ENGINEERING THE MICROSTRUCTURE AND CHEMISTRY OF BOTH QUANTUM DOTS AND PHOTOANODES IN QUANTUM-DOT SENSITIZED SOLAR CELLS FOR HIGH POWER CONVERSION EFFICIENCY

摘要

Quantum dot-sensitized solar cells (QDSCs) as a derivative of dye-sensitized solar cells (DSCs) have attracted considerable attention and been regarded as a promising alternative to conventional solid-state semiconductor solar cells. QDSCs are relatively cost-effective and easy to manufacture, and furthermore, compared to organic dyes, narrow band gap semiconductor QDs possess multiple extraordinary optical and electrical properties in terms of (1) tunable band gap across a wide energy range, (2) strong light absorption, (3) high stability against oxidative deterioration, (4) high extinction coefficients, and (5) large intrinsic dipole moment facilitating charge separation. A high theoretical photovoltaic conversion efficiency up to 44% in view of the multiple excitation generation (MEG) effect, beyond the traditional Shockley and Queisser limit of 32% for semiconductor solar cell, has encouraged people to develop QDSCs with the use of CdS, CdSe, CdTe, PbS, and Ag2S QDs, as sensitizers for light harvesting. Furthermore, some co-sensitization systems, especially the combination of CdS and CdSe QDs, have also been widely studied. However, the power conversion efficiency of these QDSCs, typically with the efficiency of 1-5%, still lags far behind ~ 12% of DSCs. Obviously efforts are needed to get a better fundamental understanding so as to develop the materials and nano/micro-structures for the QDSCs to achieve high power conversion efficiency and explore the full potential of the QDSCs. Two approaches are explored to improve the power conversion efficiency: (1) manipulation of the nano and microstructufes and surface chemistry of the wide bandgap semiconductor oxide photoanodes with efficient quantum dots deposition and desirable internal light scattering, and (2) alignment and controlled variation of the bandgaps of quantum dots through ion exchange.