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Photoconversion in organic photovoltaic cells (OPVs) is limited by carrier recombination that frustrates charge collection at the electrodes. Consequently, identification of the dominant recombination mechanisms is critical to inform device design for improved performance. This analysis is complicated by the need to have a quantitative measure of carrier generation. Here, we demonstrate a photovoltage-based technique to directly investigate the generation of charge carriers in OPVs. This technique allows illuminated current losses to both geminate and non-geminate recombination to be directly quantified as a function of voltage. While broadly applicable, here the technique is demonstrated on OPVs based on the donor–acceptor pairings of 2-((7-(4- N , N -ditolylaminophenylen-1-yl)benzo[ c ][1,2,5]thiadiazol-4-yl)methylene)malononitrile (DTDCPB)-C 60 and copper phthalocyanine (CuPc)-C 60 . Both structures are limited by geminate recombination at short-circuit and under reverse bias. Under forward bias, the severity of non-geminate recombination depends on both materials selection and device architecture. Consequently, this technique quantitatively casts changes in performance with choice of OPV architecture in terms of the relative roles of geminate and non-geminate recombination.
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Decoupling Photocurrent Loss Mechanisms in Photovoltaic Cells Using Complementary Measurements of Exciton Diffusion
Abstract Significant work has been directed at measuring the exciton diffusion length (LD) in organic semiconductors due to its significance in determining the performance of photovoltaic cells. Several techniques have been developed to measureLD, often probing photoluminescence or charge carrier generation. Interestingly, in this study it is shown that when different techniques are compared, both the diffusive behavior of the exciton and active carrier recombination loss pathways can be decoupled. Here, a planar heterojunction device based on the donor–acceptor pairing of boron subphthalocyanine chloride‐C60is examined using photoluminescence quenching, photovoltage‐, and photocurrent‐basedLDmeasurement techniques. Photovoltage yields the device relevantLDof both active materials as a function of forward bias subject to geminate recombination losses. These values are used to accurately predict the photocurrent as a function of voltage, suggesting geminate recombination is the dominant mechanism responsible for photocurrent loss. By combining these measurements with photocurrent and photoluminescence quenching, the intrinsicLD, as well as the voltage‐dependent charge transfer state dissociation and charge collection efficiencies are quantitatively determined. The results of this work provide a method to decouple all relevant loss pathways during photoconversion, and establish the factors that can limit the performance of excitonic photovoltaic cells.
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- Award ID(s):
- 1708177
- PAR ID:
- 10049976
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 8
- Issue:
- 13
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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