Low cost methods for fabricating the dye-sensitized solar cells (DSSCs) and CdTe solar cells are presented, including rapid dye sensitizing, counter and working electrode processing, window and buffer layer processing, post-deposition treatment and the formation of new materials for counter electrodes and low sheet resistance back contact. The study contains fundamental characterization data, technical relationships and device results. The first study focused on a novel rapid or fast dyeing and co-sensitizing method for DSSCs using N7 l 9 and SQ 1-CDCA dyes. A new method to measure the absorption and desorption of dye during the co-sensitizing with fast and passive dyeing was developed in this study. The behaviour of the dyes absorbed and desorbed from the TiO₂ photoelectrode was observed and the dominant dye which strongly absorbed and desorbed was also identified. The technical issues such as the fabrication and pumping technique and the also the effect of the Surlyn gasket which provides a cavity between the TiO₂ photoelectrode and Pt counter electrode was also discussed in this study. The performance of DSSC devices was also measured and compared to the various ratios of dye and with different Sun levels during the co-sensitization by fast and passive dyeing.
A new technique of fabricating the CdTe by doctor blading was also introduced in this study. CdS was used as a window material for this study using a modified
CBD method. The issues of these two materials during the deposition and
fabrication were also identified. The main issue for the CdS-CBD was the porosity of the film which shorting the current of devices. The main issue identified for CdTe film using this doctor blading technique was the film thickness due to the large particle sizes of CdTe powder used. The device performances of doctor bladed CdTe deposited on CBd-CdS were compared to MOCVD-deposited CdTe with CBD-CdS. Low efficiencies were measured due to the materials issue mentioned above.
ln this study, the potential of cobalt sulfide as a catalyst for DSSC and nickel as a
back contact for PV devices were also explored. Modified methods for depositing
cobalt sulfide using CBD method or electrochemistry were compared and
developed. A simple elctroless method to deposit the nickel as a potential back
contact for CdTe devices was also developed and the film properties such as
thickness and resistivity were also measured.
This thesis is arranged into five Chapters. Chapter one gives an introduction by
describing the background and the purpose of the study as well as a literature
review which describes the major issues of renewable energy, CdTe/CdS thin
films solar cells, dye-sensitized solar cells and transparent conducting oxides.
Chapter 2 explains the procedures in the development and fabrication techniques of DSSCs and CdTe/CdS solar cells, a new method for co-sensitizing of DSSCs including absorption and desorption studies, doctor blading techniques for CdTe films and describes the analytical techniques for analyzing the structure and properties of the materials and devices.
Chapter 3 discusses a new technique for fabricating low cost DSSCs. This chapter starts with a sub-chapter on cobalt sulfide deposition procedures and the potential of this material as the catalyst for DSSC counter electrodes. The behaviour of dyes such as absorption and desorption including the mass, number of moles and number of molecules was also discussed with regards to fast co-sensitization. The performance of devices by fast and passive dyeing was also compared and explained in this chapter. The issues and the limitations of the techniques and dyes are also considered.
The development of CdTe/CdS thin film solar cells is introduced in Chapter 4.
This Chapter starts with the background of the study and is followed by a subchapter on electroless nickel deposition. The characterization of CdS and CdTe layers using XRD, SEM-EDAX and AFM are also described. The device
performances of the CdTe deposited by doctor blading or MOCVD onto CdSiv
CBD are also compared and discussed. The CdTe and CdS problems during
fabrication were also highlighted in this chapter.
Finally, Chapter 5 concludes and summarizes all the results gained from the
studies in this work. The limitations along with the recommendations for future
studies are also suggested in this chapter.