Preparation And Properties Characterization Of PBSE Nanocrystal Film

In this paper, lead selenide (PbSe) films were prepared by RF magnetron sputtering and vacuum evaporation method. The impacts of technological parameter on films crystal structure, surface morphology and optical properties were investigated. The results showed that the (200) preferred orientation and good crystalline quality were observed in most of films. When the substrate temperature exceeding250℃, the preferred orientation of PbSe films changed to (220) plane. The main reason for this change is the microscopic stress increases with increasing temperature. Grains tend to grow in the crystal surface which significantly reduces the microscopic stress of films. So the (220) plane with the smallest micro-strain energy was exposed. The surface morphology of most PbSe films was coverd by spherical particles.But when the substrate temperature exceeds250℃, the particle shape has changed from spherical structure to trilateral. Random lamellar structure appears under the sputtering pressure over2.0Pa.When the thickness increases to93nm and127nm, some particles tend to aggregate and grow up to small worm-like structures. The band gap of PbSe could be adjusted. The band gap of the films mainly contained between1.3-1.6eV which prepared by magnetron sputtering. Those values were significantly less than the band gap of the films (2.05-2.30eV) prepared using a conventional vacuum evaporation technique. The crystalline size and the electric field which comes from charges or barriers within particle boundaries are the major factors for the band gap broadening. The band gap width became narrow when the crystalline size increased. The greater the electric field, the wider the band gap. In general, the optimum conditions for using magnetron sputtering to prepare PbSe thin film: sputtering power100W, sputtering time60min, substrate temperature of200℃(for (200) preferred orientation), sputtering pressure1.0-2.0Pa, distance between the sputtering target is6.5cm, unannealed. The best evaporation time was20min and the optimal annealing temperature is300℃for PbSe film preparation using vacuum evaporation method. Magnetron sputtering method is more suitable to prepare PbSe absorbing layer for use in solar cells.The ITO/CdZnTe/CdS/PbSe/Au solar cell obtained1.06%conversion efficiency. The maximum open circuit voltage (Voc) obtained in experiment was300mV (Sample2), the maximum short circuit current density (Isc) was21.6mA/cm2(Sample5) and the maximum fill factor was25.77%. Thus, there is a considerable room for improvement in the efficiency of solar cells based on PbSe films.