Lending Triarylphosphine Oxide to Phenanthroline: a Facile Approach to High‐Performance Organic Small‐Molecule Cathode Interfacial Material for Organic Photovoltaics utilizing Air‐Stable Cathodes

Abstract

Cathode interfacial material (CIM) is critical to improving the power conversion efficiency (PCE) and long‐term stability of an organic photovoltaic cell that utilizes a high work function cathode. In this contribution, a novel CIM is reported through an effective and yet simple combination of triarylphosphine oxide with a 1,10‐phenanthrolinyl unit. The resulting CIM possesses easy synthesis and purification, a high T g of 116 °C and attractive electron‐transport properties. The characterization of photovoltaic devices involving Ag or Al cathodes shows that this thermally deposited interlayer can considerably improve the PCE, due largely to a simultaneous increase in V oc and FF relative to the reference devices without a CIM. Notably, a PCE of 7.51% is obtained for the CIM/Ag device utilizing the active layer PTB7:PC71BM, which far exceeds that of the reference Ag device and compares well to that of the Ca/Al device. The PCE is further increased to 8.56% for the CIM/Al device (with J sc = 16.81 mA cm−2, V oc = 0.75 V, FF = 0.68). Ultraviolet photoemission spectroscopy studies reveal that this promising CIM can significantly lower the work function of the Ag metal as well as ITO and HOPG, and facilitate electron extraction in OPV devices.

Roll to roll compatible fabrication of inverted organic solar cells with a self-organized charge selective cathode interfacial layer

“…Previous reports suggested that Phen-NaDPO may even participate in the charge transfer process from PCBM to the electrode, a hypothesis which minimizes the energy loss during electron extraction. 30 Finally, we found that self-organization from "ternary" composites works well for bare ITO and ITO/AZO substrates (see ESI Fig. S3 and S4 †).…”

“…Phen-NaDPO was already shown to be a versatile cathode modication layer for Ag, ITO and HOPG due to its strong interaction with the substrates. 30 We studied this effect for various metal oxide substrates using Kelvin probe spectroscopy (see ESI Table S2 †). As expected, coating a thin layer of PhenNaDPO decreases the work functions for ITO, ITO/AZO and ITO/ ZnO to 4.01, 3.92 and 3.83 eV, respectively.…”

“…30,31 Furthermore, it should be emphasized, different from the strongly hydrophilic CIMs such as PEI, Phen-NaDPO exhibits good solubility in weakly polar solvents, such as chlorobenzene (CB) and o-dichlorobenzene (ODCB). Consequently, no additional polar solvent is needed in processing the active layer, thus facilitating the large-scale roll-to-roll production with high reproducibility and reliability.…”

Interfacial Layer Engineering for Performance Enhancement in Polymer Solar Cells

“…The work function decreasing ability of Phen-NaDPO is further investigated on both ITO and inert graphite substrate. The result shows that the work function of substrates can be reduced to 3.02 and 3.10 eV for graphite and ITO, respectively, which suggests the Phen-NaDPO potential of being a universal material to reduce work function for different substrates [79].…”

Molecular engineering and sequential cosensitization for preventing the “trade-off” effect with photovoltaic enhancement

“…6 Generally, broad absorption spectra can be obtained through decreasing the band gap between the HOMO and LUMO orbitals of the photosensitizers. 7 Meanwhile, a potential offset is required to act as the driving force for electron injection from the excited dyes to the TiO 2 conduction band (0.5 V vs. NHE) and dye regeneration by accepting electrons from an iodine electrolyte (0.4 V vs. NHE).…”