Photoconductive multi-layer graphene photodetectors fabricated on etched silicon-on-insulator substrates

Recently, graphene-based photodetectors have been rapidly developed. However, their photoresponsivities are generally low due to the weak optical absorption strength of graphene. In this paper, we fabricate photoconductive multi-layer graphene（MLG） photodetectors on etched silicon-on-insulator substrates. A photoresponsivity exceeding 200 A·W-1is obtained, which enables most optoelectronic application. In addition, according to the analyses of the high photoresponsivity and long photoresponse time, we conclude that the working mechanism of the device is photoconductive effect. The process of photons conversion into conducting electrons is also described in detail. Finally, according to the distinct difference between the photoresponses at 1550 nm and 808 nm, we estimate that the position of the trapping energy is somewhere between 0.4 e V and 0.76 e V, higher than the Fermi energy of MLG. Our work paves a new way for fabricating the graphene photoconductive photodetectors.

Out-of-plane photoconductive and bulk photovoltaic effects in two-dimensionalα-In_(2)Se_(3)/Ta_(2)NiS_(5) ferroelectric heterojunctions

Two-dimensionalα-In_(2)Se_(3)exhibits simultaneous intercorrelated in-plane and out-of-plane polarization,making it a highly promising material for use in memories,synapses,sensors,detectors,and optoelectronic devices.With its narrow bandgap,α-In_(2)Se_(3)is particularly attractive for applications in photodetection.However,relatively little research has been conducted on the out-of-plane photoconductive and bulk photovoltaic effects inα-In_(2)Se_(3).This limits the potential ofα-In_(2)Se_(3)in the device innovation and performance modification.Herein,we have developed anα-In_(2)Se_(3)-based heterojunction with a transparent electrode of two-dimensional Ta_(2)NiS_(5).The out-of-plane electric field can effectively separate the photo-generated electron-hole pairs in the heterojunction,resulting in an out-of-plane responsivity(R),external quantum efficiency(EQE),and specific detectivity(D*)of 0.78 mA/W,10−3%and 1.14×10^(8)Jones,respectively.The out-of-plane bulk photovoltaic effect has been demonstrated by changes in the short circuit current(SCC)and open circuit voltage(V_(oc))with different optical power intensity and temperature,which indicates thatα-In_(2)Se_(3)-based heterojunctions has application potential in mid-far infrared light detection based on its out-of-plane photoconductive and bulk photovoltaic effects.Although the out-of-plane photoconductive and bulk photovoltaic effects are relatively lower than that of traditional materials,the findings pave the way for a better understanding of the out-of-plane characteristics of two-dimensionalα-In_(2)Se_(3)and related heterojunctions.Furthermore,the results highlight the application potential ofα-In_(2)Se_(3)in low-power device innovation and performance modification.

Comparative architecture in monolithic perovskite/silicon tandem solar cells

Inorganic-organic metal halide perovskite light harvester-based perovskite solar cells(PSCs)with widely tunable bandgap have achieved rapid growth in power conversion efficiency,which exceeds 25%now.It is deliberated that if a semitransparent solar cell made of wider bandgap materials was placed on top of a narrow bandgap materials-based solar cell such as a silicon solar cell,with proper optical and electrical arrangements,the resultant tandem device consisting of two subcells could more effectively utilize the solar spectrum than a single junction solar cell.In a perovskite/silicon tandem solar cell(PSTSC),a semitransparent PSC with a wider bandgap is placed on top of a narrow bandgap silicon solar cell.The PSC efficiently harvests the higher energy photons in the ultraviolet and visible regions of the solar spectrum while the silicon solar cell can convert the photons of the infrared region to power.The PSTSC is proposed as a potential candidate to overcome the Shockley-Queisser limit of single-junction silicon solar cells.Though the theoretical limit of a PSTSC is calculated as~42%,its actual efficiency achieved until now is less than 30%.Therefore,a great scope of research exists in improving the efficiency of PSTSCs.Current issues of stability and upscaling of the device in PSCs are also a matter of concern for PSTSCs.A tandem device consists of multiple parts,and different configurations can be applied,thus tuning the architecture of the device.Altering various parts may result in significant changes in the efficiency of the device.In this review,competing architectures of otherwise comparable devices are compared in terms of photovoltaic properties.Thus,future directions to improve the efficiency of the device based on architecture design are proposed herein.In particular,the influence of the polarity of PSCs and the surface morphology of silicon solar cells(both front and rear)on determining the properties of the PSTSC are discussed.