Abstract
A morphologically-stable polymer/fullerene heterojunction has been prepared by minimizing the intermixing between polymer and fullerene via sequential deposition (SqD) of a polymer and a fullerene solution. A low crystalline conjugated polymer of PCPDTBT (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]) has been utilized for the polymer layer and PC71BM (phenyl-C71-butyric-acid-methyl ester) for the fullerene layer, respectively. Firstly, a nanostructured PCPDTBT bottom layer was developed by utilizing various additives to increase the surface area of the polymer film. The PC71BM solution was prepared by dissolving it in the 1,2-dichloroethane (DCE), exhibiting a lower vapor pressure and slower diffusion into the polymer layer. The deposition of the PC71BM solution on the nanostructured PCPDTBT layer forms an inter-digitated bulk heterojunction (ID-BHJ) with minimized intermixing. The organic photovoltaic (OPV) device utilizing the ID-BHJ photoactive layer exhibits a highly reproducible solar cell performance. In spite of restricted intermixing between the PC71BM and the PCPDTBT, the efficiency of ID-BHJ OPVs (3.36%) is comparable to that of OPVs (3.87%) prepared by the conventional method (deposition of a blended solution of polymer:fullerene). The thermal stability of the ID-BHJ is superior to the bulk heterojunction (BHJ) prepared by the conventional method. The ID-BHJ OPV maintains 70% of its initial efficiency after thermal stress application for twelve days at 80 °C, whereas the conventional BHJ OPV maintains only 40% of its initial efficiency.
Highlights
IntroductionOrganic photovoltaics (OPVs) have exceeded 10% power conversion efficiency (PCE)
Organic photovoltaics (OPVs) have exceeded 10% power conversion efficiency (PCE)by incorporating the finely-controlled bulk heterojunction (BHJ) photoactive layer morphology [1,2,3].Due to the short exciton diffusion length of organic semiconductors, a fine and bi-continuous BHJ morphology is important for a high exciton dissociation efficiency and charge transport efficiency [4].The most widely-utilized method to construct the BHJ morphology is the blended solution deposition (BSD) (Figure 1a), whereby the polymer and fullerene are dissolved in the same solvent and deposited to produce a BHJ layer
BHJ. was applied as a photoactive layer of the organic photovoltaic (OPV), it exhibited superior morphological stability compared to the conventional BHJ
Summary
Organic photovoltaics (OPVs) have exceeded 10% power conversion efficiency (PCE). The most widely-utilized method to construct the BHJ morphology is the blended solution deposition (BSD) (Figure 1a), whereby the polymer and fullerene are dissolved in the same solvent and deposited to produce a BHJ layer. Due to the limited heterojunction area of the photo-active layer fabricated by process (SqD-OPV). The swelling process is sensitive to the fabrication conditions, such fullerene into the polymer layer. We have addressed the [2,1-b;3,4-b above requirements by fabricating a nanostructured poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3(PCPDTBT) (Figure 1c) bottom layer with a proper additive and utilizing 1,2-dichloroethane (DCE), benzothiadiazole)]. 1,2-dichloroethane (DCE), exhibiting a lower vapor pressure and slower diffusion into the polymer phenyl-C. due to as its bulk side chain, and OPV71based on PCPDTBT exhibits poor stability. Was applied as a photoactive layer of the OPV, it exhibited superior morphological stability compared to the conventional BHJ BHJ. was applied as a photoactive layer of the OPV, it exhibited superior morphological stability compared to the conventional BHJ
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