I have read a journal in theoretical modeling of organic solar cells. But I couldn't understand how it is used in this particular problem and how it calculates physical quantities. Could someone help me?
If you are, however, looking for a more analytic way to perform these calculations yourself, I recommend starting from the tutorial review of Myroshnychenko et al. [Chem.Soc.Rev., 2008, 37 , 1792–1805]. Here you learn step by step how to calculate absorption for single particles and for particle arrays using effective medium theory. Also it gives a comparison of different exact numerical approaches (BEM, DDA, FDTD and others) providing all necessary equations.