Study On Pressure-Regulated Photoelectric Properties Of Iodine And Its Typical Compounds

Photodetector is a kind of photoelectronic device which can convert the input optical signal into electrical signal through different physical mechanisms.It has an extensive application prospect in daily life and military field.Along with the development of society,people’s demand for photodetectors with higher responsiveness,detection sensitivity and wider spectral response range is increasingly urgent.Constantly exploring novel photoelectric functional materials and developing new strategy for modifying photoelectric performance is the key to solving these problems.As an effective external stimulus for regulating the crystal structure and electronic configuration of materials,high pressure could change the value and type of bandgap,which provides a potential new means to develop direct bandgap semiconductor materials more suitable for photoelectric applications and expand the spectrum response range of materials.Relevant theoretical and experimental investigation have confirmed that high pressure could significantly improve the photoelectric and thermoelectric properties of materials,such as significant enhancement in photocurrent by orders of magnitude,induction of inverse photoconductivity and significantly improving the thermoelectric conversion efficiency.Combining the photothermal conversion process and the thermoelectric effect,the photothermoelectric effect can achieve the self-driven and broadband photoresponse under zero bias.However,whether we can expend the spectral response range of materials and self-driven photodetection under zero bias via high pressure strategy,and construct photoelectric/thermoelectric composite system can be constructed under high pressure,are still the new fields to be explored.Iodine and its typical compounds,including alkali metal iodide,layered iodide,iodide perovskite,etc.,not only have the rich high-pressure research background,but also represent and reference among similar materials with high basic research value.Meanwhile,owing to their superb chemical and physical properties,they exhibit the potential application prospects in the fields of radiation detection,solar cells,photoelectric detection,etc.In this paper,we adopt high-pressure strategy to regulate the photoelectric properties of layered semiconductor iodine and its typical compounds Cs I₃,PbI₂ and Cs₃Bi₃I₉,and successfully achieve the significant enhancement in photocurrent,extension of spectral response range and even self-driven photoresponse under zero bias,providing some new insights for developing novel photoelectric functional materials.The main research contents and results are as follows:1.We first put forward a new strategy to extend the spectral response range and enhance photoelectric properties of functional materials via high pressure.And it has been successfully applied to the regulation of photoelectric properties in a layered semiconductor iodine.The maximum photocurrent reaches 4 orders of magnitude higher than the initial value under an illumination of visible-light.Impressively,the spectral response range of iodine was successfully extended to near infrared light（1064nm）with applying pressure and the photoresponse properties were significantly enhanced with further compression.The dramatically enhanced photoelectric activities are attributed to the charge delocalization as well as the increased charge density in the region between the parallel molecules due to the pressure-induced charge-transfer of iodine molecules.These findings can be extended to modify the spectral response range and enhance photoelectric properties of more functional materials.2.Bandgap and type of optical transition are the important factors to determine the functionalities and applications of photoelectric materials.We report giant pressure-enhanced photocurrents and extended detection bandwidth by pressure-regulated indirect-direct bandgap transition in hypervalent Cs I₃.Increasing the photocurrent by almost five orders of magnitude was achieved under visible light illumination.Impressively,detection bandedge shows a successively red shift from visible-light to1650 nm upon compression and the photoelectric properties are significantly enhanced as well.Meanwhile,high pressure conduces to the Cs I₃ operated at ultra-low bias input.Thorough high-pressure spectroscopy with the theoretical calculations suggest that the modifications of photoelectric properties of Cs I₃ are associated with the enhancement of I-I interaction along the quasi endless linear chain directions under compression.This finding offers an effective bandgap engineering strategy for achieving the broadband spectral response and high gain with ultra-low bias in photoelectric detectors.3.Photoelectric devices based on photothermoelectric（PTE）effect show a promising prospect for broadband detection without an external power supply.Herein,we report the significantly enhanceed photoresponse properties of PbI₂ generated from PTE mechanism via high-pressure strategy.The PbI₂ exhibits stable,fast,self-driven and broadband photoresponse up to 980 nm.Intriguingly,the synergy of photoconductivity and PTE mechanism is conducive to enhancing the photoelectric properties and extending detection bandwidth to optical communication waveband（1650 nm）with an external bias.The dramatically enhanced photoresponse characteristics are attributed to the narrowing of the bandgap and significantly decreased the resistance,which originated from the enhancement of atomic orbital overlap owing to pressure-induced Pb-I bonds contraction.These findings open up a new avenue towards designing self-driven and broadband photoelectric devices.4.The use of pressure-induced material amorphous is expected to achieve lower thermal conductivity,thus contributing to higher thermoelectric conversion efficiency.We selected the halide perovskite Cs₃Bi₂I₉,which is accompanied by continuous bandgap reduction during pressure-induced amortization,as the research object,and achieved the superior and tunable photoelectric properties its pressure-induced amorphization process.With increasing pressure,the photocurrents with Xenon lamp illumination exhibit the rapid increase and achieve almost five orders of magnitude increment in comparison with its initial value.Impressively,the broadband photoresponse from 520 to 1650 nm with optimal responsivity of 6.81 m A/W and fast response time of 95/96 ms at 1650 nm was achieved upon successive compression.The high-gain,fast,broadband,and dramatically enhanced photoresponse properties of Cs₃Bi₂I₉ are result of comprehensive the photoconductive and photothermoelectric mechanism,which are associated with enhanced orbital coupling caused by increase of Bi-I interactions in the[Bi I₆]^3-cluster,even in the amorphous state.And the thermal conductivity of Cs₃Bi₂I₉ is significantly reduced owing to the pressure-induced amorphous,which results in higher photothermal-electric conversion efficiency.These findings provide new insights for further exploring potential properties and applications of amorphous perovskites.