Abstract
Achieving high power conversion efficiencies (PCEs) in ferroelectric photovoltaics (PVs) is a longstanding challenge. Although recently ferroelectric thick films, composite films, and bulk crystals have all been demonstrated to exhibit PCEs >1%, these systems still suffer from severe recombination because of the fundamentally low conductivities of ferroelectrics. Further improvement of PCEs may therefore rely on thickness reduction if the reduced recombination could overcompensate for the loss in light absorption. Here, a PCE of up to 2.49% (under 365-nm ultraviolet illumination) was demonstrated in a 12-nm Pb(Zr0.2Ti0.8)O3 (PZT) ultrathin film. The strategy to realize such a high PCE consists of reducing the film thickness to be comparable with the depletion width, which can simultaneously suppress recombination and lower the series resistance. The basis of our strategy lies in the fact that the PV effect originates from the interfacial Schottky barriers, which is revealed by measuring and modeling the thickness-dependent PV characteristics. In addition, the Schottky barrier parameters (particularly the depletion width) are evaluated by investigating the thickness-dependent ferroelectric, dielectric and conduction properties. Our study therefore provides an effective strategy to obtain high-efficiency ferroelectric PVs and demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices.
Highlights
The ferroelectric photovoltaic (PV) effect has gained widespread attention in the past decade[1,2,3,4,5] because of its promising applications in solar energy harvesting[6,7,8], selfpowered photodetection[9,10], and information storage[11,12]
The peaks in the range of 42.35° to 42.63° correspond to larger lattice constants: c2 = 4.232–4.259 Å. These results suggest that our PZT films may contain two tetragonal phases: a bulk-like T1 phase that exists near the top of the film and is almost strainfree and a strained T2 phase that exists near the bottom of the film and undergoes lattice relaxation as the film becomes thicker
Our strategy to realize such a high power conversion efficiencies (PCEs) consists of reducing the film thickness to be close to the depletion width, which can simultaneously suppress recombination and lower the series resistance
Summary
The ferroelectric photovoltaic (PV) effect has gained widespread attention in the past decade[1,2,3,4,5] because of its promising applications in solar energy harvesting[6,7,8], selfpowered photodetection[9,10], and information storage[11,12]. The high PCEs (>1%) of ferroelectric PVs were achieved mostly in thick films[6,18], composite films[19,20,21], and bulk crystals[17], all of which have large thicknesses (several hundred nanometers and above). In these systems, severe recombination may occur because ferroelectrics have fundamentally low carrier mobilities and short lifetimes.
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