Abstract Both charge recombination and degradation in sequential solution processed polymer/fullerene bilayer organic photovoltaics (OPV) are effectively reduced by the insertion of a TiO2 inter-layer between the bilayer and Al electrode. The polymer/fullerene bilayer composed of a poly(3-hexylthiophene) (P3HT) bottom-layer and a [6,6] phenyl C61-butyric acid methyl ester (PCBM) top-layer shows significant change in morphology due to the substantial inter-penetration of P3HT and PCBM during the thermal annealing process. Consequently, the bilayer surface becomes P3HT rich resulting in significant charge recombination at the bilayer/Al interface of the bilayer OPV. The charge recombination rate of the bilayer OPV is reduced by one order of magnitude upon the insertion of a TiO2 nanoparticle inter-layer between the bilayer and the Al electrode after the thermal annealing process. In contrast, when the thermal annealing process is conducted after insertion of the inter-layer, the effect of the TiO2 inter-layer becomes insignificant. The VOC and efficiency of the bilayer OPV is greatly enhanced from 0.37 to 0.66 V and 1.2% to 3.7%, respectively by utilizing the properly constructed TiO2 inter-layer in the bilayer OPV. Additionally, insertion of the TiO2 inter-layer significantly improves the stability of the bilayer OPV. The bilayer OPV with a TiO2 inter-layer maintains 51% of its initial PCE after storage under dark ambient conditions for 700 h without encapsulation, whereas the bilayer OPV without a TiO2 inter-layer did not show any solar cell performance after 200 h under the same conditions.
Bibliographical noteFunding Information:
This research was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT and Future Planning , South Korea and by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry and Energy , South Korea. (Nos. 20133030011330 and 20133030000210 ). We thank Dr. Kris Rathwell for the valuable discussions and Ms. Hee Won Hwang for the XRD measurement.
© 2015 Elsevier B.V.
- Bilayer solar cell
- Charge recombination
- Organic solar cell
- TiO interlayer