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)-4,7di(thieno[3,2-b]thiophen-2-yl)-benzo[c][1,2,5]thiadiazole} (PBDT-TBT-alkoBT) based organic solar cells.PC 60 BM and PC 70 BM fullerenes were used to investigate the characteristic changes in morphology and device performance. Fullerenes affect device efficiency by changing the active layer morphology.PC 70 BM with broader absorption than PC 60 BM resulted in reduced device performance which was elucidated by the intermixed granular morphology separating each larger grain in the PC 70 BM/polymer composite layer which created a higher density of traps. However after adding additive 1,8-diiodooctane (DIO), a fibrous morphology was observed due to the reduced solubility of the polymer and increased solubility of PC 70 BM in chloroform. The fibrous morphology improved charge transport leading to an increase in overall device performance. Atomic force microscopy (AFM), photo-induced charge extraction by linearly increasing voltage (photo-CELIV), and Kelvin probe force microscopy (KPFM) were used to investigate the nanoscale morphology of the active layer with different fullerene derivatives. For the PC 60 BM based active layer, AFM images revealed a dense fibrous morphology and more distinct fibrous morphology was observed by adding DIO. The PC 70 BM based active layer only exhibited an intermixed granular morphology instead of a fibrous morphology observed in the PC 60 BM based active layer. However, addition of DIO into the PC 70 BM based active layer led to fibrous morphology. When additive DIO was not used, a wider distribution of surface potential was observed for PC 70 BM than the PC 60 BM based active layer by KPFM measurements, indicating that polymer and fullerene domains are separated. When DIO was used, a narrower distribution of surface potential for both PC 70 BM and PC 60 BM based active layers was observed. Photo-CELIV experiments showed larger extracted charge carrier density and mobility in the PC 70 BM/DIO film. Fig. 1 (a) Molecular structure, (b) absorbance spectrum, and (c) cyclic voltammograms of PBDT-TBT-alkoBT thin films. J. Mater. Chem. A This journal is

Elevated Stability and Efficiency of Solar Cells via Ordered Alloy Co-Acceptors

“…Herein, PC 61 BM as a third element was incorporated in the PTB7-Th/CO i 8DFIC system to form an ordered alloyed co-acceptor structure with CO i 8DFIC. It is well-known that PC 71 BM is used more frequently compared to PC 61 BM due to its strong light absorption and generally better device performance. − However, we chose PC 61 BM rather than PC 71 BM for the following two reasons. First, PC 61 BM as a third component with very low light absorption can alleviate the influence of light absorption on J sc , which helps us explain the enhancement of J sc clearly.…”

Advanced Electron Microscopy of Nanophased Synthetic Polymers and Soft Complexes for Energy and Medicine Applications

“…Understanding the nanomorphology is critical in order to enhance the power conversion efficiency of organic solar cells [2,5]. Film floating at the water surface, FIB, and EFTEM were used to examine the in-plane and out-of-plane nanomorphology of organic solar cell systems with low-bandgap polymers as p-type components and fullerene derivatives as n-type components [2,21,[34][35][36][37]. The power efficiency of organic solar cells relies on the continuous penetration of interconnected donor-and acceptor-rich domains [38][39][40][41][42][43][44][45][46][47][48][49][50][51].…”

“…Block copolymers with a conjugated polymer component can be imaged without staining because of the crystal packing-induced contrast [55]. For EFTEM experiments, conjugated polymers and organic semiconductors have characteristic features at low-eV plasmon regions (e.g., 19 eV and 30 eV for n-type and p-type materials, respectively) that have much stronger EELS signals and may be used in combination with their core edges [2,21,34,35].…”

Improving the device performance of organic solar cells with immiscible solid additives

“…The general methods used to control the morphology of the photoactive layer include solvent selection, thermal annealing (TA), solvent vapor annealing (SVA), pre-aggregation, additives, etc. 33–38 The key effect on the above mentioned strategy for morphology control lies in tuning the dynamics or kinetics of the donor:acceptor (D:A) phase separation during the solidification process or post-ripening. In particular, the additives are most frequently used and are proved to be critical ingredients for most high-performance OSCs.…”