Phosphorus-doped zinc oxide p–n homojunction thin film for flexible piezoelectric nanogenerators

• High performance piezoelectric nanogenerator was demonstrated by forming a ZnO p-n homojunction with phosphorus-doped p-ZnO the n-ZnO layers.
• The p-n homojunction effectively reduces excess electrons in ZnO, leading to enhanced output power generation.
• The ITO/Ag/ITO substrate provides good conductivity, transparency, flexibility, and reliability under periodically applied stress.

The performance of zinc oxide (ZnO)-based piezoelectric nanogenerators (PENGs) has been largely limited by piezoelectric potential screening effect due to excess electrons in ZnO. To address this problem, we report here a method that can greatly enhance the performance of ZnO PENGs by reducing excess electrons. We formed ZnO p–n homojunction thin film, composed of unintentionally doped n-ZnO and phosphorus-doped p-ZnO, on the ITO/Ag/ITO(IAI) coated flexible substrate with a low sheet resistance of 3.03 Ω/sq and a high optical transmittance of 88.16%, where were prepared by roll-to-roll sputtering. The fabricated PENG with a p–n homojunction demonstrates the output power up to ~140 μW, which is approximately two orders of magnitude higher than that of the PENG only with ZnO. Besides, the output performance related with the p-ZnO and n-ZnO thickness ratio and the roles of p–n junction formation were also systematically investigated. The results here introduce a new method to further extend performance limit of ZnO-based PENGs.

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