Synthesis of a Modified PC₇₀BM and Its Application as an Electron Acceptor with Poly(3‐hexylthiophene) as an Electron Donor for Efficient Bulk Heterojunction Solar Cells

A simple and effective modification of phenyl‐C 70 ‐butyric acid methyl ester (PC 70 BM) is carried out in a single step after which the material is used as electron acceptor for bulk heterojunction polymer solar cells (PSCs). The modified PC 70 BM, namely CN‐PC 70 BM, showed broader and stronger absorption in the visible region (350–550 nm) of the solar spectrum than PC 70 BM because of the presence of a cyanovinylene 4‐nitrophenyl segment. The lowest unoccupied molecular energy level (LUMO) of CN‐PC 70 BM is higher than that of PC 70 BM by 0.15 eV. The PSC based on the blend (cast from tetrahydrofuran (THF) solution) consists of P3HT as the electron donor and CN‐PC 70 BM as the electron acceptor and shows a power conversion efficiency (PCE) of 4.88%, which is higher than that of devices based on PC 70 BM as the electron acceptor (3.23%). The higher PCE of the solar cell based on P3HT:CN‐PC 70 BM is related to the increase in both the short circuit current ( J sc ) and the open circuit voltage ( V oc ). The increase in J sc is related to the stronger light absorption of CN‐PC 70 BM in the visible region of the solar spectrum as compared to that of PC 70 BM. In other words, more excitons are generated in the bulk heterojunction (BHJ) active layer. On the other hand, the higher difference between the LUMO of CN‐PC 70 BM and the HOMO of P3HT causes an enhancement in the V oc . The addition of 2% (v/v) 1‐chloronapthalene (CN) to the THF solvent during film deposition results in an overall improvement of the PCE up to 5.83%. This improvement in PCE can be attributed to the enhanced crystallinity of the blend (particularly of P3HT) and more balanced charge transport in the device.