Two-Dimensional Piezoelectric Semiconductor Materials With Coupling Of Piezoelectric And Semiconductor Properties For Optoelectronic Devices

The piezoelectric effect has been generally used in electromechanical actuation,sensing,and energy harvesting,and strain induces piezoelectric charges at mechanical stress in non-centrosymmetry materials.Traditionally piezoelectric materials such as Lead Zirconate titanate and polyvinylidene fluoride(PZT and PVDF)are insulator which is not used for functional electronic/optoelectronic devices.The strain-induced piezoelectric charges used for tuning carriers in piezoelectric materials have been often long overlooked.Semiconductor materials(Zn O,Ga N,and Cd S)of wurtzite or zinc blende structures also have piezoelectric properties,but not as widely utilized in piezoelectric actuators and sensors like PZT because of the rather little piezoelectric coefficients.Two dimensional(2D)piezoelectric semiconductors are 2D materials that have both piezoelectric and semiconductor properties.These materials have a non-centrosymmetric structure,which shows high potential in nanoscale,electromechanical frameworks,and optoelectronic gadgets.There is a developing enthusiasm for these 2D piezoelectric semiconductor materials in optoelectronics gadgets,energy harvesting,and electronics.Owing to the coupling between piezoelectricity,semiconductor,both device applications,and novel fundamental phenomena potential emerges,therefore this relative research cause a new field of piezotronics and piezo-phototronics.The fundamental principle of piezotronics and piezo-phototronics lies in the fact that strain-induced polarization charges introduced at the interface can effectively regulate the local potential barrier height and enhance the charge carrier transport across local junctions/contacts by exhibiting substantial influence on the concentration distribution of free carriers and interfacial electronic charged states in the applied devices.The basic physics principles guiding piezotronics and piezo-phototronics are employed in this dissertation.Functional electronic/optoelectronic devices based on two-dimensional piezoelectric semiconductor materials couple with piezoelectric and semiconductor properties are presented to demonstrate the applications of the piezotronic and piezo-phototronic effects,including piezo-phototronic single-junction solar cell and piezo-phototronic multijunction solar cell.Here we introduced a piezo-phototronic multijunction solar cell by utilizing a framework based on single-type two-dimensional piezoelectric semiconductor materials.The performance parameters such as open circuit current density,fill factor,open-circuit voltage,etc,of the proposed piezo-phototronic multijunction solar cell was looked at by using the detailed balance limit principles.The findings suggest that the energy conversion efficiency of the proposed piezo-phototronic multijunction solar cell potentially exceeds 33 percent when subjected to 6000 K temperature of a blackbody.Also,the obtained conversion efficiency surpasses the well-known theoretical Shockley Queisser limit.Most recent studies have shown that group(IV)monochalcogenides have a higher piezoelectric constant in comparison with those predicted values in two-dimensional(2D)materials.The materials properties for piezo-phototronic solar cell based on this two-dimensional semiconductor were theoretically investigated.Also,the performance parameters of 2D piezo-phototronic single-junction solar cells have been studied by utilizing monolayer group(IV)monochalcogenides such as Sn Se,Sn S,Ge S,and Ge Se metal-semiconductor contact.The modulation ratio by piezoelectric charges has been investigated under applied external strains.The piezo-phototronic effect plays a key role in the enhancement of the performance of solar cells.Third generation semiconductors,including Zn O and Ga N,have comparatively broad spontaneous polarization in their longitudinal path of the nanowires based on the asymmetric arrangement in their c-axis direction.Two-way or multiway couplings of piezoelectric,photoexcitation,and semiconductor properties have created new research areas,such as piezotronics and piezo-phototronics.Besides,we present the performance and material properties of third-generation semiconductor solar cells using a piezo-phototronic effect.The characteristics of current-voltage open-circuit voltage,maximum output power,fill factor and power conversion efficiency of the piezo-phototronic solar cell have been examined.The degree of modulation of the piezo-phototronic impact is presented to determine the output of the applied strain.Among the semiconductor materials of the third generation,the Al N has a noteworthy modulation ratio between Zn O and Ga N.It happens that the modulation ratio of Al N is almost twice as high as Ga N.The study opens a new window to produce the next-generation ultrathin-high efficiency next-generation piezo-phototronic solar cells.This work contributes to understanding how the Piezo-phototronic effect can be applied to regulate the charge carriers' generation,separation,transport,and recombination by controlling the Schottky barrier height of metal-semiconductor contact or built-in potential of the p-n junction.By successfully applying piezo-phototronic effects in a different range of optoelectronic devices,we have shown how these two effects can be utilized in an effective way of modifying the physical properties of charge carriers in piezoelectric semiconductors.