Charge Mobility and Recombination in a New Hole Transporting Polymer and Its Photovoltaic Blend

• Published in: ACS applied materials & interfaces Vol. 2; no. 5; pp. 1414 - 1420
• Main Authors: Tan, Mein Jin, Goh, Wei-Peng, Li, Jun, Pundir, Gaurav, Chellappan, Vijila, Chen, Zhi-Kuan
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26.05.2010
• Subjects: Electromagnetic Fields; Materials Testing; Photochemistry - methods; Polymers - chemistry; Polymers - radiation effects; Static Electricity; polymeric solar cells; PhotoCELIV; time of flight photoconductivity; charge transport and recombination
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am100078g

The charge mobility in a new hole transporting polymer, poly(2,6-bis(thiophene-2-yl)-3,5-dipentadecyldithieno[3,2-b;2′,3′-d]thiophene) (PBTDTT-15), and its blend with (6,6)-phenyl-C70-butyric acid methyl ester (PC70BM) in a weight ratio of 1:3 at ambient atmosphere condition was investigated using time-of-flight (TOF) photoconductivity and photoinduced charge extraction by linearly increasing voltage (PhotoCELIV) techniques. The bulk heterojunction based photovoltaic (PV) blend (PBTDTT-15:PC70BM (1:3)) exhibited a promising power conversion efficiency (PCE) of 3.23% under air mass 1.5 global (AM 1.5G) illumination of 100mW/cm2. The charge mobility and recombination properties of the best performing cells were investigated. The hole mobility in the pure PBTDTT-15 was in the range of 4 × 10−4 cm2/(V s), which was reduced almost 5 times in the PBTDTT-15:PC70BM (1:3) blend. The PhotoCELIV transient observed for the photovoltaic (PV) blend was dominated by electrons, with the charge mobility of the order of 10−3 cm2/(V s), and a weak shoulder at a long time scale due to holes. The effective bimolecular recombination coefficient (β) obtained for the PV blend deviated significantly from the Langevin recombination coefficient (βL) indicating a phase-separated morphology. The obtained results indicate that the PBTDTT-15:PC70BM blend can be potential for organic solar cell applications.