Thinning ferroelectric films for high-efficiency photovoltaics based on the Schottky barrier effect

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(Zr 0.2 Ti 0.8)O 3 (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.

Highly Controllable and Silicon-Compatible Ferroelectric Photovoltaic Synapses for Neuromorphic Computing

“…Ferroelectric photovoltaic (FePV) effect offers a viable way of readout, i.e., polarizationcontrolled switchable photocurrent (Yuan et al, 2014;Fan et al, 2015;Ji et al, 2010;Yi et al, 2011;Guo et al, 2013). Using the photocurrent as the readout, ferroelectric materials (in any form and with a broad range of thicknesses) (Tan et al, 2018Yang et al, 2010;Qin et al, 2009;Chen et al, 2011;Bai et al, 2018;He et al, 2019;Blouzon et al, 2016;Alexe and Hesse, 2011) sandwiched between two metal electrodes can in principle function as FePV synapses. Therefore, the limitations in FTJs (ultra-small film thickness and epitaxial growth) and FeFETs (semiconductor channel and optimization of interface quality) no longer exist in the FePV synapses.…”

“…Taking our FePV synapse as an example, it consists of a simple two-terminal Pt/PZT (polycrystalline film)/LNO structure, which can be easily grown on a silicon substrate, demonstrating its good compatibility with the silicon technology. More generally, ferroelectric materials in any form (thin films, Tan et al, 2018;Yang et al, 2010;Qin et al, 2009;Chen et al, 2011;ceramics, Bai et al, 2018;He et al, 2019;single crystals, Blouzon et al, 2016;Alexe et al, 2011;etc.) can be used for constructing FePV synapses because of the universality of the FePV effect. By contrast, FTJs and FeFETs typically require the epitaxy growth (Chen et al, 2018; and careful optimization of the ferroelectric/semiconductor interface quality (Hoffman et al, 2010), respectively, and some of them are difficult to be integrated with the silicon substrate.…”

A Single‐Material Multi‐Source Energy Harvester, Multifunctional Sensor, and Integrated Harvester–Sensor System—Demonstration of Concept

“…[36] Equivalent circuits of piezoelectric, ferroelectric photovoltaic, and pyroelectric energy converters have been reported in literature. [66][67][68] For multi-source energy harvesters which combine different individual piezoelectric, photovoltaic, and pyroelectric components into one circuit platform, the equivalent circuit can be a simple parallel connection of the different components. However, the situation in this work was significantly different as the multiple output source came from a single material instead of three.…”

“…The Schottky diode (D) came with i photo for ferroelectric oxide solar cells. [68] C p and R p are the capacitance and parallel resistance of the KNBNNO, which may be affected by illumination and temperature. [37,62] The series resistance (R s ) accounts for all the voltage drops from the current sources (i photo and i pyro ) to the connection with the external resistive load (R load ).…”

“…[37,62] The series resistance (R s ) accounts for all the voltage drops from the current sources (i photo and i pyro ) to the connection with the external resistive load (R load ). [68,69] Similarly, potential applications can be simultaneous double-source harvesting and sensing of solar (visible light) and thermal (temperature fluctuation) energy sources/stimuli, and harvesting using the photovoltaic effect for DC signals and sensing using the pyroelectric effect with distinguished AC signals (or vice versa). Counterpart concepts have also been reported, including 1) the use of simultaneous coupling of thermoelectric and photoelectric effects in a SnSe:Br semiconductor to convert temperature gradient into electricity via the thermoelectric effect while detecting photons via the photoelectric effect, [70] and 2) the use of carbon sponge material for simultaneous solar distillation and waste heat harvesting (to generate electricity).…”