Abstract
Harvesting of solar energy by hot carriers from optically induced intraband transitions offers new perspectives for photovoltaic energy conversion. Clearly, mechanisms slowing down hot-carrier thermalization constitute a fundamental core of such pathways of third-generation photovoltaics. The intriguing concept of hot polarons stabilized by long-range phonon correlations in charge-ordered strongly correlated three-dimensional metal-oxide perovskite films has emerged and been demonstrated for ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}\mathrm{O}}_{3}$ at low temperature. In this work, a tailored approach to extending such processes to room temperature is presented. It consists of a specially designed epitaxial growth of two-dimensional Ruddlesden-Popper ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{1.5}{\mathrm{Mn}\mathrm{O}}_{4}$ films on $\mathrm{Nb}$:${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ with a charge-ordering transition at ${T}_{\mathrm{CO}}$ \ensuremath{\sim} 320 K. This opens the route to a different phonon-bottleneck strategy of slowing down carrier relaxation by strong coupling of electrons to cooperative lattice modes.
Highlights
Establishing new mechanisms that overcome the constraints for photovoltaic energy conversion of conventional semiconductors due to transmission and thermalization losses is a high-priority goal of third-generation photovoltaics, for example, highly efficient solar cells that are based on thin films [1,2]
The orthorhombic crystal structure of RuddlesdenPopper manganite Pr0.5Ca1.5MnO4 (RP PCMO) is comprised of a perovskite layer AMnO3 (A = Pr, Ca) separated by a rock-salt-layer AO, yielding a 2D network of MnO6 octahedra
The RP PCMO belongs to the space group Fmm2 with a = 0.5365 nm, b = 0.5354 nm, and c = 1.1840 nm [24]
Summary
Establishing new mechanisms that overcome the constraints for photovoltaic energy conversion of conventional semiconductors due to transmission and thermalization losses is a high-priority goal of third-generation photovoltaics, for example, highly efficient solar cells that are based on thin films [1,2]. A primary goal to achieve higher efficiency is to overcome the Shockley-Queisser limit in semiconductors [3]. It arises from transmission losses of photons with energy below the bandgap as well as thermalization losses of hot carriers excited above the bandgap. The harvesting of hot carriers that normally undergo fast subpicosecond thermalization by scattering on optical phonons would be a major step into that direction.
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