ИСТИНА

Organic semiconductors that constitute the active layer of organic solar cells contain numerous defects and impurities, which can be charged and act as dopants. However, in modeling organic solar cells, the active layer is usually assumed to be undoped. Conventional numerical models account for generation, recombination, drift and diffusion of charge carriers, space charge effects, etc. We have extended these models for planar and bulk heterojunction solar cells by introducing dopants in the active layer and studied their performance upon n- and p-doping. For bulk heterojunction cell with optimized parameters based on the most studied material pair (P3HT and PCBM) we have found that the efficiency decreases from 4.5% to 1% upon doping due to decrease of the short-circuit current and fill factor; the open-circuit voltage changes slightly. However, for non-optimized cells doping can increase efficiency. For example, in cases of low charge carrier mobilities, unbalanced mobilities and non-ohmic contacts the efficiency can be increased by several times upon doping. For bilayer organic solar cells we show that doping of layers by majority carriers (i.e. the donor/acceptor layer is p/n-doped) increases the short-circuit current, open-circuit voltage, fill factor and efficiency. Upon doping a P3HT/PCBM bilayer cell, the efficiency can be increased by more than three times. Reversely, i.e. upon doping by minority carriers, the efficiency decreases and the I/V curve becomes S-shaped.