Naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-Containing π-Conjugated Compound: Nonfullerene Electron Acceptor for Organic Photovoltaics

• Published in: Advanced functional materials Vol. 26; no. 8; pp. 1161 - 1168
• Main Authors: Chatterjee, Shreyam, Ie, Yutaka, Karakawa, Makoto, Aso, Yoshio
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 23.02.2016
• Subjects: Acceptor materials; Blends; Devices; Energy conversion efficiency; Guidelines; nonfullerene acceptor; organic electronics; organic semiconducting materials; Photovoltaic cells; Solar cells; structure-property relationships; Terminals
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201504153

The development of nonfullerene acceptor materials applicable to organic photovoltaics (OPVs) has attracted considerable attention for the achievement of a high power conversion efficiency (PCE) in recent years. However, it is still challenging due to the insufficiency of both the variety of effective electron‐deficient units and certain guidelines for the design of such materials. This work focusses on naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NTz) as a key electron‐deficient unit. Therefore, a new electron‐accepting π‐conjugated compound (NTz‐Np), whose structure is based on the combination of NTz and the fluorene‐containing imide‐annelated terminal units (Np), is designed and synthesized. The NTz‐Np compound exhibits a narrow optical energy gap (1.73 eV), a proper energy level (−3.60 eV) of the lowest unoccupied molecular orbital, and moderate electron mobility (1.6 × 10−5 cm2 V−1 s−1), indicating that NTz‐Np has appropriate characteristics as an acceptor against poly(3‐hexylthiophene) (P3HT), a representative donor. OPV devices based on NTz‐Np under the blend with P3HT show high photovoltaic performance with a PCE of 2.81%, which is the highest class among the P3HT/nonfullerene‐based OPVs with the conventional device structure. This result indicates that NTz unit can be categorized as a potential electron‐deficient unit for the nonfullerene acceptors. An electron‐accepting π‐conjugated compound based on naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole is designed and synthesized as a nonfullerene acceptor material in organic photovoltaics. Photophysical and electrochemical measurements indicate that this compound has appropriate properties for photovoltaic application. Bulk‐heterojunction solar cells using a blend film of P3HT and the synthesized acceptor as an active layer show photovoltaic characteristics with power conversion efficiencies of up to 2.81%.