A Study Of The Processes Of Surfaces And Thin Films For Heterojunction Crystalline Silicon Solar Cells And Their Optical Properties

Heterojunction crystalline silicon solar cells are composed of amorphous silicon thin films and crystalline silicon wafers, with the wafers mostly made of N-type silicon. They have features of high open circuit voltage, high efficiency, high stability against long term exposure and temperature increase, and are very promising in the future of photovoltaic industry. The present thesis reports our preliminary studies on preparation and optical properties of wafer surfaces and thin film layers for heterojunction crystalline silicon solar cells. It aims to provide some references for industrial development of heterojunction crystalline silicon solar cells in China.Two step system of texturing, PECVD and magnetron sputtering techniques are used to complete N monocrystalline silicon surface texture, hydrogenated amorphous silicon thin and ITO thin films preparation; and then reflectivity tester, spectroscopic ellipsometer, ultraviolet-visible spectrophotometer, quantum efficiency tester and other means are used to analyze their optical properties, the results show that:1) in20wt%KOH solution under85℃, the n-Si damage layer removed completely when both side of the etching thickness is about20μm and the minority carrier lifetime achieved the optimal; the wafer etching about12μm every side and then in2wt%KOH,5vol%IP A, corrosion about30～35min under70℃, can get better pyramid structure, surface reflectivity can be reduced to11%, the wafer can still get high grade a-Si:H passivation effects after texturing, the quantum efficiency of solar cells in the visible range is more than95%.2) The optical properties of hydrogenated amorphous silicon thin films are very sensitive to its thickness variation. With a-Si:H thin film deposition thickness increases, its refractive index increases, optical absorption coefficient in the near ultraviolet range reduces but in the visible light range increased, forbidden band width is reduced, with p type a-Si:H thin film deposition thickness increases, the refractive index increasing, the optical absorption coefficient in a short period of wavelength decrease but in the visible light range first increase and then decrease, optical band gap width first decrease and then increased; with n type a-Si:H thin film deposition thickness increases, the refractive index increasing. Quantum efficiency shows that the bifacial cells have higher quantum efficiency and performance compared with single-sided cells.3) ITO thin films sputtering on glass substrate at the temperature of250℃, oxygen and argon gas ratio at3/10000,60W for30min, it average optical transmittance on the glass substrate in400-900nm reached80.8%(blank glass is88.1%), the absorption coefficient is approximately5×103cm-1at600nm, the optical band gap width is about3.6eV, the resistivity is about3.82×10-4Ω·cm.