Improved ferroelectric photovoltaic effect in Mn-doped lead-free K0.5Na0.5NbO3 films

The pure and Mn-doped K0.5Na0.5NbO3 (KNN) films were deposited using solution-gelation method. The crystal structure, ferroelectric properties, spectral response and J-V performance of photovoltaic effect were systematically investigated. Both the ferroelectric and leakage properties are obviously enhanced for Mn-doped KNN films. A fascinating phenomenon is observed that the ferroelectric photovoltaic effect is enhanced in Mn-doped KNN films, which is originated from the improved ferroelectric polarization and narrower band gap. The transition element Nb partially substituted by Mn results in the lattice distortion and further destroys the symmetry space structure, which enhances ferroelectric polarization. And the narrower band gap effectively decreases the internal potential barrier to separate the carriers. This work gives a clear relationship between the lattice distortion, ferroelectric and photovoltaic response. It is certain that lead-free transparent K0.5Na0.5NbO3 films can be potentially applied in viable ferroelectric based solar cells.