Abstract
AbstractThe bulk photovoltaic effect (BPVE) refers to the generation of a steady photocurrent and above-bandgap photovoltage in a single-phase homogeneous material lacking inversion symmetry. The mechanism of BPVE is decidedly different from the typical p–n junction-based photovoltaic mechanism in heterogeneous materials. Recently, there has been renewed interest in ferroelectric materials for solar energy conversion, inspired by the discovery of above-bandgap photovoltages in ferroelectrics, the invention of low bandgap ferroelectric materials and the rapidly improving power conversion efficiency of metal halide perovskites. However, as long as the nature of the BPVE and its dependence on composition and structure remain poorly understood, materials engineering and the realisation of its true potential will be hampered. In this review article, we survey the history, development and recent progress in understanding the mechanisms of BPVE, with a focus on the shift current mechanism, an intrinsic BPVE that is universal to all materials lacking inversion symmetry. In addition to explaining the theory of shift current, materials design opportunities and challenges will be discussed for future applications of the BPVE.
Highlights
The photovoltaic (PV) effect, which is the direct conversion of light to electricity, is regarded as one of the most reliable and abundant sources of renewable and clean energy
We discuss the bulk photovoltaic effect (BPVE), in particular, the shift current mechanism, which has a number of advantages over traditional p–n junction-based solar cells
The carriers in p–n junctions travel to the electrodes via drift-diffusive transport, shift current carriers instead rapidly propagate to the electrodes, minimising the opportunity for energy losses
Summary
The photovoltaic (PV) effect, which is the direct conversion of light to electricity, is regarded as one of the most reliable and abundant sources of renewable and clean energy. We discuss the bulk photovoltaic effect (BPVE), in particular, the shift current mechanism, which has a number of advantages over traditional p–n junction-based solar cells. The carriers in p–n junctions travel to the electrodes via drift-diffusive transport, shift current carriers instead rapidly propagate to the electrodes, minimising the opportunity for energy losses Because this is a hot carrier effect, carrier separation does not depend on any internal electric fields (see the ‘Polarisation’ section), above-bandgap photovoltages can be generated, and the Shockley–Queisser limit could be surpassed. The matrix element describing the interference, in equation (4), does not vanish by symmetry In real materials, this asymmetry is manifested in the different spatial character of conduction and valence bands.[31] Heuristically, this causes the electrons (and holes) to ‘shift’ on excitation by light. The response function can be written as an integral over the Brillouin zone.[24]
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