D. Kindl

Preparation and characterization of CdS/CdTe thin film solar cells

Abstract Thin film n-CdS/p-CdTe heterojunctions for solar cells were prepared by chemical deposition of CdS and electrodeposition of CdTe layers. No chlorine was intentionally put into the deposition solution for CdTe preparation (the A samples), whereas chloride ions were added in the case of the B samples. No post-depobition treatment with CdCl 2 followed. The structure and morphology of the cells were analyzed using X-ray diffraction and scanning electron microscopy, The photovoltaic properties were tested using illuminated current-voltage characteristics. The relationship between the structure and morphology of the CdTe layers and the efficiency of the cells was found, and it was confirmed that the presence of chloride ions was essential to achieve an efficiency of 9.4%. The contactless pholovoltage (CPV) method was used to measure the minority carrier diffusion length in CdTe. Values of the diffusion length and some other parameters of the cells were deduced by fitting the theoretical curve of the CPV spectral response to the experiment.

Diffusion length in CdTe by measurement of photovoltage spectra in CdS/CdTe solar cells

Modified method of surface photovoltage (SPV), spectral response measurement, and constant photocurrent method (CPM) were applied to thin film CdS/CdTe solar cells with the aim of finding diffusion length of minority carriers (L) in the CdTe material. The SPV signal was theoretically calculated without constraints of absorption coefficients for the incident radiation and thickness of the sample assuming one space charge region (SCR) located on the CdS/CdTe interface. In addition to the diffusion length, the SPV is a function of the surface recombination velocity and the parameters of the SCR, which complicates the evaluation. Illuminating the back side of the solar cell (without ohmic contact) we obtain a photovoltage spectrum predominantly influenced by the diffusion length. On the other hand, the standard measurement using light penetrating from the CdS side strongly depends on the thickness of the SCR. The small signal approximation model presented here successfully explains both measured spectra and p...

Contactless photovoltage method for measurement of diffusion length of minority carriers in solar cells

Contactless photovoltage method is presented as a generalization of conventional surface photovoltage investigation of semiconductor parameters. Existence of two space charge regions causing two signals of opposite sign was taken into account and calculated photovoltage was compared with experimental data. The method has been used for evaluation of parameters of silicon solar cells.

Improved photovoltaic method for measurement of minority carrier diffusion length applied to silicon solar cells

Abstract The photovoltage spectrum measured on back illuminated silicon solar cells of the (passivated emitor solar cell) (PESC) type without original bottom ohmic electrode is evaluated with the aim to find the diffusion length of minority carriers in bulk of the absorber ( L ). Two junctions, namely pn + junction of the cell and that spontaneously created on the free surface generally exist in such samples. They give rise to two signals of opposite signs with one point of exact compensation. Six parameters (including L ) are needed to characterize the spectrum. Special simple arrangement removes influence of spontaneously created junction on the free surface, which, in this way, reduces the number of parameters needed for fitting to three and enhances reliability of the measurement.

Some properties of electrodeposited CdTe thin layers

Polycrystalline CdTe layers have been deposited cathodically on nickel substrates from an aqueous solution of CdSO4 and TeO2. The structure of the deposits was studied by means of X-ray diffraction. Measurements of current-voltage and capitance-voltage characteristics and spectral dependence of the short-circuit current of a Au-CdTe Schottky diode prepared on the basis of these layers, were performed. Parameters as height of both Schottky and intergranular barrier, impurity concentration in the bulk of the grains and minority carriers effective diffusion length were determined.