Nano-Si kolon yapılarının güneş pili uygulamarı için tasarlanıp, üretilip, karakterize edilmesi

Energy demand has had an increasing growth since industrial revolution at the end of the 19th century. One reason for growth of energy demand is increasing world population. It has doubled in last 40 years. The second reasons is rising in life standarts. Generation, transmission and distribution of electricity were considered as a strategic management for a lot of country. However nuclear accidents in Chernobyl and Fukushima, global waraming problem and carbon emission, direct a lot of countries to the renewable energy sources. Germany is the leader country in solar energy investments and has a national target to obtain 50% of its energy consumption from renewable energy sources. Investments and researches have been increasing in this field in last two decades due to the abundance of silicon in the nature, sun is an infinite source, less cost and less material consumption through cutting-edge material deposition techniques. Solar cells contain p-n junction which can be conceived as two type of semiconductors have a surface in common. In this system majority careers in n type (electrons) begin to diffuse into p region and recombine with holes. Similarly, majority careers from p type semiconductor (holes) begin to diffuse into n region and recombine with electrons. Therefore depletion layer, where no charge careers exist, occured near the junction. When this system expose to the light minority careers from both sides cross through depletion zone and generete a current. First generation solar cells are based on simple p-n junction. The second generation cells are made of doped thin films typically Cadmium Telluride (CdTe), Copper Indium Gallium Selenide (CIGS), Copper Zink Tin Sulfide (CZTS). These materials have ideal bandgap for solar cells however their scarcity and cost limit the use. The third generation solar cells are made of quantum dots. QDs are semiconductor particles and their bandgap can be tunable. Through this property this structures are able to harvest wide range of solar radiation. The fourth generation of solar cells are based on hybrid inorganic crystals within polymer molecules. In this thesis n type amorphous silicon columnar structures were deposited through glancing angle deposition technique in different geometries. Cross-sectional and top-view SEM images show that these structures have more porous structures compared to flat surface. As a result of this colomnar structures possess less reflectivity according to the UV-VIS spectroscopy which means these structures absorb more photons compared to flat surface. This is an important factor to increase efficiency of solar cells by increasing light trapping. Porous surface have also changed the surface hydrophobicity. According to the contact angle measurements flat silicon have 98o while columnar structures have 71o and 61o. This is important both for increase light trapping and better distribution of PEDOT:PSS hole conductor polymer layer on the surface. AFM images scanned in 1μmx1μm area also shows that columnar structures exhibit more surface roughness compared to flat surfaces. PEDOT:PSS was covered using spin coating method. First it was dropped onto surface and wait for 1min. then it was spin coated with 2000rpm twice. UV-VIS spectroscopy shows that PEDOT:PSS is highly transparent and suitable for solar cell applications. Also SEM images of PEDOT covered silicon structures show that columnar structures have larger p-n junction interface area due to both porous surface and hydrophilicity . Another method to increase efficiency of such structures is to create different geometries by different methods such as chemical vapor deposition and etching to increase surface porosity. We can also use mono-crystalline materials instead of poly-crystalline and amorphous materials to prevent dangling bonds which can cause current leakage. Also surface treatment techniques such as oxidation and hydrogen terminating can be apply to the absorber layer surface. For bottom up methods cooling down the substrate provides better distrubition of columnar structures. Quantum dots and carbon nanotubes can be added to absorber layer to reduce reflectivity and increase absorption. Some chemicals can be added to PEDOT:PSS polymer to increase hole concentration.