Effect of conjugated small molecular electrolytes based on carbazole with N and F atoms for the automatic formation of electron transport layer in polymer solar cell

Abstract

Conjugated small molecular electrolytes (CSMEs), based on carbazole, containing different number of N and F atoms, were synthesized and introduced as the electron transport layer (ETL) for the fabrication of the polymer solar cells. Active-layer materials of bulk heterojunction and synthesized CSMEs were mixed as one solution which was coated on ZnO/ITO in one go to provide the spontaneous phase separation of the active-layer and ETL, which is identified by ToF-SIMS, for the generation of enhanced device performance. Caused by the interaction of the amino groups with ZnO, assisted by the fluorine atoms of the CSMEs, the spontaneous formation of the ETL layer was achieved for the enhancement of the efficiency of the device. The efficiency of polymer solar cells was improved as increasing the number of F atoms (from CzN1 to CzN1F4 and from CzN4 to CzN4F4). It was caused by the introduced F atom which could be led to the n-doping effect. The polymer solar cells utilizing one solution of CzN1F4 and PTB7-Th:PC71BM showed the highest power conversion efficiency (PCE) of 8.93%, with VOC of 0.78 V, Jsc of 16.09 mA/cm2 and FF of 0.72.