Preparation Of Single Crystal Silicon Wafers And Lead Sulfide Films

It has been known that solar cells based on Si take main share in the current photovoltaic market. Surface texturing of monocrystalline silicon is a effective approach to reduce the light loss and improve the conversion efficiency for solar cells. In order to lower the cost and enhance efficiency, people have been looking for new semiconductor photovoltaic materials. PbS is an important direct band gap ?Eg= 0.41 eV? IV-VI p-type semiconductor. It has a potential application in solar cells, infrared detector devices, sensors, etc.. Surface texturing of monocrystalline silicon wafer and PbS films deposition were studied. The results are as follows:We studied the effect of different additives ?methyl alcohol, ethanol, isopropanol ?IPA?, ethanediol,1,2-propylene glycol? on the morphology and reflectivity of the pyramidal textures. More uniform pyramidal structure, the right pyramid size, less collapsed pyramid were obtained when monohydric alcohol ?methyl alcohol, ethanol, IPA? were used as additive. Inhomogeneous pyramidal structure, many unformed pyramid were obtained when diols ?ethylene glycol,1,2-propylene glycol? were used as the additive. This is because monoalcohol has better antifoaming effect than diol. The reflectivity of pyramidal texture obtained by monohydric alcohol was lower than that of the diols. Pyramidal texture with uniform size, medium size ?3-5 ?m?, and lowest reflectivity of about 11.8% were obtained when IPA was used as additive.We studied the influence of pre-annealing on texturing of crystalline silicon. Pyramidal texture with uniform size, bigger size ?5-7 ?m?, lower reflectivity were obtained by pre-annealing. The defect density of monocrystalline silicon is reduced. Thus, uniform structure, larger pyramids are easily formed. The size of the pyramid increases from 4-6 ?m to 6-8 ?m as pre-annealing temperature increases from 200? to 500? for 20 min pre-annealing. Reflectivity of the wafer surface is about 11.7% without pre-annealing process. Reflectivity of the wafer surface is reduced from 10% to 9% as pre-annealing temperature increases from 200? to 400? for 20 min pre-annealing. However, Reflectivity increases to 10.4% with the pre-annealing temperature increases to 500?. For pre-annealing temperature of 400?, pyramidal texture with uniform size, medium size ?5-7 ?m?, lowest reflectivity of-9% was obtained, which is 2.7 percentage lower than that of the texture fabricated by traditional texturing approach. With the pre-annealing temperature increases from 200? to 500? for 10 min pre-annealing, the reflectivity has a small change around 11%. For pre-annealing temperature of 400?, the lowest reflectivity of-10.7% was obtained.PbS thin films were deposited via chemical bath deposition ?CBD?. We studied the influence of depositing time on structural and optical properties of the PbS films. The uniform, dense, and very adherent PbS films were obtained. As deposition time increases from 25 min to 300 min, the crystallinity of PbS film gets better. The transmittance over 1000 nm grows higher and the transmittance under 1000 nm becomes lower.Cu-doped PbS thin films were deposited via chemical bath deposition ?CBD?. We studied the effect of Cu doping concentration on the structural, optical, electrical properties of PbS films. The average crystallite size of Cu-doped PbS film is smaller than the un-doped PbS film. The crystallite size of un-doped PbS film is 45.5 nm. As Cu doping concentration increases from 0 to 6.3 at.%, the crystallite size of PbS films increases from 27.4 to 44.7 nm. As the Cu doping concentration increases from 6.3 at.% to7.9 at.%, the crystallite size of PbS film reduces to 42.9 nm. Cu doping leads to larger band gap. The band gap of un-doped PbS film is 1.14 eV. As the Cu doping concentration increases from 0 to 6.3 at.%, the band gap of PbS films decreases from 1.28 eV to 1.16 eV. As the Cu doping concentration increases from 6.3 at.% to 7.9 at.%, the band gap of PbS film increases to 1.18 eV. Cu doping leads to higher carrier concentration. As the Cu doping concentration increases from 0 to 6.3 at.%, the carrier concentration of PbS films increases from 3.49×1015 to 4.26×1018 cm^-3. We think that the substitution of Cu ions for Pb ions could induce more vacancies. As the Cu doping concentration increases from 6.3 at.% to 7.9 at.%, the carrier concentration of PbS film reduces to 4.05×1017 cm^-3. The carrier mobility exhibits a reverse trend from 110.9 cm²/V s to 7.1 cm²/V s. Cu doping leads to lower resistivity. As the Cu doping concentration increases from 0 to 6.3 at.%, the resistivity of PbS films decreases from 16 to 0.15?·cm. The resistivity is smaller than previously reported resistivity of PbS films. As the Cu doping concentration increases from 6.3 at.% to 7.9 at.%, the resistivity increases to 0.15?·cm.