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Influence of Phonon Scattering on Exciton and Charge Diffusion in Polymer‐Fullerene Solar Cells
Author(s) -
Presselt Martin,
Herrmann Felix,
Hoppe Harald,
Shokhovets Sviatoslav,
Runge Erich,
Gobsch Gerhard
Publication year - 2012
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201100793
Subject(s) - materials science , exciton , polymer solar cell , charge carrier , scattering , organic solar cell , fullerene , phonon scattering , crystallinity , phonon , heterojunction , optoelectronics , solar cell , chemical physics , condensed matter physics , polymer , chemistry , physics , optics , organic chemistry , composite material , thermal conductivity
Thermally activated transport and phonon scattering in P3HT:PCBM (poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenylC61‐butyric acid methyl ester) bulk heterojunction (BHJ) organic solar cells is studied via temperature‐dependent external‐quantum‐efficiency (EQE) spectroscopy. The hopping barriers for combined exciton and charge transport are balanced for the individual blended materials in a sample, which possesses a blending ratio and a morphology that give rise to a maximal power‐conversion efficiency. Increasing the PCBM weight fraction leads to a reduction of exciton hopping barriers in PCBM, while for P3HT exciton hopping barriers remain constant. This reduction of PCBM exciton hopping barriers is attributed to a higher PCBM crystallinity in the PCBM‐rich solar cell as compared to the BHJ with the optimized blending ratio. The morphology‐dependent difference in exciton hopping activation energies between P3HT and PCBM is attributed to a higher impact of phonon scattering in P3HT than in PCBM, as concluded from the much stronger decrease of P3HT‐related temperature‐dependent external quantum efficiencies above room temperature in the PCBM‐rich BHJ solar cell. All EQE data of P3HT:PCBM‐based BHJ solar cells is modeled consistently over a broad temperature range by a simple analytical expression involving temperature activation and phonon scattering, without the need to distinguish two separate hopping regimes.