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Femtosecond laser excitation (800 nm, ∼150 fs, 80 MHz) induced anisotropic nonlinear optical behaviour and optical limiting action of ethylenediamminium picrate (EDAPA) crystal along two prominent orientations (2 0 0) and (1 1 1) was studied using the Z‐scan technique. EDAPA exhibited reverse saturable type nonlinear absorption ascribed to two‐photon absorption (2PA) process and self‐defocusing based on nonlinear refraction. Intensity dependent nonlinear absorption studies portray the 2PA coefficient is independent of the peak intensity of excitation. Frontier molecular orbitals studies revealed the non‐availability of real states at laser excitation (1.55 eV) and the measured energy gap of 3.18 eV avails the energy states for simultaneous absorption of two photons involving virtual states leading to the occurrence of genuine 2PA. In addition, using molecular electrostatic potential (MEP) analyses polarizability (5.30×10−24 esu) and dipole moment (7.317 Debye) were calculated using the density functional theory. A variation in the NLO coefficients with respect to orientation of excitation arises due to the anisotropy of the crystal. EDAPA crystal along (1 1 1) orientation has high laser damage threshold (9.1 GW/cm2) and low optical limiting threshold (24.36 μJ/cm2) and thus the wide dynamic range make it a preferred candidate towards laser safety devices for high repetition rate ultrashort laser pulse excitation.

Summary Thin film of copper niobate ternary oxide with various compositions was fabricated by pulsed laser deposition technique. Formation of a single phase of monoclinic CuNbO3, monoclinic CuNb3O8 (Cu[I]), and triclinic Cu3Nb2O8 (Cu[II]) thin films was confirmed from the X‐ray diffraction and selected area energy diffraction analysis. Field emission scanning electron microscopy and high‐resolution tunneling electron microscope show CuNbO3 and CuNb3O8 system that exhibits polyhedron and triangular structure, respectively, while Cu3Nb2O8 system shows layered structure formation. The linear spectrum shows a minimal variation in bandgap concerning to the change in elemental composition and position of the copper and niobium atom. Cyclic voltammetry studies endorse that the prepared films are highly adhesive even after 100 cycles. With various compositions of copper niobate thin films as photocathode, N719 sensitized p‐dye‐sensitized solar cells (p‐DSSCs) were fabricated for the first time. Monoclinic CuNbO3 system offers outstanding photovoltaic performance of 2.19% and thus can be used as an alternative for well‐known NiO p‐DSSC. Advantages of copper‐niobium‐oxygen systems open a new route of photocathodic materials for p‐DSSC and tandem solar cells.