Orientation, Morphology, and Performance of Organic Photovoltaics Based on Diketopyrrolopyrrole-Linked Tetrabenzoporphyrins

Kohtaro Takahashi^a, Naoki Aratani^a, Mitsuharu Suzuki^a, Daiki Kuzuhara^a, Hiroko Yamada^a, Ken-ichi Nakayama^b, Yuji Yamaguchi^b, Naoya Yamada^b, Daichi Kumagai^b, Tomoyuki Koganezawa^c, Sadahiro Masuo^d

^aGraduate School of Materials Science, Nara Institute of Science and Technology - Japan, 8916-5, Takayama-cho, Ikoma, 630, Japan

^bDepartment of Organic Device Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan, Japan

^cJapan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan, Japan

^dDepartment of Applied Chemistry and Environment, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan, Japan

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)

Swansea, United Kingdom, 2016 June 29th - July 1st

Organizers: James Durrant, Henry Snaith and David Worsley

Poster, Kohtaro Takahashi, 239
Publication date: 28th March 2016

Tetrabenzoporphyrin (BP) is one of the prominent p-type materials for organic photovoltaics (OPV). However, BP has two main problems as a p-type material for OPV in case of using PC₆₁BM as an n-type material. Firstly, BP doesn’t have absorption bands over 700 nm, so if we allow BP to have absorption bands in this region, the short-circuit current density (J_SC) of OPV will be improved. Secondly, highest occupied molecular orbital (HOMO) level of BP (–4.9 eV) is higher than ideal HOMO levels (–5.2 to –5.4 eV) in combination with PC₆₁BM. So, if the HOMO level of BP is lower, the open-circuit voltage (V_OC) of OPV will be improved since the V_OC of OPV is proportional to the energy gap between the HOMO level of p-type material and the LUMO level of n-type materials. In this regard, we designed and synthesized diketopyrrolopyrrole (DPP)-linked tetrabenzoporphyrins (Cn-DPP-BPs, n = length of alkyl chains) that have different length of alkyl chains on DPP units. Cn-DPP-BPs showed broader absorption spectra in visible to near infrared light regions and covered over 700 to 900 nm. Furthermore, HOMO levels of Cn-DPP-BPs were 0.1 eV lower than that of BP. We fabricated bulk hetrojunction (BHJ)-type OPVs of Cn-DPP-BP and PC₆₁BM to find that performance of OPVs is strongly depended on the length of alkyl chains. After optimizing the fabrication conditions, a combination with C4-DPP-BP and PC₆₁BM showed the best power conversion efficiency (PCE) of 5.24% and the J_SC and V_OC were improved compared to those of BP/PC₆₁BM devices. We will report the morphology and molecular orientations of BHJ-films.

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