Influences of Metal Electrodes on Stability of Non‐Fullerene Acceptor‐Based Organic Photovoltaics

Abstract

Understanding chemical degradation at the interface between different layers in an organic photovoltaic device (OPV) is crucial to improving the long‐term stability of OPVs. Herein, molecular‐level insights are provided into the impact of different metal top electrodes on the interfacial morphology and stability of photoactive layers in PM6:Y6 bulk‐heterojunction (BHJ) OPVs. OPVs with an aluminum (Al) top electrode exhibit inferior stability compared to silver (Ag) electrode devices upon thermal annealing, whereby thermal stress induces the diffusion of both Al and Ag atoms to the PM6:Y6 BHJ layer. The diffused Al atoms cause surface recombination at the interface between the photoactive layer and an interlayer. Specifically, X‐ray photoelectron spectroscopy suggests the different local chemical environments of PM6 and Y6 moieties in PM6:Y6/Al‐contact devices. These results are corroborated by solid‐state nuclear magnetic resonance and electron paramagnetic resonance spectroscopy measurements, indicating the formation of ionic and organo‐metallic‐like species at the sub‐layers of the PM6:Y6 BHJ morphology, which are estimated to be less than 5 wt% of the PM6:Y6/Al blend. By comparison, the Ag atoms do not adversely affect PM6:Y6 BHJ morphology and the associated device physics. The investigation of reactive electrode‐BHJ interfaces by multiscale characterization techniques and device physics is expected to provide guidance to future interfacial engineering strategies to develop stable and efficient OPVs.

Importance of Short-Range Order in Governing Thin Film Morphology and Electronic Properties of Polymeric Organic Semiconductors

“…In OSCs, the degree of long-range order can be assessed by X-ray scattering and electron microscopy techniques. − The characterization by such long-range probes may leave a significant degree of intermediate-to-short-range order and disorder unexamined. Specifically, magnetic resonance spectroscopy (NMR and EPR) techniques allow site-specific compositions and structures in both the ordered and disordered regions of OSC materials to be identified and distinguished. ,− The short-range interactions at subnanometer to nanometer distances measured by these techniques also facilitate structure elucidation of OSC thin films. To this end, the emerging NMR crystallography approaches make use of the combined ssNMR, X-ray scattering, and modeling techniques, which are likely to be well-suited to characterize single-component OSCs and organic photovoltaic blends. ,− In a bottom-up strategy, it is first important to resolve the local order in single-component OSCs and then extend it to the study of complex OSC blends.…”

Achieving High Fill Factor in Organic Photovoltaic Cells by Tuning Molecular Electrostatic Potential Fluctuation

“…acceptor-donoracceptor structure and halogen atom modification) to optimize the material structure of OPV cells for more effective photon utilization and the suppression of energy losses (E loss ). [14][15][16][17] Progressing from fullerene acceptors to the ITIC series and then the Y6 series acceptors, J SC has surpassed 28 mA cm À 2 , and E loss has been reduced to nearly 0.5 eV. [18][19][20] Meanwhile, the origins of V OC and J SC also have been widely investigated and a well-defined theoretical framework and a wealth of knowledge have been established.…”

“…Previously, the enhancement of PCEs mainly resulted from developing innovative molecular design strategies (e.g. acceptor‐donor‐acceptor structure and halogen atom modification) to optimize the material structure of OPV cells for more effective photon utilization and the suppression of energy losses ( E loss ) [14–17] . Progressing from fullerene acceptors to the ITIC series and then the Y6 series acceptors, J SC has surpassed 28 mA cm −2 , and E loss has been reduced to nearly 0.5 eV [18–20] .…”

Achieving High Fill Factor in Organic Photovoltaic Cells by Tuning Molecular Electrostatic Potential Fluctuation

“…Previously, the enhancement of PCEs mainly resulted from developing innovative molecular design strategies (e.g. acceptor‐donor‐acceptor structure and halogen atom modification) to optimize the material structure of OPV cells for more effective photon utilization and the suppression of energy losses ( E loss ) [14–17] . Progressing from fullerene acceptors to the ITIC series and then the Y6 series acceptors, J SC has surpassed 28 mA cm −2 , and E loss has been reduced to nearly 0.5 eV [18–20] .…”