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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.


EQE, IQE, and UV–vis absorption spectra for devices A (a), B (b), and E (c).
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f4: EQE, IQE, and UV–vis absorption spectra for devices A (a), B (b), and E (c).

Mentions: The external quantum efficiency (EQE) and estimated internal quantum efficiency (IQE) of the three devices are plotted with UV–vis absorption spectra of the organic films in Figure 4. Since the absorption of DTA extends only up to ca. 450 nm26, PC71BM is mostly responsible for the photocurrent sensitivity in the longer wavelength region (450–700 nm). The p–n device A showed higher absorbance than the BHJ device B; however, it gave significantly lower EQE of only 20% at maximum (Figure 4a) and thus lower IQE. This low IQE in device A is assumed to originate from the planar-junction structure, which is disadvantageous for charge photogeneration because of the limited donor–acceptor (D–A) interface area and the short exciton diffusion length in organic films (ca. 3.1 nm in PC71BM)34. Device B showed weaker absorption peaks (Figure 4b) because of the lower PC71BM content, while its active-layer thickness is similar to that of the p–n device A (75 and 67 nm for devices A and B, respectively). Nevertheless, the BHJ device showed higher sensitivity than the p–n device, associated with much higher IQE of 50% at the absorption maximum of DTA around 420 nm. This indicates that the blend film prepared by the photoprecursor approach is advantageous for charge-carrier photogeneration owing to the large D–A interface area within the film, allowing more excitons to reach the interface to dissociate as in the case of those BHJ films prepared by conventional deposition methods. Device E has the thickest active layer (123 nm) among the three devices; however, its IQE remains at a relatively high level to reach around 45% at maximum (Figure 4c). Thus, the employment of triple-layer structure in this case did not negatively affect the photocurrent generation efficiency as compared to the BHJ system.


Photoprecursor approach as an effective means for preparing multilayer organic semiconducting thin films by solution processes
EQE, IQE, and UV–vis absorption spectra for devices A (a), B (b), and E (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384075&req=5

f4: EQE, IQE, and UV–vis absorption spectra for devices A (a), B (b), and E (c).
Mentions: The external quantum efficiency (EQE) and estimated internal quantum efficiency (IQE) of the three devices are plotted with UV–vis absorption spectra of the organic films in Figure 4. Since the absorption of DTA extends only up to ca. 450 nm26, PC71BM is mostly responsible for the photocurrent sensitivity in the longer wavelength region (450–700 nm). The p–n device A showed higher absorbance than the BHJ device B; however, it gave significantly lower EQE of only 20% at maximum (Figure 4a) and thus lower IQE. This low IQE in device A is assumed to originate from the planar-junction structure, which is disadvantageous for charge photogeneration because of the limited donor–acceptor (D–A) interface area and the short exciton diffusion length in organic films (ca. 3.1 nm in PC71BM)34. Device B showed weaker absorption peaks (Figure 4b) because of the lower PC71BM content, while its active-layer thickness is similar to that of the p–n device A (75 and 67 nm for devices A and B, respectively). Nevertheless, the BHJ device showed higher sensitivity than the p–n device, associated with much higher IQE of 50% at the absorption maximum of DTA around 420 nm. This indicates that the blend film prepared by the photoprecursor approach is advantageous for charge-carrier photogeneration owing to the large D–A interface area within the film, allowing more excitons to reach the interface to dissociate as in the case of those BHJ films prepared by conventional deposition methods. Device E has the thickest active layer (123 nm) among the three devices; however, its IQE remains at a relatively high level to reach around 45% at maximum (Figure 4c). Thus, the employment of triple-layer structure in this case did not negatively affect the photocurrent generation efficiency as compared to the BHJ system.

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.