The polycrystalline CdS/CdTe thin film solar cell is one of the most important photovoltaic devices for cost-effective generation of solar electricity for terrestrial applications. A typical superstrate structure of CdTe solar cell has been studied through current-voltage (J-V) and secondary ion mass spectroscopy (SIMS) measurements. A close correlation between quality of interphases and its photovoltaic efficiency was determined. It was found an improvement of open circuit voltage (VOC) and efficiency associated to CdS and CdTe thermal treatments, and a reduction of diffusion of S and Cd into CdTe and CdS respectively. An efficiency of 12% has been reached on solar cells with a Te and ZnTe interlayer as part of the back contact. Low diffusion of Cu along absorbent material was observed when Te and ZnTe was used creating a stable back contact along the time. Diffusion and intermixing at each junction SnO2:F/CdS, CdS/CdTe and CdTe/Te or ZnTe/Cu/Au was found, establishing limit values of element diffusion along CdTe solar cells.

CdTe semiconductor is an absorbent material used in “tandem” photovoltaic solar cells. This material is commonly deposited by thermal evaporation presenting electrical resistivity values about of 105 Ω·cm to 109 Ω·cm. CdTe is applied in thin solar cells as p-type layer which is in contact with metal back electrode in solar cells. In the CdTe/metal junction a Schottky barrier exits; and small number of charge carriers have enough energy to get over the barrier and cross to the metal back contact. To solve part of this problem, nanostructured Te thin films were used as intermediate layers between CdTe and metal contact. Te layers whit different physical properties were deposited on CdS/CdTe structure by thermal evaporation employing different growth parameters. The electrical parameters of CdTe solar cells were influenced by p+ Te regions. p+ Te regions used as intermediate layer with large deposition time increases the FF and VOC values from 30% to 60% and 560 mV to 730 mV respectively. Also, the electrical resistivity is reduced from 106 Ω·cm to 103 Ω·cm. In this sense, Te region implemented as nanostructure allows to reduce the series resistance from 99 Ω to 20 Ω and increases the shunt resistance from 1445 Ω to 4424 Ω ; Te region as thin films demonstrated not be adequate.

Abstract CdTe thin films solar cells are currently produced using a layer sequence of glass/FTO/CdS/CdTe/metal contact (Cu/Ag), these films are deposited by two different techniques, chemical bath deposition (CBD) and close space vapour transport (CSVT). In order to reach reasonable conversion efficiencies, the device has to be thermally treated in a hydrated-CdCl2 atmosphere. This study was carried out using X-ray diffraction (XRD), photoluminescence, SEM-EDS, four probe method and SIMS profiling of CdTe. These analyses confirm the presence of hydrated CdCl2 and CdTe phases on CdTe surface and shown a good recrystallization morphology helping to the carriers mobility along the structure. Using the thermal treatment was possible to reduce the resistivity of CdTe thin film; it is a result to the Cl migration along the CdTe solar cell structure, reducing the defects between CdS and CdTe thin films. A strong CdTe thin film recrystallization was observed by the implementation of a hydrated-CdCl2 treatment doing to this a good candidate to CdTe solar cells process.

CdS polycrystalline thin films have been used as window layer in solar cells; the optical and crystalline quality of the CdS-partner plays an important role in the photovoltaic device performance. CdS thin films were deposited by using Chemical Bath Deposition (CBD). The SnO2 :F substrates used were chemically treated with HCl (0.1M) and others were thermally annealed in different atmospheres (Ar y O2). The physical properties of CdS thin films were influenced by the HCl treatment, position, size and the substrates movement inside the reaction beaker. The CdS samples were deposited in áreas of 4 cm², 50 cm² and 100 cm². Finaly CdS thin films with thickness of 35-300 nm with good optical and crystalline quality on a uniform morphology were obtained. Transmittance values were obtained for all samples about 85-90% with an average of gap energy of 2.5 eV.

Las películas delgadas policristalinas de CdS han sido usadas como el material ventana en celdas solares; la calidad (óptica y cristalina de la película delgada de CdS juega un papel muy importante en el desempeño del dispositivo fotovoltaíco. Películas delgadas de CdS fueron depositadas utilizando la técnica de bario químico (DBQ). Los substratos de SnO2 :F utilizados fueron tratados químicamente con HCl (0.1M) y algunos otros fueron térmicamente recocidos en diferentes atmosferas (Ar and O2). Observamos que las propiedades físicas de las películas delgadas de CdS se ven influenciadas por el tratamiento con HCl, la posición, el tamaño y el movimiento del substrato dentro del vaso reactor. Las muestras de CdS se depositaron en áreas de 4 cm², 50 cm² and 100 cm². Finalmente se obtivieron películas delgadas con espesores de 35 - 300 nm con buena calidad óptica y cristalina en una morfología uniforme. Los Los valores de transmitancia en las muestras obtenidas se encuentran entre un 85 y 90% con una brecha prohibida de energía promedio de 2.5 eV.

Polycrystalline Cu(In,Ga)Se2 (CIGS) solar cells are attractive because low cost techniques can be used to obtain high efficiency thin film photovoltaic devices. Several research groups around the world have developed CIGS/CdS solar cells with efficiencies larger than 15% [1] using evaporation, making it an attractive and reliable technique for thin film deposition. Our PVD system is provided with MBE-type Knudsen cells to deposit CIGS thin films on glass/Molibdenum (Mo) substrates. The deposition conditions for each metal source have been established by doing a deposition profile of temperature data vs. growth rate by co-evaporation to obtain CIGS thin film for solar cells. Characterization of the co-evaporated CIGS thin films was performed by X-ray diffraction (X-RD), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) techniques. Good quality polycrystalline films were obtained as shown by X-RD patterns. SEM micrographs show films having a very uniform appearance with large grain sizes (~1 µm). Photoluminescence (PL) studies on CIGS samples with different Ga and Cu concentrations (Ga/Ga+In) = 0.25 and 0.34 and (Cu/In+Ga) = 0.83, 0.88 and 0.94) have been performed. The EDS results have shown that is possible to control very precisely the CIGS thin film composition using these Knudsen cells. Film thicknesses of ~3-4 µm, were measured with an Ambios profilemeter XP 100 stylus type. A conversion efficiency of 10.9 % has been achieved for solar cells made from the co-evaporated absorbers.