Enhanced performance of inverted organic solar cell by a solution-based fluorinated acceptor doped P3HT:PCBM layer

An inverted organic solar cell based on strong electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped poly (3-hexylthiophene) P3HT: [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was fabricated to figure out the p-type doping effect on the device performance. It was found that the doping concentration played a critical role on the electrical output of the devices. An enhanced power conversion efficiency (PCE) of 4.22% was achieved, in comparison of PCE of 3.68% for the device based on pristine P3HT:PCBM. The topography morphology of the active film, the hole mobility, the ultraviolet–visible absorption spectrum, the photoluminescence (PL) lifetime and the Fermi energy level of P3HT film with and without F4-TCNQ doping were characterized to investigate the doping effect. The measured results indicated that the hole mobility and absorption of P3HT film was slightly modified with F4-TCNQ doping. On the contrary, the active film morphology, the PL lifetime and the Fermi energy level of P3HT changed dramatically with doping. It was found that F4-TCNQ preferred to approach to the air/liquid interface during the solvent dry process, leading to F4-TCNQ-rich upper layer due to its low surface energy. The layer with proper thickness between anode and active layer dramatically improve the interface contact, resulting in the enhanced device performance.

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► The F4-TCNQ doping in P3HT:PCBM plays dominant role on the electric output characteristics.
► The hole mobility of P3HT in bulk heterojunction is slightly enhanced after F4-TCNQ doping.
► The F4-TCNQ addition affects the topography of P3HT:PCBM and improves the contact between active layer and anode.
► The enhanced performance after doping is attributed to the decreased series resistance.