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p-Type Semiconductor Nickel Oxide as an Anodal Interfacial Layer in Organic Photovoltaics

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Background: Northwestern researchers developed organic photovoltaic (OPV) cells that offer a potential alternative to conventional Si solar cells. Technology Description: The OPVs developed use the typical poly(3-hexylthiophene) (P3HT) and fullerene derivative [66]-phenyl-C61 butyric acid methyl ester (PCBM) active layer but replace the typical electron blocking layer (EBL)/hole-transporting layer (HTL) Poly(34-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with the novel composition nickel oxide. Nickel oxide (NiO) a cubic wide band-gap semiconductor which is essentially transparent as very thin layers is a p-type to facilitate hole conduction (HTL). This novel composition is designed to enhance OPV performance by reducing loss of open-circuit voltage that is common with other cells. NiO has a band structure well-suited for P3HT:PCBM OPVs and provides an ohmic contact to P3HT while having a sufficiently high conduction band minimum to function as an EBL. The device structure of glass/ITO/NiO/P3HT:PCBM/LiF/Al reported here proved an effective PEDOT:PSS replacement affording both exceptional fill factor (69%) and open-circuit voltage (638 mV) metrics as well as a BHJ cell power conversion efficiency of 5.2% versus a glass/ITO/P3HT:PCBM/LiF/Al control device (51% 0.515mv 2.9% respectively). Replacement of PEDOT:PSS with a p-type oxide semiconductor anode interfacial layer in an archetypical BHJ photovoltaic device results in a dramatic performance increase while exhibiting excellent device stability. The value of such hole-transporting/electron-blocking interfacial layers is clearly demonstrated and should be applicable to other organic photovoltaics. Applications: For use in organic photovoltaic devices Patent Status: A patent application has been filed.

Benefits:

1) Reduced interfacial power losses in BHJ photovoltaics 2) Enhanced OPV device stability 3) Eliminate use of PEDOT:PSS in OPVs 4) Low cost 5) Lightweight with mechanical flexibility 6) Suitable to high-throughput low-cost reel-to-reel coating processes

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Patent application filed