Peptides have attracted considerable attention due to their biocompatibility, functional molecular recognition and unique biological and electronic properties. The strong piezoelectricity in diphenylalanine peptide expands its technological potential as a smart material. However, its random and unswitchable polarization has been the roadblock to fulfilling its potential and hence the demonstration of a piezoelectric device remains lacking. Here we show the control of polarization with an electric field applied during the peptide self-assembly process. Uniform polarization is obtained in two opposite directions with an effective piezoelectric constant d33 reaching 17.9 pm V−1. We demonstrate the power generation with a peptide-based power generator that produces an open-circuit voltage of 1.4 V and a power density of 3.3 nW cm−2. Devices enabled by peptides with controlled piezoelectricity provide a renewable and biocompatible energy source for biomedical applications and open up a portal to the next generation of multi-functional electronics compatible with human tissue.

The desire for self-powered nanosystems and wearable devices has driven wide investigation of the sustainable energy source. Harvesting energy from the ambient environment with nanogenerators becomes a viable solution with the development of low-power electronics. Different devices can face dramatically different working conditions, which may seriously restrict the application of those nanogenerators. In this review article we describe the most recent progress in the study of the environmental effect on the nanogenerator. While a variety of nanogenerators have been developed using piezoelectric, triboelectric, pyroelectric and thermoelectric effects, the most studied piezoelectric nanogenerator and triboelectric nanogenerator will be discussed in more detail. This review emphasizes the important effect of the temperature, humidity, and water. The other effects, such as UV radiation or adsorption of gas or solid material, are also presented for certain nanogenerators. In the end we share our views of the future research directions and the remaining challenges in this field.

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Strain-induced polarization charges in a piezoelectric semiconductor effectively modulate the band structure near the interface and charge carrier transport. Fundamental investigation of the piezotronic effect has attracted broad interest, and various sensing applications have been demonstrated. This brief review discusses the fundamentals of the piezotronic effect, followed by a review highlighting important applications for strain sensors, pressure sensors, chemical sensors, photodetectors, humidity sensors and temperature sensors. Finally, the review offers some perspectives and outlook for this new field of multi-functional sensing enabled by the piezotronic effect.

The strain-induced band structure change in a semiconductor can change its resistivity, known as the piezoresistive effect. If the semiconductor is also a piezoelectric material, strain-induced polarization charge can control the current transport at the metal-semiconductor contact, which is called a 'piezotronic effect'. Piezotronic effect is intertwined with piezoresistive effect in the study of present piezotronic nanowire devices. Decoupling those effects will facilitate the fundamental study on the piezotronic devices and simplify the data analysis in real applications. Here, we report a general method to separate the piezotronic and piezoresistive effects in the same nanowire, based on modified four-point measurements. Current transport characteristics of each contact was extracted and showed different responses to the strain. The piezoresistive effect was measured in zinc oxide nanowires for the first time, and the result confirmed the dominant role of piezotronic effect in the strain-induced change of transport characteristics in a piezoelectric semiconductor. This study validates the assumption made in present piezotronic devices and provides a guideline for further investigation.