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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.


J–V curves for devices A, B, and E. Solid lines: under AM1.5G illumination at 100 mW cm−2, dashed lines: in the dark.
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f3: J–V curves for devices A, B, and E. Solid lines: under AM1.5G illumination at 100 mW cm−2, dashed lines: in the dark.

Mentions: The photovoltaic performances of the p–n, BHJ, and p–i–n devices prepared using different solution concentrations are summarized in Table 1. We firstly compare three devices A, B, and E in order to elucidate differences originating from the device architecture. Note that the concentrations of deposition solutions are consistent within each layer type (i.e., p-, n-, or i-layer) among these three devices. Their J–V curves in the dark and under AM1.5G illumination are shown in Figure 3. All of the three devices showed open circuit voltages (VOC) of ≥0.8 V, which is reasonable if one considers the relatively large energy difference between the highest occupied molecular orbital (HOMO) of DTA (−5.5 eV)27 and the lowest unoccupied molecular orbital (LUMO) of PC71BM (−4.3 eV)2829. Here, the Voc in an OPV generally correlates to the energy difference between the LUMO of accepter and the HOMO of donor minus the exciton binding energy303132. High Voc of up to ca. 1 V have been observed in polymer/PC71BM systems in which the polymers are similar to DTA in terms of the HOMO level33. The p–n device A yielded a PCE of 1.21% associated with a short circuit current density (JSC) of 2.81 mA cm−2, the highest fill factor (FF) of 53.6%, the lowest series resistance (RS) of 36 Ω cm2, and the highest shunt resistance (RSH) of 2134 Ω cm2. The BHJ device B exhibited a higher JSC of 2.92 mA cm−2, but a significantly lower FF of 29.3%, resulting in a PCE of 0.90%. The homo p–i–n device E gave a good electrical properties with a higher FF of 46.1% and a lower RS of 51 Ω cm2, in spite of the greater overall film thickness (123 nm) as compared to device B (67 nm). As a result, device E achieved the highest JSC of 3.64 mA cm−2 and PCE of 1.38% among the three devices.


Photoprecursor approach as an effective means for preparing multilayer organic semiconducting thin films by solution processes
J–V curves for devices A, B, and E. Solid lines: under AM1.5G illumination at 100 mW cm−2, dashed lines: in the dark.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: J–V curves for devices A, B, and E. Solid lines: under AM1.5G illumination at 100 mW cm−2, dashed lines: in the dark.
Mentions: The photovoltaic performances of the p–n, BHJ, and p–i–n devices prepared using different solution concentrations are summarized in Table 1. We firstly compare three devices A, B, and E in order to elucidate differences originating from the device architecture. Note that the concentrations of deposition solutions are consistent within each layer type (i.e., p-, n-, or i-layer) among these three devices. Their J–V curves in the dark and under AM1.5G illumination are shown in Figure 3. All of the three devices showed open circuit voltages (VOC) of ≥0.8 V, which is reasonable if one considers the relatively large energy difference between the highest occupied molecular orbital (HOMO) of DTA (−5.5 eV)27 and the lowest unoccupied molecular orbital (LUMO) of PC71BM (−4.3 eV)2829. Here, the Voc in an OPV generally correlates to the energy difference between the LUMO of accepter and the HOMO of donor minus the exciton binding energy303132. High Voc of up to ca. 1 V have been observed in polymer/PC71BM systems in which the polymers are similar to DTA in terms of the HOMO level33. The p–n device A yielded a PCE of 1.21% associated with a short circuit current density (JSC) of 2.81 mA cm−2, the highest fill factor (FF) of 53.6%, the lowest series resistance (RS) of 36 Ω cm2, and the highest shunt resistance (RSH) of 2134 Ω cm2. The BHJ device B exhibited a higher JSC of 2.92 mA cm−2, but a significantly lower FF of 29.3%, resulting in a PCE of 0.90%. The homo p–i–n device E gave a good electrical properties with a higher FF of 46.1% and a lower RS of 51 Ω cm2, in spite of the greater overall film thickness (123 nm) as compared to device B (67 nm). As a result, device E achieved the highest JSC of 3.64 mA cm−2 and PCE of 1.38% among the three devices.

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.