An Alcohol-Soluble Polymer Electron Transport Layer Based on Perylene Diimide Derivatives for Polymer Solar Cells

A conjugated alcohol-soluble polymer based on perylene diimide (PDI) and fluorene (PPDI-FN) was designed and synthesized. PPDI-FN can be soluble in methanol solution under the existence of tiny acetic acid, providing a possibility to prepare polymer solar cells (PSCs) by low-cost non-interfacial mixed solution method. The conventional PSCs based on PTB7-Th:PC71BM were fabricated with PPDI-FN as electron transport layer (ETL). Compare with PSCs based on PTB7-Th:PC71BM without ETL, the introduction of PPDI-FN can achieve an enormous enhancement in performance: V oc (open circuit voltage) from 0.75 to 0.80 V, J sc (short-circuit current density) from 15.57 to 16.72 mA/cm2, fill factor) from 55.96% to 68.87%, and power conversion efficiencies from 6.53% to 9.21%, which is better than PFN (8.62%) as an ETL. The performance of PPDI-FN in the device was studied; the results showed a decreased work function and increased electron transportation and conductivity, which are benefits for the cathode to enhance charge extraction efficiency and decrease recombination losses. These results showed that PDIs derivative PPDI-FN has good application prospects as an ETL to realize high-efficient PSCs.