Band unpinning and photovoltaic model for P3HT:PCBM organic bulk heterojunctions under illumination

Linear plots of C −2 vs. voltage in P3HT-PCBM organic solar cells, shitf under illumination, indicating the charging of a surface state. Capacitance analysis of P3HT:PCBM bulk heterojunction solar cells, in dark and under illumination, shows a linear Mott–Schottky characteristic at moderate reverse...

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Bibliographic Details
Published in:Chemical physics letters 2008-11, Vol.465 (1), p.57-62
Main Authors: Bisquert, Juan, Garcia-Belmonte, Germà, Munar, Antoni, Sessolo, Michele, Soriano, Alejandra, Bolink, Henk J.
Format: Article
Language:English
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Summary:Linear plots of C −2 vs. voltage in P3HT-PCBM organic solar cells, shitf under illumination, indicating the charging of a surface state. Capacitance analysis of P3HT:PCBM bulk heterojunction solar cells, in dark and under illumination, shows a linear Mott–Schottky characteristic at moderate reverse bias, indicating p-doping of the organic blend. The flatband potential under illumination is displaced negatively about 0.6 V with respect to dark conditions. A basic photovoltaic model is developed to explain this, in terms of electron transfer via surface states at the metal/organic interface. Surface states with a slow exchange kinetics, become charged under illumination, unpinning the band and decreasing the depletion layer at the electron extraction contact. This becomes a major factor limiting the performance of bulk heterojunction solar cells.
ISSN:0009-2614
1873-4448
DOI:10.1016/j.cplett.2008.09.035