Development of Polymer Solar cells with Organic-Inorganic Sandwiched Structures through Solution Processing

• Main Authors: Jing-Shun Huang, 黃敬舜
• Other Authors: Ching-Fuh Lin
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/76343317826375454940

博士 === 臺灣大學 === 光電工程學研究所 === 98 === As the search for alternative sources of energy other than fossil fuels continues to expand, photovoltaic technology (direct conversion of solar energy into electrical energy) has been identified as one of the promising technologies. Solar cells based on blends of conjugated polymers and fullerene derivatives have recently attracted significant attention due to their great promise for the realization of printable, portable, flexible, and low-cost renewable energy sources. However, it is not easy to precisely control the nanoscale morphology of photoactive layer which seriously affects the carrier transport. In addition, control of the charge transport at organic-electrode or organic-inorganic interface is also challenging in polymer-based solar cells (PSCs). Quality of the electrode interface is also critical for the PSC stability. This dissertation focuses on the development of PSCs with organic-inorganic sandwiched structures (organic photoactive layer sandwiched between two inorganic semiconductor layers), which exhibit high efficiency, air-stability, and low cost. First, environmentally friendly ZnO nanorod arrays grown in an aqueous solution are presented. At a low annealing temperature (130 ℃), the ZnO nanorod arrays align very vertically with rod diameter of 50 nm and rod-to-rod spacing of 10-50 nm. This provides a solution-based route to the fabrication of low-cost organic-inorganic photovoltaic devices with highly oriented ZnO nanorod arrays. In order to achieve better exciton dissociation and charge transport, three types of interfacial modifications are demonstrated in the PSCs hybridized the ZnO nanorod arrays. The addition of PCBM clusters can enhance the phase separation and optical absorption. Inserting TiO2 nanoparticles leads to a formation of double heterojunction, providing efficient exciton dissociation and charge transfer. The insertion of V2O5 nanopowder can suppress the leakage current and enhance the absorption. With the PCBM clusters, TiO2 nanoparticles, and V2O5 nanopowder, the power conversion efficiencies (PCEs) can be improved from 2.3% to 3.2%, 4%, and 3.6%, respectively. Moreover, in order to develop the organic-inorganic sandwiched structures, four kinds of metal oxides, NiO, V2O5, WO3, and CuO, as anodic modifications are explored in inverted PSCs with ZnO film at cathode as hole blocker. NiO, V2O5, and CuO are beneficial for hole transport. NiO and V2O5 further have high barriers against electrons, thereby suppressing leakage current at the anode. WO3 is beneficial for the electron extraction from Ag into P3HT. With one of these oxides, PCE can be improved from ~3% to ~3.7%. In addition to the individual oxides, WO3-V2O5 mixed oxides as anodic modification are also studied because they are complementary. P3HT:PCBM and PV2000 are used as the photoactive layer, respectively. With the sandwiched structure consisting of mixed oxides and ZnO film, the leakage current can be suppressed. The optical absorption and quantum efficiency are also improved by the mixed oxides. Additionally, the mixed oxides are relatively stable in air, so they can protect photoactive layer therein from the oxygen or water damaging and thus improve device durability. As a result, the PCEs are improved to 4.16% for the P3HT:PCBM system and to 5.13% for the PV2000 system, respectively. Furthermore, these interfacial modifications and the sandwiched structures are all fabricated by solution approaches. Compared to the vacuum-deposited techniques, these approaches are simple, expeditious, and effective. They are also advantageous for potential applications to mass production of various large-area printed electronics and photonics with a very low cost. In addition to the low cost, the solution process provides the convenience of mixing different kinds of oxides in a desired ratio, which cannot be easily achieved by thermal co-evaporation due to the different boiling points of oxides.