Hybrid Photovoltaic Devices Based On ZnO Nanostructures

As one of the typical semiconductors with a wide and direct band gap, ZnO has a lot of applications such as ultraviolet lasers, ultraviolet photodetectors, and solar cells. ZnO nanostructures of many versatile appearances have many remarkable properties such as big specific surface area and monocrystalline, which are different with other materials. Therefore, ZnO nanostructures become to one of the units of preparing the new nanostructure optoelectronics. In this work, the hybrid photovoltaic devices were demonstrated based on these merits of ZnO nanostructures. The efficency of the soalr cells sensitized with the CdS and PbS quantum dots were increased greatly. The research is outlined as follows.(1) The ZnO nanorods in this work were fabiricated by the electrodeposition method. The ZnO nanorods could be electrodeposited controlled by the seed layer, reaction time and the concentration of the aqueous solution.(2) High spectrum selectivity hybrid ultraviolet photodetector was demonstrated by using electrodeposited ZnO nanorods and poly-N-vinylcarbazole as the electron acceptor and donor, respectively. The high spectrum selectivity hybrid ultraviolet photodetector was obtained based on the particular absoption of ITO glass, ZnO nanorods and poly-N-vinylcarbazole. The photoresponse of the photodetector showed a narrow band centered at 365 nm with a responsibilith of 110 mA/W and with a full width at half maximum of only 26 nm.(3) Poly[2-methoxy-5-(2-ethylhexyloxy-pphenylenevinylene)]/ZnO nanorods hybrid solar cells were demonstrated sensitized by CdS quantum dots prepared by a chemical bath deposition method. A thin ZnO film was adopted to well control the length of the ZnO nanorods and act as a hole-blocking layer. An appropriate coating of the CdS quantum dots on the ZnO nanorods leads to a maximum power conversion efficiency of 0.65%, which was increased 6.5 times compared with the one without using quantum dots. The efficiency of the devices were increased with the quantum of CdS at first and after that decreased with the quantum of CdS. The efficiency reached the maximum value of 0.65% when the CdS quantum dots were coated by 6 cycles.(4) Poly[2-methoxy-5-(2-ethylhexyloxy-pphenylenevinylene)] (MEH-PPV)/ZnO nanorods hybrid solar cells consisting of PbS quantum dots prepared by a chemical bath deposition method were fabricated. An optimum coating of the quantum dots on the ZnO nanorods could strongly improve the performance of the solar cells. And a maximum power conversion efficiency of 0.42% was achieved for the PbS Q quantum dots sensitive solar cell coated by 4 cycles, which was increased almost 5 times compared with the solar cell without using PbS quantum dots. For large clusters the band alignment at the ZnO/PbS interface appears to be unfavorable for carrier transfer due to that the PbS quantum dots are electrically isolated from each other, which result in the decrease of the JSC values and efficiency.