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Photoprecursor approach as an effective means for preparing multilayer organic semiconducting thin films by solution processes

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ABSTRACT

The vertical composition profile of active layer has a major effect on the performance of organic photovoltaic devices (OPVs). While stepwise deposition of different materials is a conceptually straightforward method for controlled preparation of multi-component active layers, it is practically challenging for solution processes because of dissolution of the lower layer. Herein, we overcome this difficulty by employing the photoprecursor approach, in which a soluble photoprecursor is solution-deposited then photoconverted in situ to a poorly soluble organic semiconductor. This approach enables solution-processing of the p-i-n triple-layer architecture that has been suggested to be effective in obtaining efficient OPVs. We show that, when 2,6-dithienylanthracene and a fullerene derivative PC71BM are used as donor and acceptor, respectively, the best p-i-n OPV affords a higher photovoltaic efficiency than the corresponding p-n device by 24% and bulk-heterojunction device by 67%. The photoprecursor approach is also applied to preparation of three-component p-i-n films containing another donor 2,6-bis(5′-(2-ethylhexyl)-(2,2′-bithiophen)-5-yl)anthracene in the i-layer to provide a nearly doubled efficiency as compared to the original two-component p-i-n system. These results indicate that the present approach can serve as an effective means for controlled preparation of well-performing multi-component active layers in OPVs and related organic electronic devices.

No MeSH data available.


Tapping-mode AFM images of a pure DTA film (a), DTA:PC71BM (2:1) blend film (b), pure EH-DBTA film (c), and EH-DBTA:PC71BM (2:1) blend film (d).
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f6: Tapping-mode AFM images of a pure DTA film (a), DTA:PC71BM (2:1) blend film (b), pure EH-DBTA film (c), and EH-DBTA:PC71BM (2:1) blend film (d).

Mentions: To clarify the relationship between film structure and device performance, surface morphologies of a pure DTA film (p-layer) and a DTA:PC71BM blend film (i-layer) were observed by atomic force microscopy (AFM) as shown in Figure 6a and b. The pure DTA film exhibited granular features of several hundred nanometers in diameter; in contrast, the blend film exhibited a “sea–island” structure where aggregated grains (“islands”) of ca. 200–250 nm were observed in the “sea” having a smooth surface. The root-mean square (RMS) values of surface roughness are 19.4 nm for the pure film and 14.1 nm for the blend film. The shapes of grains observed in the DTA:PC71BM blend film is similar to those in the DTA neat film, suggesting that the major component of these grains is DTA. In contrast, no pronounced structure was seen in the sea part, implying that grains of DTA are eroded by mixing with PC71BM, and the smooth composite based on relatively well-mixed DTA and PC71BM fills the gap between grains. (More detailed analysis of the component distribution in this “sea–island” structure will be reported elsewhere.)


Photoprecursor approach as an effective means for preparing multilayer organic semiconducting thin films by solution processes
Tapping-mode AFM images of a pure DTA film (a), DTA:PC71BM (2:1) blend film (b), pure EH-DBTA film (c), and EH-DBTA:PC71BM (2:1) blend film (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384075&req=5

f6: Tapping-mode AFM images of a pure DTA film (a), DTA:PC71BM (2:1) blend film (b), pure EH-DBTA film (c), and EH-DBTA:PC71BM (2:1) blend film (d).
Mentions: To clarify the relationship between film structure and device performance, surface morphologies of a pure DTA film (p-layer) and a DTA:PC71BM blend film (i-layer) were observed by atomic force microscopy (AFM) as shown in Figure 6a and b. The pure DTA film exhibited granular features of several hundred nanometers in diameter; in contrast, the blend film exhibited a “sea–island” structure where aggregated grains (“islands”) of ca. 200–250 nm were observed in the “sea” having a smooth surface. The root-mean square (RMS) values of surface roughness are 19.4 nm for the pure film and 14.1 nm for the blend film. The shapes of grains observed in the DTA:PC71BM blend film is similar to those in the DTA neat film, suggesting that the major component of these grains is DTA. In contrast, no pronounced structure was seen in the sea part, implying that grains of DTA are eroded by mixing with PC71BM, and the smooth composite based on relatively well-mixed DTA and PC71BM fills the gap between grains. (More detailed analysis of the component distribution in this “sea–island” structure will be reported elsewhere.)

View Article: PubMed Central - PubMed

ABSTRACT

The vertical composition profile of active layer has a major effect on the performance of organic photovoltaic devices (OPVs). While stepwise deposition of different materials is a conceptually straightforward method for controlled preparation of multi-component active layers, it is practically challenging for solution processes because of dissolution of the lower layer. Herein, we overcome this difficulty by employing the photoprecursor approach, in which a soluble photoprecursor is solution-deposited then photoconverted in situ to a poorly soluble organic semiconductor. This approach enables solution-processing of the p-i-n triple-layer architecture that has been suggested to be effective in obtaining efficient OPVs. We show that, when 2,6-dithienylanthracene and a fullerene derivative PC71BM are used as donor and acceptor, respectively, the best p-i-n OPV affords a higher photovoltaic efficiency than the corresponding p-n device by 24% and bulk-heterojunction device by 67%. The photoprecursor approach is also applied to preparation of three-component p-i-n films containing another donor 2,6-bis(5′-(2-ethylhexyl)-(2,2′-bithiophen)-5-yl)anthracene in the i-layer to provide a nearly doubled efficiency as compared to the original two-component p-i-n system. These results indicate that the present approach can serve as an effective means for controlled preparation of well-performing multi-component active layers in OPVs and related organic electronic devices.

No MeSH data available.