Title: Improved performance by morphology control via fullerenes in PBDT-TBT-alkoBT based organic solar cells

Abstract

In this work, we report improved performance by controlling morphology using different fullerene derivatives in poly{2-octyldodecyloxy-benzo[1,2-b;3,4-b]dithiophene-alt-5,6-bis(dodecyloxy)-4,7- di(thieno[3,2-b]thiophen-2-yl)-benzo[c][1,2,5]thiadiazole} (PBDT-TBT-alkoBT) based organic solar cells. PC60BM and PC70BM fullerenes were used to investigate the characteristic change in morphology and device performance. Fullerene affects device efficiency by changing active layer morphology. PC70BM with broader absorption than PC₆₀BM resulted in reduced device performance which was elucidated by the intermixed granular morphology separating each larger grain in the PC70BM/polymer composite layer which created higher density of traps. However after adding additive 1,8-diiodooctane (DIO), the fibrous morphology was observed due to reduced solubility of polymer and increased solubility of PC₇₀BM in chloroform. The fibrous morphology improved charge transport leading to increase in overall device performance. Atomic force microscopies (AFM), photo induced charge extraction by linearly increasing voltage (photo-CELIV), and Kelvin prove force microscope (KPFM) were used to investigate nanoscale morphology of active layer with different fullerene derivatives. For PC₆₀BM based active layer, AFM images revealed dense fibrous morphology and more distinct fibrous morphology was observed by adding DIO. The PC₇₀BM based active layer only exhibited intermixed granular morphology instead of fibrous morphology observed in PC60BM based active layer. However, addition of DIO in PC₇₀BM based active layermore » led to fibrous morphology. When additive DIO was not used, a wider distribution of surface potential was observed for PC₇₀BM than PC₆₀BM based active layer by KPFM measurements, indicating 2 polymer and fullerene domains are separated. When DIO was used, narrower distribution of surface potential for both PC₇₀BM and PC₆₀BM based active layers was observed. Photo-CELIV experiment showed larger extracted charge carrier density and mobility in PC₇₀BM/DIO film.« less

Authors:

Khatiwada, Devendra ^[1]; Venkatesan, Swaminathan ^[1]; Chen, QIliang ^[1]; Chen, Jihua ^[2]; Adhikari, Nirmal ^[1]; Dubey, Ashish ^[1]; Mitul, Abu Farzan ^[1]; Mohammed, Lal ^[1]; Qiao, Qiquan ^[1]

---

+ Show Author Affiliations

1. South Dakota State Univ., Brookings, SD (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Fri Jul 03 00:00:00 EDT 2015

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1286906

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Materials Chemistry. A

Additional Journal Information:

Journal Volume: 3; Journal Issue: 29; Journal ID: ISSN 2050-7488

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY