ABSTRACT
We attempted to improve the photon absorption of the photoactive layer in organic photovoltaic (OPV) devices by device engineering without changing their thickness. Soft nanoimprinting lithography was used to introduce a 1D grating pattern into the photoactive layer. The increase in photocurrent caused by the propagating surface plasmon-polariton mode was quantitatively analyzed by measuring the external quantum efficiency in transverse magnetic and transverse electric modes. In addition, the introduction of an ultrathin substrate with a refractive index of 1.34 improved photon absorption by overcoming the mismatched optical impedance at the air/substrate interface. As a result, the power conversion efficiency (PCE) of an ultrathin OPV with a 400 nm grating period was 8.34%, which was 11.6% higher than that of an unpatterned ultrathin OPV, and the PCE was 3.2 times higher at a low incident light angle of 80°, indicating very low incident light angle dependence.
ABSTRACT
We have developed a novel structure of ultra-flexible organic photovoltaics (UFOPVs) for application as a power source for wearable devices with excellent biocompatibility and flexibility. Parylene was applied as an ultra-flexible substrate through chemical vapor deposition. Indium-zinc-tin oxide (IZTO) thin film was used as a transparent electrode. The sputtering target composed of 70 at.% In2O3-15 at.% ZnO-15 at.% SnO2 was used. It was fabricated at room temperature, using pulsed DC magnetron sputtering, with an amorphous structure. UFOPVs, in which a 1D grating pattern was introduced into the hole-transport and photoactive layers were fabricated, showed a 13.6% improvement (maximum power conversion efficiency (PCE): 8.35%) compared to the reference device, thereby minimizing reliance on the incident angle of the light. In addition, after 1000 compression/relaxation tests with a compression strain of 33%, the PCE of the UFOPVs maintained a maximum of 93.3% of their initial value.
ABSTRACT
In this study, ultra-flexible organic photovoltaics (OPVs) with a new device structure are developed as a power source for ultra-flexible wearable devices with excellent biocompatibility. To fabricate ultra-flexible OPVs with excellent mechanical properties, we develop an ultra-flexible substrate with a bilayer structure based on polymers and transparent conducting oxides. An amorphous perfluorinated polymer (cyclic transparent optical polymer, CYTOP) is introduced as an ultra-flexible substrate by a solution process. An indium zinc tin oxide (IZTO) transparent electrode possessing an amorphous structure is fabricated via pulsed DC magnetron sputtering at room temperature using a target containing 80 atom % In2O3-10 atom % ZnO-10 atom % SnO2. Ultra-flexible OPVs with a one-dimensional (1D) grating pattern are fabricated on the buffer layer and photoactive layer. These OPVs exhibit an increase of 12% in power conversion efficiency (PCE) (maximum PCE: 8.52%) compared to the reference, thereby minimizing reliance on the incident angle of light. In addition, even after 1000 compression/relaxation tests with a compression strain of 33%, the PCE of the ultra-flexible OPVs is maintained up to 94.8% of its initial value.
