TY - JOUR
T1 - Photoinduced Charge Carrier Generation and Decay in Sequentially Deposited Polymer/Fullerene Layers: Bulk Heterojunction vs. Planar Interface
AU - Nardes, Alexandre M.
AU - Ayzner, Alexander L.
AU - Hammond, Scott R.
AU - Ferguson, Andrew J.
AU - Schwartz, Benjamin J.
AU - Kopidakis, Nikos
PY - 2012/4/5
Y1 - 2012/4/5
N2 - In this work, we use the time-resolved microwave conductivity (TRMC) technique to study the dynamics of charge carrier generation in sequentially deposited conjugated polymer/fullerene layers. These layers are either fully solution-processed, using orthogonal solvents for the layers of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene phenyl-C 61-butyric acid methyl ester (PCBM), or prepared by thermally evaporating a C 60 layer onto P3HT films. Our work is motivated by the remarkable efficiency of organic photovoltaic (OPV) devices using a sequentially processed P3HT/PCBM active layer. Here we use an electrodeless photoconductivity probe, so we can photoexcite the sample either through the polymer or the fullerene layer. We use samples with extremely thick P3HT films (2.4 μm) and show that excitation from either side of both as-cast and thermally annealed sample yields virtually identical results, consistent with mixing of the PCBM into the polymer film. We also compare solution-deposited samples to samples made by thermally evaporating C 60 on P3HT, and find that we can distinguish between charge generation in bulk-P3HT and at the polymer/fullerene interface. We show that, despite their morphological differences, the carrier dynamics in the sequentially processed samples resemble those of mixed, bulk heterojunction (BHJ) systems. All of this is consistent with the idea that PCBM readily mixes into the P3HT film in sequentially deposited P3HT/PCBM samples, although the total amount of fullerene mixed into the P3HT appears to be less than that typically used in an optimized BHJ. Finally, we discuss the implications for OPV device architectures prepared by sequential deposition from solution.
AB - In this work, we use the time-resolved microwave conductivity (TRMC) technique to study the dynamics of charge carrier generation in sequentially deposited conjugated polymer/fullerene layers. These layers are either fully solution-processed, using orthogonal solvents for the layers of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene phenyl-C 61-butyric acid methyl ester (PCBM), or prepared by thermally evaporating a C 60 layer onto P3HT films. Our work is motivated by the remarkable efficiency of organic photovoltaic (OPV) devices using a sequentially processed P3HT/PCBM active layer. Here we use an electrodeless photoconductivity probe, so we can photoexcite the sample either through the polymer or the fullerene layer. We use samples with extremely thick P3HT films (2.4 μm) and show that excitation from either side of both as-cast and thermally annealed sample yields virtually identical results, consistent with mixing of the PCBM into the polymer film. We also compare solution-deposited samples to samples made by thermally evaporating C 60 on P3HT, and find that we can distinguish between charge generation in bulk-P3HT and at the polymer/fullerene interface. We show that, despite their morphological differences, the carrier dynamics in the sequentially processed samples resemble those of mixed, bulk heterojunction (BHJ) systems. All of this is consistent with the idea that PCBM readily mixes into the P3HT film in sequentially deposited P3HT/PCBM samples, although the total amount of fullerene mixed into the P3HT appears to be less than that typically used in an optimized BHJ. Finally, we discuss the implications for OPV device architectures prepared by sequential deposition from solution.
KW - fullerene layer
KW - polymer film
KW - time-resolved microwave conductivity
KW - TRMC
UR - http://www.scopus.com/inward/record.url?scp=84859575070&partnerID=8YFLogxK
U2 - 10.1021/jp212390p
DO - 10.1021/jp212390p
M3 - Article
AN - SCOPUS:84859575070
SN - 1932-7447
VL - 116
SP - 7293
EP - 7305
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 13
ER -