Determination of the diode parameters of a-Si and CdTe solar modules using variation of the intensity of illumination: An application Firoz Khan a,b,⇑ , S.N. Singh a , M. Husain b a Physics of Energy Harvesting Division, National Physical Laboratory (CSIR), New Delhi 110 012, India b Department of Physics, Jamia Millia Islamia, New Delhi 110 025, India Received 24 January 2011; received in revised form 7 June 2011; accepted 17 June 2011 Available online 21 July 2011 Communicated by: Associate Editor Takhir Razykov Abstract An attempt has been made for the determination of diode parameters viz. shunt resistance R sh , series resistance R s , diode ideality factor n and reverse saturation current density J 0 of three solar modules: a-Si 47-37, a-Si 51-13 and CdTe 14407. In this regard, two approaches namely (A) and (B) reported by Khan et al. (2010) have been used to determine all the four diode parameters R sh , R s , n and J 0 . The data of slopes of J–V curve at open circuit conditions (m oc ) and open circuit voltage (V oc ) at different illumination intensities obtained by Del Cueto (1998) for two a-Si and one CdTe solar modules have been used to determine the above diode parameters. The determined values of diode parameters have been used to generate the theoretical J–V curves. The theoretical fill factor (FF) and V oc have been calculated from the theoretical J–V curves and are plotted along with the experimental FF and V oc values. The theoretical values of FF and V oc obtained by the approach (B) of method of Khan et al. (2010) are in good agreement with the experimental values. Ó 2011 Elsevier Ltd. All rights reserved. Keywords: a-Si solar modules; CdTe solar modules; Series resistance; Shunt resistance; Diode ideality factor; Reverse saturation current density 1. Introduction The steady state current density–voltage J–V character- istics of a p–n junction solar cell are usually described based on single exponential model as shown below (Khan et al., 2010). J ¼J ph þ J 0 e qðV JRs Þ nkT  1   þ ðV  JR s Þ R sh ð1Þ where J ph is light generated current density, q is electron charge, k is Boltzmann constant and T is the temperature, R sh is the shunt resistance (in X cm 2 ), R s is the series resis- tance (in X cm 2 ), J 0 is the reverse saturation current density (in A/cm 2 ) and n is the diode ideality factor of the cell. However, R sh , R s , n, J 0 are diode parameters of the cell. Series resistance is the sum of contact resistances of front and back surfaces and resistances of the base region, n + diffuse layer on the front and p + layer on the back side of an n + –p–p + solar cell. It drastically reduces the fill factor (FF) of the cell and thus degrades the cell efficiency. The shunt resistance is owing to a conductive path across the p–n junction or the cell edge. A low value of R sh can affect open circuit voltage (V oc ), FF and thereby the efficiency of the cell significantly. It is well known that J 0 has a decisive effect on V oc . A smaller J 0 results into a higher V oc and thereby into a higher efficiency. The value of ideality factor n is indicative of the recombination mechanism. The values of FF decreases as n increases from n =1 to 2. It is therefore, very important to determine the values of R sh , R s , n and J 0 for a solar cell to find out the cause of power losses in the cell. 0038-092X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2011.06.016 ⇑ Corresponding author at: Physics of Energy Harvesting Division, National Physical Laboratory (CSIR), New Delhi 110 012, India. Tel.: +91 11 45608379; fax: +91 11 45609310. E-mail address: firozkphysics@gmail.com (F. Khan). www.elsevier.com/locate/solener Available online at www.sciencedirect.com Solar Energy 85 (2011) 2288–2294