittig – Horner reaction

OR2

R2O <sup>n</sup>

Fig. 16. Chemical structures of acetylene-containing PPV derivatives **P19-P22**

n

O

RO

The efficiency of organic solar cells is increasing steadily by means of interdisciplinary approach. Extensive efforts are currently carry out by chemists in order to create new low bandgap materials to harvest more photons and increase the power conversion efficiency. Furthermore, processability of conjugated polymers that can be deposited from liquid solutions at low temperature make them suitable for large scale production on flexible substrates at low cost roll-to-roll process. To integrate new advanced device concepts and the nanostructure engineering of the morphology are also important in bringing high efficiency and low cost organic solar cells one step closer to successful commercialization.
