Abstract
In this work, we apply electric field induced second harmonic generation microscopy to directly observe and quantify space charge accumulation in operating organic bulk heterojunction photovoltaic cells comprised of poly(4,4-dioctyldithieno(3,2-b:2′,3′-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT) mixed with phenyl-C61-butyric acid methyl ester (PCBM). We adjust the effective electron and hole mobility within these blends by altering the relative composition of PSBTBT and PCBM, and observe dramatic shifts in space charge accumulation. The PSBTBT rich device shows strong electron accumulation (2.8×1014e−/cm3) and the PCBM rich device shows strong hole accumulation (5.5×1014h+/cm3).
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