Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells with High Open-Circuit Voltage
Artikel i vetenskaplig tidskrift, 2012

In organic solar cells based on polymer:fullerene blends, energy is lost due to electron transfer from polymer to fullerene. Minimizing the difference between the energy of the polymer exciton (ED*) and the energy of the charge transfer state (ECT) will optimize the open-circuit voltage (Voc). In this work, this energy loss ED*-ECT is measured directly via Fourier-transform photocurrent spectroscopy and electroluminescence measurements. Polymer:fullerene photovoltaic devices comprising two different isoindigo containing polymers: P3TI and PTI-1, are studied. Even though the chemical structures and the optical gaps of P3TI and PTI-1 are similar (1.4 eV1.5 eV), the optimized photovoltaic devices show large differences in Voc and internal quantum efficiency (IQE). For P3TI:PC71BM blends a ED*-ECT of similar to 0.1 eV, a Voc of 0.7 V and an IQE of 87% are found. For PTI-1:PC61BM blends an absence of sub-gap charge transfer absorption and emission bands is found, indicating almost no energy loss in the electron transfer step. Hence a higher Voc of 0.92 V, but low IQE of 45% is obtained. Morphological studies and field dependent photoluminescence quenching indicate that the lower IQE for the PTI-1 system is not due to a too coarse morphology, but is related to interfacial energetics. Losses between ECT and qVoc due to radiative and non-radiative recombination are quantified for both material systems, indicating that for the PTI-1:PC61BM material system, Voc can only be increased by decreasing the non-radiative recombination pathways. This work demonstrates the possibility of obtaining modestly high IQE values for material systems with a small energy offset (<0.1 eV) and a high Voc.

charge transfer state

organic solar cell

fullerene

conjugated polymer

Författare

K. Vandewal

Linköpings universitet

Z. F. Ma

Linköpings universitet

J. Bergqvist

Linköpings universitet

Z. Tang

Linköpings universitet

Ergang Wang

Chalmers, Kemi- och bioteknik, Polymerteknologi

Patrik Henriksson

Chalmers, Kemi- och bioteknik, Polymerteknologi

K. Tvingstedt

Linköpings universitet

Mats Andersson

Chalmers, Kemi- och bioteknik, Polymerteknologi

Fengling Zhang

Linköpings universitet

Olle Inganäs

Linköpings universitet

Advanced Functional Materials

1616-301X (ISSN)

Vol. 22 16 3480-3490

Ämneskategorier

Kemi

DOI

10.1002/adfm.201200608

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2021-07-08