TY - JOUR
T1 - Charge and Triplet Exciton Generation in Neat PC70\nBM Films and Hybrid CuSCN:PC70\nBM Solar Cells
AU - Karuthedath, Safakath
AU - Gorenflot, Julien
AU - Firdaus, Yuliar
AU - Sit, Wai-Yu
AU - Eisner, Flurin
AU - Seitkhan, Akmaral
AU - Ravva, Mahesh Kumar
AU - Anthopoulos, Thomas D.
AU - Laquai, Frédéric
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: S.K. and J.G. contributed equally to this work. The research reported in this publication was supported by funding from the King Abdullah University of Science and Technology (KAUST).
PY - 2018/11/8
Y1 - 2018/11/8
N2 - Organic solar cells that use only fullerenes as the photoactive material exhibit poor exciton-to-charge conversion efficiencies, resulting in low internal quantum efficiencies (IQE). However, the IQE can be greatly improved, when copper(I) thiocyanate (CuSCN) is used as a carrier-selective interlayer between the phenyl-C70-butyric acid methyl ester (PC70BM) layer and the anode. Efficiencies of ≈5.4% have recently been reported for optimized CuSCN:PC70BM (1:3)-mesostructured heterojunctions, yet the reasons causing the efficiency boost remain unclear. Here, transient absorption (TA) spectroscopy is used to demonstrate that CuSCN does not only act as a carrier-selective electrode layer, but also facilitates fullerene exciton dissociation and hole transfer at the interface with PC70BM. While intrinsic charge generation in neat PC70BM films proceeds with low yield, hybrid films exhibit much improved exciton dissociation due to the presence of abundant interfaces. Triplet generation with a rate proportional to the product of singlet and charge concentrations is observed in neat PC70BM films, implying a charge–singlet spin exchange mechanism, while in hybrid films, this mechanism is absent and triplet formation is a consequence of nongeminate recombination of free charges. At low carrier concentrations, the fraction of charges outweighs the population of triplets, leading to respectable device efficiencies under one sun illumination.
AB - Organic solar cells that use only fullerenes as the photoactive material exhibit poor exciton-to-charge conversion efficiencies, resulting in low internal quantum efficiencies (IQE). However, the IQE can be greatly improved, when copper(I) thiocyanate (CuSCN) is used as a carrier-selective interlayer between the phenyl-C70-butyric acid methyl ester (PC70BM) layer and the anode. Efficiencies of ≈5.4% have recently been reported for optimized CuSCN:PC70BM (1:3)-mesostructured heterojunctions, yet the reasons causing the efficiency boost remain unclear. Here, transient absorption (TA) spectroscopy is used to demonstrate that CuSCN does not only act as a carrier-selective electrode layer, but also facilitates fullerene exciton dissociation and hole transfer at the interface with PC70BM. While intrinsic charge generation in neat PC70BM films proceeds with low yield, hybrid films exhibit much improved exciton dissociation due to the presence of abundant interfaces. Triplet generation with a rate proportional to the product of singlet and charge concentrations is observed in neat PC70BM films, implying a charge–singlet spin exchange mechanism, while in hybrid films, this mechanism is absent and triplet formation is a consequence of nongeminate recombination of free charges. At low carrier concentrations, the fraction of charges outweighs the population of triplets, leading to respectable device efficiencies under one sun illumination.
UR - http://hdl.handle.net/10754/629866
UR - https://onlinelibrary.wiley.com/doi/full/10.1002/aenm.201802476
UR - http://www.scopus.com/inward/record.url?scp=85056194103&partnerID=8YFLogxK
U2 - 10.1002/aenm.201802476
DO - 10.1002/aenm.201802476
M3 - Article
SN - 1614-6832
VL - 9
SP - 1802476
JO - Advanced Energy Materials
JF - Advanced Energy Materials
IS - 1
ER -