IDEA #19UO4B LOW-TEMPERATURE DEPOSITED CdS AND CdTe THIN FILMS AND THEIR SOLAR CELL APPLICATION

LOW-TEMPERATURE DEPOSITED CdS AND CdTe THIN FILMS AND THEIR SOLAR CELL APPLICATION Description Thin film CdS/CdTe heterojunction devices have been prepared by low-temperature vacuum deposition method. For the device fabrication CdS films of about 90nm and CdTe films of about 5.0 µm thick were subsequently evaporated onto bilayer SnO2 coated Corning 7059 glass substrates. High purity CdS and CdTe powders were used as a source material. Temperature of the substrates was hold at 218K during the evaporation process. The growth rate was controlled by keeping the source temperature within the range of 600-6500C and was about 1.5 nm/s. CdCl2 treatment was carried out using “dry” method where the samples were exposed to CdCl2 vapor at 4000C for 5-7 min. in vacuum chamber in the presence of 100 torr oxygen and 400 torr helium (total pressure was 500 torr). Then the samples were etched in HNO3:H3PO4:H2O mixture (NP etch) in order to convert the CdTe surface to elemental tellurium. For the back contact fabrication the special mixture of graphite paste, CuxTe, and HgTe was deposited and the samples were annealed at 2600C for 25 min. in the presence of inert gas. Silver paste back face electrode was next deposited and the samples were annealed at 1000C in air to complete the devices. Innovative Aspects and Main Advantages Low-temperature evaporation method of CdS and CdTe thin films was found to be one of the successful ways for high efficiency solar cell application. Nearly the same grain sizes and surface morphologies as well as high density of the films provide an optimum intermixing of the components favoring the formation of junction with low concentration of interface states. As a result the high efficiency solar cells with conversion efficiency up to 14 % were fabricated. Our preliminary studies show the possibility of further optimization of the manufacturing technology of CdS/CdTe thin film solar cells by varying physical properties of the device components to achieve maximum efficiency. Areas of application Solar energetic, autonomous power supply for mobile phones, portable computers and radio stations. Stage of development Laboratory tested technology for preparation of CdTe based thin film solar cells. a) b) c) Fig.1. a) SEM photomicrographs of CdS thin films prepared at 218K substrate temperature; b) SEM photomicrographs of CdTe thin films prepared at 218K substrate temperature; c) I-V characteristics of CdS/CdTe thin film solar cell. Contact details Institute of Physics NASA Contact person: Bayramov Ayaz Hidayat oglu Address: 33, H. Javid Avenue AZ1143, Baku, Azerbaijan Tel: (+994 12) 439 1308 E-mail: bayramov@physics.ab.az