Performance of Donor-Acceptor copolymer materials PCPDTBT and PCDTBT with poly hexyl thiophene polymer in a ternary blend

The efficiency of organic solar cells is limited by the absorbance of the donor and acceptor material in the binary blend. In order to extend the absorption spectrum of the absorbing species, a ternary blend is formed by adding a donor material to the already existing binary blend. In this paper we discuss about the addition of P3HT (Polyhexylthiopene) to either Donor-Acceptor copolymer material PCPDTBT(Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′] di thio phene)-alt-4,7(2,1,3-benzothiadiazole) or PCDTBT (poly [poly [N-9'-heptadecanyl-2.7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole-4,7-diyl-2,5-thio phenediyl) with common acceptor PC₆₀BM (phenyl-C61-butyric acid). Donor-acceptor copolymers are materials with repeated units of electron donor and electron acceptor units connected by a π-conjugated small molecule. Interestingly a decrease in efficiency is observed when P3HT is added to the binary blend of PCDTBT: PCBM and an increase in efficiency is observed when P3HT is added to the binary blend of PCPDTBT: PCBM. There is cascading of energy levels in both the ternary blends PCDTBT: P3HT: PCBM and PCPDTBT: P3HT: PCBM which helps in the movement of free charge carriers. And also the open circuit voltage decreased in both the cases by the addition of P3HT. But the short circuit current density increased in the PCPDTBT: P3HT: PCBM ternary blend due to the improvement in photon absorption. The UV-Vis spectrophotometry, photoluminescence spectrometry, and X-ray diffraction confirm the results.