Impact of Incorporating Nitrogen Atoms in Naphthalenediimide-Based Polymer Acceptors on the Charge Generation, Device Performance, and Stability of All-Polymer Solar Cells
- Authors
- Kim, Sang Woo; Wang, Yang; You, Hoseon; Lee, Wonho; Michinobu, Tsuyoshi; Kim, Bumjoon J.
- Issue Date
- 2-Oct-2019
- Publisher
- AMER CHEMICAL SOC
- Keywords
- all-polymer solar cells; naphthalenediimide (NDI); polymer acceptor; nitrogen atom; charge generation
- Citation
- ACS APPLIED MATERIALS & INTERFACES, v.11, no.39, pp.35896 - 35903
- Journal Title
- ACS APPLIED MATERIALS & INTERFACES
- Volume
- 11
- Number
- 39
- Start Page
- 35896
- End Page
- 35903
- URI
- https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/140
- DOI
- 10.1021/acsami.9b12037
- ISSN
- 1944-8244
- Abstract
- Substitution of C atoms in a polymer backbone by N atoms allows for the facile tuning of the energy levels as well as the backbone conformation and packing structures of conjugated polymers. Herein, we report a series of three polymer acceptors (P(A)s) with N atoms introduced at different positions of the backbone and investigate how these N atoms affect the device performances of all-polymer solar cells(all-PSCs). The three P(A)s, namely, P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz), are composed of naphthalenediimide (NDI)-based and benzothiadiazole (BT)-based derivatives (dithiophene-BT (BTT), dithiophene-thiadiazolepyridine (PTT), and dithiazole-BT (BTTz)). The PTT and BTTz units are synthesized by replacing the C atoms in BT and thiophene, respectively, with N atoms, which effectively tune the optical, electrochemical, and charge-transporting properties of the corresponding P(A)s. The all-PSCs using poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl))benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di (5-thiophene-2-yl)-5,7-bis (2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)] (PBDB-T) as a polymer donor and P(NDI2DT-PTT) as P-A exhibit a significantly enhanced power conversion efficiency (PCE) of 6.95%, whereas the all-PSCs based on the other P(A)s show relatively lower PCEs (6.02% for PBDB-T:P(NDI2DT-BTT) and 1.43% for PBDB-T:P(NDI2DT-BTTz)). The high PCE of the PBDB-T:P(NDI2DT-PTT) device is due to the superior charge transfer and charge dissociation, resulting from the closely matched energy levels between PBDB-T and P(NDI2DT-PTT), as well as a more favorable bulk heterojunction morphology with improved miscibility. Importantly, the P(NDI2DT-PTT)-based all-PSC device shows improved air stability compared to the P(NDI2DT-BTT)-based device, which is most likely due to a decreased lowest unoccupied molecular orbital level of the P-A. Our findings suggest that the incorporation of N atoms into the P(A)s is an effective strategy for improving the efficiency and stability of all-PSCs.
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