The study of zinc oxide, tin oxide and zinc-tin oxide as anti-reflective coating silicon solar cells / Nuraini Binti Abdullah

Faculty of Manufacturing & Mechatronics Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang - 2025

Includes bibliographical references

Solar energy is one of the sources of renewable energy that is free and infinite source of energy that can be converted into usable power for various applications. The conversion of sunlight into useful electrical energy by electrical instrument is called photovoltaic. The efficiency of a solar cell is mainly affected by the reflection of light from its front surface. The antireflective coatings (ARC) that covered the top of the solar cell surface can reduce the reflection coefficient. In this research work, the SnO2, ZnO and ZnO-SnO2 thin film were deposited on p-type (100) Si by using thermal evaporation and thermal oxidation method by controlling the growth parameter. The structural and optical properties of SnO2, ZnO and ZnO-SnO2 were studied as antireflective coatings (ARC) that was very important to reduce the reflection of light of solar cell. ZnO, SnO2 and ZnO-SnO2 were successfully deposited on Si (100) substrate by thermal evaporation method and thermal oxidation. The base pressure of 3.6 x 10-5 mbar, 5 V of voltage and 60 mA current was used during. The XRD pattern shows that the oxidation of SnO2, ZnO and ZnO-SnO2 at oxidation temperature 100 oC, not completely oxidized because the peaks corresponding to other phases still appears at this temperature. The SnO2 was started to oxidize at growth temperature 300 oC and fully oxidized at oxidation temperature 500 oC. As an optimization fabrication of thin film ARC Si solar cell, the desired thickness of ZnO and SnO2 was controlled by measured mass of each respective material and oxidized at 700 oC for 1h that were confirmed by cross section by field emission scanning electron microscope (FESEM). For the fabrication of photovoltaic (PV) cells, an n-type emitter is deposited using a solution of phosphoric acid and 2-butanol via spin coating method and diffused at 950 oC for 20 minutes into the bare Si (for reference) and thin film ARC Si solar cell for each thin film material. Surface morphological, optical and electrical properties of the thin film ARC Si solar cells for each material were investigated using FESEM, EDX, XRD, AFM, UV-VIS-NIR spectrophotometer and Hall Effect measurement system. Bare Si wafer demonstrates total reflection (R%) of around 35%-40% within 300-1100 nm wavelength region and electron mobility (μe) of 32.9 cm2/Vs and carrier concentration ne is 1.84 x 1015 cm-3. From the optimized fabrication of thin film ARC Si, the lowest R% of 10.3% is achieved from the ZnO-SnO2 0.04 g / 0.01 g ARC thin film on Si substrate. The optimized thin film ARC Si solar cell exhibits root mean square (RMS) surface roughness of 36.5 nm, electron mobility (μe) of 22.2 cm2/Vs, carrier concentration (ne) of 1.44 x 1017 cm-3. The refractive index of SnO2, ZnO and ZnO-SnO2 ARC on Si were calculated and the results obtained were in range 1.97 to 2.29 as compared to bare c-Si which is 3.89. The optical band gap was estimated by using Tauc plot, the results of SnO2, ZnO and ZnO-SnO2 ARC thin film on silicon were obtained in range 2.16 to 2.89 eV as compared to c-Si which is 1.27 eV. The PV cells are characterized by a white light emitting diode (LED) solar simulator at room temperature (~25 oC) with an input illumination power of 45 mW/cm2. The bare Si PV cell demonstrates average conversion efficiency (ηavg) of 3.01%. While for optimized thin film ARC Si of ZnO produced ηavg of 3.38%. The best performance is obtained by ARC Si of ZnO-SnO2 which exhibits ηavg of 4.60%.