The Research Of The Preparation,Selenizated And Photoelectrical Mechanism Of CuInSe₂ Thin Film Solar Cell Prepared By Whole Magnetron Sputtering

Human’s demand for new energy resourses made Cu In Se₂（CIS） solar cell require more and more high performance, so the research and development of new low cost and low energy consumption way of selenium method had become the inevitable trend of industrialization application of CIS thin film solar cells. It is also very important to broaden the application field and market potential of thin-film solar cells. In this paper CIS thin film solar cell were deposited by whole magnetron sputtering. Some selenizing processes and parameters such as selenizing temperature, selenizing substrate material, selenizing pressure,selenizing power, annealing temperature and selenizing time were optimized and controlled.The change law of microstructure, morphology, composition, growth orientation, electrical property, optical property and photo-electrical property of CIS films on these selenizing processes were studied. The selenide and photoelectrical mechanism relating to microstructure and property of CIS films were analyzed.In the research of selenizing processes of Cu In Se₂ films, different selenizing processes on the control and influence of the phase transformation, surface morphologies, electrical and optical properties of CIS films were analyzed. Studies have shown that:（1） Increasing selenizing temperature but not exceeding 200℃ was beneficial to form the preferred orientation of chalcopyrite phase and it suppress the sphalerite phase. With the increase of selenizing temperature, the grain shape of the films could be changed from particle-like to plate-like. The roughness of the films decreased firstly and then increased with the increase of selenizing temperatures. Therefore, in all heating process the film at 200 ℃,low-temperature process had the best electrical and optical property;（2） The FTO（Sn O2:F）and Cu-sub films all showed good quality of thin film. Two-phase structures including chalcopyrite and sphalerite phase were existed in the FTO-sub film and it showed better optical performance, while single-phase of chalcopyrite structure was formed in Cu-sub films and it showed better conductivity performance;（3） CIS particles of better crystallinity and larger grain size could be formed on low-temperature annealing processes not exceeding 250℃. Also, it could avoid the desorption of In/Se and phase transformation of CIS;（4） With the increase of selenizing time, the diffraction peak intensity of two phase structures in CIS thin film increased, which indicated that a significant increase in the grain sizes and the films showed better electrical conductivity and optical performance;（5） At lower selenizing pressure（0.5 Pa）, clear boundary and uniform distribution of particles occurred in CIS film. However, higher selenizing power（150W） could promote the phase change from In2Se3 and Cu2-x Se phase to CIS ternary phase. Therefore, the low pressure and high power process all showed the better electrical and optical property.According to the analysis of the structures and surface morphologies of the CIS thin films, the selenizing mechanism of CIS thin films was studied, and the six selenide models of the CIS films were proposed. Studies of selenizing mechanism have shown that: Threeselenide stages were occurred in the selenizing heating process: selenium of Se stage occurred at low temperature, selenium of Cu stage occurred at middle temperature, ternary selenium stage occurred at high temperature. Different selenium mechanism of annealing process could be achieved through three models, slow selenium occurred at low temperature,rapid selenium occurred at middle temperature, non-selenium model occurred at high temperature. Different selenium mechanisms on selenizing substrate materials could be achieved in three models, full selenium model occurred on FTO and Cu-sub film, partial selenium occurred on Steel and Al-sub films, and non-selenium model occurred on Si-sub film. Different selenium mechanisms at different selenizing time could be achieved in three models, dispersed selenide model in short time, concentrated selenide model in middle time and long-term accumulated selenide model in long time. Different selenium mechanisms at different selenizing pressure could be achieved in three models, Intensive attraction model occurred at low pressure, sparse mosaic model occurred at middling pressure and isolated rejection model occurred at high pressure. Different selenium mechanisms at different selenizing power could be achieved in three models, small-angle bombard model occurred at low power, reflection then packing model occurred at middling power and large-angle incorporation model occurred at high power.According to the analysis of the structures, morphologies and selenide mechanism of the CIS thin films, the photoelectric properties and transport mechanism of CIS thin films were studied, and six photoelectric transport models of the CIS films were proposed.Studies of photoelectrical properties have shown that: The conversion efficiency and short circuit current density of batteries increased firstly and then decreased with the increase of substrate temperature. The conversion efficiency of Cu-sub CIS thin-film batteries was bigger compared to other substrate and its short circuit current density was biggest in all cells. Conversion efficiency and short circuit current density of the annealing treating batteries all increased compared with those with no annealing processes. With the increase of annealing temperature, the conversion efficiency of CIS thin-film batteries showed a trend of increase firstly and then decrease. Low temperature annealing process（200℃） was the optimum process to improve the conversion efficiency of CIS thin-film batteries; With the increase of sputtering time, the conversion efficiency, short circuit current density and the open circuit voltage of CIS thin-film battery all increased; With the increase of sputtering pressure, the open circuit voltage and conversion efficiency of batteries decreases,and short circuit current density showed a trend of increase firstly and then decrease; As the gradual increase of sputtering power, the photoelectric conversion efficiency of the CIS thin-film batteries increased, and the open circuit voltage presented a trend of increase firstly and then decrease, open circuit voltage reached the maximum value when the power increased to 100 W.Studies of photoelectrical transport mechanism have shown that: In the electric field enhancement model by interface adsorption, the particles in the interface between CIS selenide layer and Cd S adsorbed layer adsorbed together, which led to the increase of the junction carrier diffusion channels in the interface layer and accelerate the carrier diffusion speed so as to enhance the strength of the carrier transport electric field on the lowtemperature heating process. In the electric field enhancement model by interface diffusion,the junction carrier in the interface diffusion concentration uniformity was increased on a certain degree and the space charge region was expanded and the space charge was also increased continually so as to enhance the strength of the carrier transport electric field on the low temperature annealing process. In the carrier concentration accumulation model, the function of Cu substrate was similar with Cd S semiconductor layer and the ohmic contact and the barrier layer with the low barrier was formed, which resulted in a large number of carriers from metal back to the space charge region and the increase of carrier diffusion concentration on the side of the Cd S layer. In the carrier quantity accumulation model, as the composite center, the CIS grain boundary decreased and led to increase in the number and life of carrier on the side of CIS layer on the long time process. In the transport channels extruding extended model, the low selenizing pressure made the mutual extrusion between the particles. In this result, the interface in Cd S and CIS layer was formed and the carrier transport channels in the PN junction became to extend with a wavy motion. In the transport channels nail extended model, the high selenizing power made the CIS selenide particle nail into the Cd S layer, so a lot of pit interfaces between CIS and the Cd S layer were formed and the carrier transport channels in the PN junction became bent to extend.