ИСТИНА

In recent years, the efficiency of organic solar cells (OSC) grows very fast, however it is still lower than for traditional inorganic solar cells. It is well known that inorganic solar cells are based on doped semiconductors, for OSC it only recently has been shown that doping can increase efficiency. The form of current-voltage characteristics is of great importance for high-efficient OSC. In this paper we show that doping can strongly influence the fill factor of bilayer organic solar cells with planar heterojunction. We use drift-diffusion numerical model of bilayer OSC with fielddependent charge dissociation at the donor-acceptor interface. The input parameters are taken corresponding to the most studied polymer-fullerene OSCs. The results of modeling show, that at minority carrier doping, i.e. when the electronconducting acceptor layer is p-doped and the hole-conducting donor layer is n-doped the fill factor dramatically drops relatively to undoped cell, so the current voltage curve becomes S-shaped. In contrary, at majority carrier doping, i.e. when donor layer is p-doped and acceptor layer is n-doped, the fill factor increases and can exceed Shockley-Queisser limit for fill factor of inorganic p-n junction solar cells. Such Shockley-Queisser limit exceeding is due to field dependence of electron-hole pair separation at donor acceptor interface, which leads to steeper current-voltage characteristics. Open-circuit also increases with majority-carrier dopant concentration and can become higher than built-in voltage. This work was supported by Russian Foundation for Basic Research (grant 14-02-31823 mol_a).