Tham khảo tài liệu 'solar energy 2012 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Organic Solar Cells Performances Improvement Induced by Interface Buffer Layers 233 interface dipole ID resulting from charge rearrangement upon interface formation Lee et al. Appl. Phys. Lett. 2009 . In the case of inorganic metal semiconductor contacts two limit models have been proposed. The Schottky-Mott model where the vacuum level of the organic and metal aligned forming a region of net space charge at the interface and the Bardeen model where a large density of surface states induces a pining effect of the Fermi level and the presence at the interface of a barrier independent of the metal work function. The Cowley-Sze model is an intermediate model where interface states would be induced in the original band gap of the semiconductor upon contact with a metal giving the interfacial dipole A . The effective barrier height for hole exchange ob f- is therefore given by B eff Ob - A 4 A is proportional to the amount of charge transferred due to energy difference between the metal Fermi level and the charge neutrality level CNL . If we assume a uniform distribution of metal-induced interface state it can be shown that OB eff varies linearly with the metal work function with a slope S smaller than one Lee et al. Appl. Phys. Lett . 2009 . In the absence of metal-induced interface state the injection barrier follows the Schottky-Mott limit with S 1. The other limit corresponds to S 0 the interface dipole reaches a saturated value with the organic CNL aligned to the metal s Fermi level. There is Fermi level pining and the variation of the metal work function is fully compensated by the metal-induced interface state dipole. By analogy with inorganic metal semiconductor contacts two limit models have been proposed when an organic semiconductor is deposited onto a conducting material. The first is the above described Schottky-Mott simple model. The second proposed that a charge dipole forms on the interface due to effect such as chemical interaction and or formation of .
