Organic photovoltaic (OPV) cells have recently attracted attention as a renewable, sustainable source of electricity, because they are a clean energy source, have a low fabrication cost, and can be processed on a flexible substrate. Therefore, in this study, we investigated the dependency of the pow...
Organic photovoltaic (OPV) cells have recently attracted attention as a renewable, sustainable source of electricity, because they are a clean energy source, have a low fabrication cost, and can be processed on a flexible substrate. Therefore, in this study, we investigated the dependency of the power conversion efficiency (PCE) on the thickness of donor (copper phthalocyanine; CuPc), acceptor (fullerene; C60), and hole/exciton blocking (2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline; BCP) layers and demonstrated mechanism on the donor, acceptor, and hole/exciton blocking layer thickness in the small-molecular photovoltaic cells. The PCE peaked at a specific layer thickness, ~12.7 nm for the donor (CuPc) layer, ~17.5 nm for the acceptor (C60) layer, and ~8.0 nm for the hole/exciton blocking (BCP) layer. In case of donor (CuPc) layer, this is associated with the light absorption and carrier transport resistance, both of which strongly depend on the layer thickness. In other case, this is likely associated with the difference in carrier mobility and in the wavelength of absorbed light. Note that the electron mobility of the acceptor (C60) layer was 100 times faster than the hole mobility of the donor (CuPc) layer. For OPV cells the thickness optimization of donor, acceptor, and hole/exciton layers and the choice of donor layer material with a higher generation rate of exciton after light absorption are key engineering for obtaining maximum PCE. In addition, we discussed about interface (PEDOT:PSS and LiF), P3HT:PCBM weight, hole/exciton blocking (BCP), and top electrode effect in the polymer PV cells. First, the PEDOT:PSS layer was observed that the PCE rapidly increased with a PEDOT:PSS thickness of up to ~2,000 rpm and rapidly decreased when the PEDOT:PSS was thicker than ~2,000 rpm. In addition, the PCE slightly increased with a LiF layer thickness of up to ~0.5 nm and rapidly decreased when the LiF layer was thicker than ~0.5 nm. Second, we found that the PCE shows a similar tendency with short-circuit current (Jsc), rather than with the open-circuit voltage (Voc) and fill factor (FF), as P3HT weight varies, and, the PCE shows a similar tendency with FF, rather than Jsc and Voc, as PCBM weight varies. Third, we demonstrated that the PCE strongly depends on the thickness of the BCP layer. The PCE rapidly increased at a BCP thickness of up to ~1.0 nm and then slightly increased at thicknesses up to ~12.0 nm. Finally, we confirmed that the reflectivity and surface roughness of the metal cathodes correlated well with the Jsc influenced by visible absorption of light reflected from the cathodes. Consequently, the PV cell of high PCE fabricated with a good reflection electrode and surface roughness results in improved performance of the PV cell.
Organic photovoltaic (OPV) cells have recently attracted attention as a renewable, sustainable source of electricity, because they are a clean energy source, have a low fabrication cost, and can be processed on a flexible substrate. Therefore, in this study, we investigated the dependency of the power conversion efficiency (PCE) on the thickness of donor (copper phthalocyanine; CuPc), acceptor (fullerene; C60), and hole/exciton blocking (2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline; BCP) layers and demonstrated mechanism on the donor, acceptor, and hole/exciton blocking layer thickness in the small-molecular photovoltaic cells. The PCE peaked at a specific layer thickness, ~12.7 nm for the donor (CuPc) layer, ~17.5 nm for the acceptor (C60) layer, and ~8.0 nm for the hole/exciton blocking (BCP) layer. In case of donor (CuPc) layer, this is associated with the light absorption and carrier transport resistance, both of which strongly depend on the layer thickness. In other case, this is likely associated with the difference in carrier mobility and in the wavelength of absorbed light. Note that the electron mobility of the acceptor (C60) layer was 100 times faster than the hole mobility of the donor (CuPc) layer. For OPV cells the thickness optimization of donor, acceptor, and hole/exciton layers and the choice of donor layer material with a higher generation rate of exciton after light absorption are key engineering for obtaining maximum PCE. In addition, we discussed about interface (PEDOT:PSS and LiF), P3HT:PCBM weight, hole/exciton blocking (BCP), and top electrode effect in the polymer PV cells. First, the PEDOT:PSS layer was observed that the PCE rapidly increased with a PEDOT:PSS thickness of up to ~2,000 rpm and rapidly decreased when the PEDOT:PSS was thicker than ~2,000 rpm. In addition, the PCE slightly increased with a LiF layer thickness of up to ~0.5 nm and rapidly decreased when the LiF layer was thicker than ~0.5 nm. Second, we found that the PCE shows a similar tendency with short-circuit current (Jsc), rather than with the open-circuit voltage (Voc) and fill factor (FF), as P3HT weight varies, and, the PCE shows a similar tendency with FF, rather than Jsc and Voc, as PCBM weight varies. Third, we demonstrated that the PCE strongly depends on the thickness of the BCP layer. The PCE rapidly increased at a BCP thickness of up to ~1.0 nm and then slightly increased at thicknesses up to ~12.0 nm. Finally, we confirmed that the reflectivity and surface roughness of the metal cathodes correlated well with the Jsc influenced by visible absorption of light reflected from the cathodes. Consequently, the PV cell of high PCE fabricated with a good reflection electrode and surface roughness results in improved performance of the PV cell.
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