Research On The Effect Of Sulfuration Condition To Cu₂ZnSnS₄Thin Film’s Structural And Optical Properties

At present, solar energy is regarded as the most promising sustainable energy as its advantageslike abundant amount and environmentally friendly. Solar cell is a kind of device converting solarpower to electricity. In all compound solar cells, CIGS(Cu2InGaSe4) has the highest efficiency, whichis very close to that of multicrystalline silicon cell. However, CIGS also faces some problems as In isa rare element, so it costs much and is toxic, which makes some limitations for CIGS in use ofcommercial market.In CZTS(Cu2ZnSnS4), Zn and Sn are used to substitute In and Ga in CIGS, and S to replace Se.This could lower the cost and is more environmental friendly. The components of CZTS are in richreserves and has a low price, which brings it possibility to reduce the cost of commercial solar cell inthe future.In this thesis, Zn/Sn/Cu(CZT) metal precursor was prepared by magnetron sputtering andfollowed by sulfuration with two kinds of S source-H2S and S powder to obtain CZTS thin film. Theeffect of sulfuration temperature, time and pretreatment temperature, time on CZTS thin film’sstructure, surface morphology, element ratio and optical property had been studied.When vulcanized with H2S gas, the effect of sulfuration temperature and time had been analyzed.All the samples had (112) preferential growth orientation. When the sulfuration temperature was500℃, the absorption edge of transmittance shifted to long wavelength with longer sulfuration time,while the optical band gap got smaller. The surface of CZTS thin film became dense and flat withhigher sulfuration temperature, but if the temperature was too high, little cracks along grainboundaries appeared. The sample vulcanized under540℃for2h had the largest grains(2μm) and bestcrystallinity. All the optical absorption coefficient of samples prepared in different temperature werelarger than7x104cm-1.When vulcanized with sulfur powder, a pretreatment process was introduced before sulfuration.The effect of different pretreat temperature was studied. All the samples had (112) preferential growthorientation. What’s more important, the pretreatment process could suppress the volatilization of Sn.The reflectance and transmittance of all sample (except200℃pretreated sample in the wavelength700~850nm) were lower than the un-pretreated ones. With the increasing of pretreatment time, theoptical band gap decreased.In an optimal condition for pretreatment process, the effect of sulfuration temperature to CZTS thin film was also studied. All the samples had (112) preferential growth orientation. The results ofRaman test indicated that increasing the sulfuration temperature could improve the crystallinity andgrain size of CZTS thin film.