Date of Award
8-12-2015
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Applied Science
First Advisor
Tar-Pin Chen
Abstract
Silicon nanostructures are good semiconductor materials candidates for replacing bulk silicon because the nanostructure may act as antireflective layer on Si wafer when used in a solar cell device. Silicon nanostructures, whether nanowires or nanorods, has a direct path for charge transport to enhance the efficiency of solar cell devices depends on the nanostructure size and quality. It also has some properties different from that of bulk silicon. For example, the thermal conductivity of silicon nanostructures is lower than that of the bulk silicon because the diameter of the silicon nanowires is smaller in size than the bulk sample. In addition, the Si nanowires provide a large surface area and the band gap of silicon nanowires is tunable through changing the diameter of nanowires. Furthermore, the reflection of incident light on silicon nanowires is lower than that of bulk silicon and thus increases its absorption of the light, which improves the performance of the solar cell device. In this dissertation, we used chemical etching method to grow silicon nanowires on a planar silicon substrate. This simple technique provides a rapid and facile way to grow large-area of nanowires. However, low temperature is needed for growing vertically aligned silicon nanowires. In this method the length of nanowires can be controlled by controlling the growth time, on the other hand the diameter of nanowires can't be control through controlling the growth time. By using this technique we have succeeded in growing n-type and p-type nanowires on planer silicon substrates to build our solar cells devices in low cost. We have fabricated branched heterojunction structures by growing horizontal ZnO nanowires (ZnO-NWs) on vertical Si nanowires (Si-NWs). The ZnO nanowires were grown in solution by an electrochemical process. Structure and electrical properties of the branched nanowires were studied by SEM, XDR, and electrical measurements. The SEM images show that the 3-D ZnO nanowires branches were successfully grown on the branched Si nanowires. Due to its light trapping effect this special structure may have good applications in photovoltaic devices. Solar cells based on this branched structure were also fabricated and tested. We found that their cell performance depends on both the length of the Si nanowires and the ZnO nanowires and the thickness of ZnO seed layer. A Core-Shell Si/CdS nanowires heterojunction structures has been successful fabrication at low cost by preparing n type cadmium sulfite nanoparticles (CdS-NPs) on a large area of vertically alighted p type Si nanowires (Si-NWs). The CdS nanoparticles were fabricated by chemical bath deposition (CBD), while the Si wafer was etched in chemical solution to obtain Si nanowires. SEM images show that the 2-D CdS nanoparticles are well adhesive on the Si nanowires. The Optical properties for several different thicknesses CdS nanoparticles thin films fabricated on glass slide and on Si nanowires were studied by measuring their UV-Visible absorption and Raman spectra. The structure of CdS nanoparticles thin film was investigated by XRD. We deposited Al doped ZnO (AZO) film on CdS-NPs/Si-NWs heterojunction as electrode to improve the performance of the heterojunction devices. We have also studied the performance of the solar cell before and after depositing AZO, its dependence on the length of Si nanowires, and on the thickness of the CdS nanoparticles layers. The power conversion efficiency after deposited AZO on the heterostructure device was 10 times higher than before depositing AZO. Furthermore, we grew thin graphene film by chemical vapor deposition on Cu foil. This thin graphene film has good transparency, high conductivity and strong suitable for the use as electrode on top of the solar cell devices. The optical measurements on graphene film show that the thickness of the film increased with increasing the growth times. A transparency graphene film was transfer to ZnO-NWs/Si-NW and CdS-NPs/Si-NWs heterostructures devices. The graphene film improved the performance of heterostructures devices through electrical measurements. The power conversion efficiency of the devices with graphene film was 2 times higher than that of the power conversion efficiency without graphene film.
Recommended Citation
AL-Hilo, Alaa Abdul-Halim, "Fabrication and Characterization Silicon Nanowires Based Heterostructure Solar Cell Devices" (2015). Theses and Dissertations. 593.
https://research.ualr.edu/etd/593
