The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in amorphous silicon and its compounds are the object of intense research works. By starting on the concept that such p-i-n structures can be compared to p(+)-n and n-n(+) junctions in series, and by referring to Shockley's model in one modified diode, we propose an equivalent electrical circuit in dynamic state of the considered structure resulting from a series association of Shockley's model. A simulation study by PSPICE of the equivalent electrical circuit so obtained is in good agreement with the experimental results, and physical interpretations connected to this model are discussed. (c) 2007 Elsevier Ltd. All rights reserved.