I-layer Thickness Research Articles

How backreflection contributes to light absorption for high-performance radial junction photovoltaics

A robust radial junction (RJ) structure directly constructed upon the surface of a flexible Al foil substrate shows a promising potential to boost wearable and portable applications, where the silicon nanowire (SiNW) supported multilayer has proven beneficial in excellent mechanical stability and sufficient light harvesting. Assigned to the beneficial backreflection contributed by the Al foil, a much larger light current can be achieved than that on glass. While a comprehensive understanding of the light absorption under the backreflection of the substrate remains mainly unexplored. Herein, a straightforward comparison of light absorption of RJ units on Al and glass substrates, within a theoretical framework based on a finite-element simulation, is performed. Then, taking SiNW geometric parameters and i-layer thickness into account, the evolutions of light harvesting and the external quantum efficiency curves are systematically studied. These results indicate that, under the backreflection of the substrate, the light absorption shows a reduced dependency on SiNW geometry and i-layer thickness to some extent, laying a critical basis to establish a simpler/easier fabrication process for high-performance flexible RJ thin film photovoltaics.

Efficient all lead-free perovskite solar cell simulation of FASnI3/FAGeCl3 with 30% efficiency: SCAPS-1D investigation

Hybrid organic–inorganic perovskite solar cells (PSCs) currently receives extensive amounts of focus as one of e main study areas in photovoltaic technology, despite its significant progress and high efficiency; the PSCs face numerous issues, such as stability over time and toxic effects of lead. Recently, to address the problem of toxicity, FASnI3 is commonly used to be an absorber in perovskite solar device due to its promising performance. During this article, we formed and modeled a lead-free n-i-p perovskite solar device made of FASnI3 on i-layer and FAGeCl3 for a p-layer, FASnI3 in the n-layer using the simulator SCAPS-1D. To gain better understanding of this solar cell, various parameters impacting the device performance including thickness and doping level of i-layer, n-layer and p-layer thickness, the total i-layer density of defect and the impact of the temperature on the efficiency of device, are investigated and discussed. This new study is interesting since we added a thin layer of FASnI3 that was strongly n-doped to achieve great performance. The importance and effect of n+-FASnI3 on the device performance were showed and discussed. The efficiency of the device has been demonstrated to be affected by both the thickness and doping level of the extra layer n+-FASnI3. The Voc of the concerned device was increased to 1.1 V after adding n+-FASnI3 layer, the current density Jsc increased to 31.42 mA/cm2, the Fill Factor up to 87.33%, after including n+-FASnI3 into the PSC, a high efficiency of 30.19% can be obtained. These simulation results will allow it achievable to develop and manufacture, high-efficiency, with no-lead PSCs.

Self-powered deep ultraviolet PIN photodetectors with excellent response performance based on Ga2O3 epitaxial films grown on p-GaN

PIN-type self-powered deep ultraviolet (DUV) photodetectors (PDs) based on Ta doped n-Ga2O3/i-Ga2O3/p-GaN structures with different i-Ga2O3 layer thicknesses were prepared. In the structure, a Ta element in the doped Ga2O3 epitaxial layer should be substitutional doping, which can be confirmed by time-of-flight secondary ion mass spectrometry. With increasing thickness (0–90 nm) of the i-Ga2O3 layer, the crystal quality of the deposited epitaxial films is gradually improved, but the performance of corresponding PDs does not increase monotonically. The PD with an i-layer thickness of c.30 nm under zero bias shows the best response performance such as maximum photoresponsivity (8.67 A/W), good detectability (1.08 × 1014 Jones), and fast response/decay time (86/50 ms) under 222-nm-UV-light illumination. Such good performance should be attributed to the competition between the high photogenerated carriers and the low electric field, whereas the competition is caused by broadening of the depletion region. This research provides an improved and easy method for fabricating high-performance self-powered DUV PDs.

Model development of lattice-matched p-GaInP/i-GaAs/n-GaInP hetero-junction solar cell and its performance optimization

We report an analytical model for our proposed lattice-matched hetero-junction p-GaInP/i-GaAs/n-GaInP solar cell with the incorporation of AlInP cap layer and MgF2/TiO2 anti-reflection region supported by numerical data obtained using SENTAURUS TCAD. We investigate the impact of intrinsic layer thickness, cap layer thickness, compositional variation of gallium in GaInP alloy used in p- and n-regions of pin solar cell and also studied the effect of indium tin oxide (ITO) anode contact on photovoltaic performance of solar cell in terms of performance matrices i.e., open circuit voltage (Voc), short circuit current density (Jsc), fill-factor and power conversion efficiency (PCE). Also the performance of the proposed solar cell is optimized by judiciously choosing intrinsic layer thickness, and cap layer thickness. Our proposed device featuring 2.1-μm thick i-layer, 156-nm thick cap layer with Ga0.5In0·5P/GaAs active region yields a PCE of 19.89% which turns out to be 67% improvement as compared to the conventional solar cell enabling the proposed design attractive for photovoltaic applications.

Role of doping concentration, thickness of intrinsic layer and number of layers of graphene in Graphene-Silicon heterojunction solar cells

Graphene has unique characteristic of zero band-gap. Its electrical properties can be widely tuned by varying the number of layers or by doping as p or n type with different materials. Due to high optical transmittance and zero band-gap, graphene can be used as both, electron, and hole extraction layer. We have simulated n-graphene/Silicon hetero-structure Ag/ITO/n-Graphene/a-Si:H/c-Si(p)/Ag using AFORS (Automat FOR Simulation of HETero structures) software under AM1.5 illumination and power density of 100 mW/cm2. Here, the thickness of a-Si:H i-layer from 0 to 20 nm, the n-type doping concentration of Graphene from 1 × 1010cm−3 to 1 × 1020cm−3 to get the optimized results. Corresponding to that, we studied the band diagram and hence barrier height, Quantum efficiency etc. The best power conversion efficiency obtained is 18.59% where the Voc is 611.8 mV, Jsc is 37.04 mA/cm2 and FF is 82.03% corresponding to i-layer thickness 5 nm, single layer graphene and n-type doping concentration of 1 × 1020cm−3.

Improved radiation resistance of flexible GaInP/GaAs dual junction solar cell by optimizing GaAs subcell i-layer

The radiation effects of flexible GaInP/GaAs solar cells under 1 MeV electron irradiation have been studied. GaAs subcell intrinsic layer thickness showed remarkable effects on the solar cell radiation resistance. Based on the integrated current density of subcells, GaAs is determined as the current-limiting subcell before and after irradiation regardless to the i-layer thickness, while GaInP subcell exhibits superior radiation resistance. For 1.5 × 1015 e/cm2 irradiation fluence, the remaining factors of maximum output power are 71.94%, 82.53%, and 82.38%, for GaInP/GaAs solar cells with 0, 0.6 μm, 1.0 μm thick i-layer, respectively. EQE spectra of GaAs subcell degraded more in long-wavelength area, due to the higher defect concentration in the base layer. The flexible GaInP/GaAs dual junction solar cell with 0.6 μm thick i-layer sample exhibited an initial conversion efficiency of 23.79%, and the remaining factor is 82.51% after 1.5 × 1015 e/cm2 fluence electron irradiation.

High Power 10–18 GHz Monolithic Limiter Based on GaAs p-i-n Technology

Herein, based on a rounded rectangle p-i-n diode with the minimum radius allowed by the process and a 0.8- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }\mathbf {m}$ </tex-math></inline-formula> thick I-layer, a high-power wideband monolithic limiter was realized by using GaAs p-i-n process. At 16 GHz, the maximum handling power of the monolithic limiter is up to 400 W (56 dBm), while the output power is less than 45 mW (16.5 dBm). Meantime, the insertion loss of the limiter is less than 0.55 dB and the return loss is better than −15 dB in the frequency range of 10–18 GHz, which has little effect on the signal of the receiver. It demonstrates that the limiter has a significant potential in high-frequency and high-power phased-array radars and communication systems.

Simulation of Solar Cell Device Performance Based on Hydrogenated Microcrystal Silicon (µc-Si:H) With Finite Element Method (FEM)

The structure and thickness of the solar cell device layer have a big impact on how well the solar cell works. There for, the aim of this study was to examine how hydrogenated microcrystalline silicon solar cells’ thickness and device structure affected how well they work. Simulation or modeling of the structure in one dimension (1D) is used for the analysis. MATLAB programming was used to analyze the simulation result. The optical band gap changes due to the influence of the structure, therefore the thickness of the p-, I, and n layers are kept constant at 250 Å, 9000 Å, and 250 Å respectively. The results showed that the maximum performance is obtained at the optical band gap, Eci = 1,39 eV, and the resulting power is 0.063465 Watt. Whereas in the simulation of the effect of the thickness on the i-layer, the optical band gap is set to a constant value of Eci = 1,4 eV, while the thickness of the p-layer and n-layer is set to 250 Å. The results also indicate that the maximum performance is at the i-layer thickness of 9000 Å and the power generated is 0.063364 Watt.

Investigation of characteristics of GaAs/AlGaAs p-i-n connecting tunnel diodes

Current-voltage and capacitance-voltage characteristics of tunnel diode structures with GaAs-n++/i-GaAs/i-Al0,2Ga0,8As/Al0,2Ga0,8As-p++ active region and i-layer thicknesses of 7.5 nm and 10 nm and epitaxial growth temperature of 450 °C and 500 °C have been studied. The tunnel diode structures grown by the molecular beam epitaxy technique are intended for application as connecting elements in multijunction photovoltaic converters of high-power monochromatic optical radiation. According to the results obtained, the peak tunnel current density of up to 200 A/cm2 is achieved. Forward current-voltage and capacitance-voltage characteristics of tunnel p-i-n diode structures were measured at room temperature. The capacitance-voltage characteristics of the tunnel diodes being tested were obtained experimentally with the frequency dependence of S-parameters simulated within 10-1000 MHz at bias voltages of 0.4–1 V.

Fabrication of high quantum efficiency p-i-n AlGaN detector and optimization of p-layer and i-layer thickness

In this paper, the fabrication process and structure of AlGaN based p-i-n photodetectors with different layer thicknesses are described. The maximum external quantum efficiency (EQE) of back illumination is 87.87% at zero bias. According to the Poisson equation, the electric field distribution of the devices is analysed, and a detailed method to estimate the reverse bias voltage required for the p-layer and i-layer to be completely depleted is proposed. The reliability of the method is also well proven by the responsivity measurement results under zero bias and reverse bias. Finally, based on the experimental data and theoretical calculation, the optimization method of p-layer and i-layer thickness in p-i-n photodetector is analysed.

Performance of 5-[formula omitted]m PIN diamond diodes as thermal neutron detectors

Diamond PIN diodes with an approximately 5-μm thick i-layer and coated with a thin boron nitride (BN) layer have been tested with a thermal neutron beam. For a flux of 4.4 × 106 n/s/cm2, count rates were on the order of 30–100 counts per second depending on the thickness of the BN neutron converter layer. Pulse height spectra showed features associated with α and 7Li fission products consistent with the thickness of the BN layer. An irradiation test with a 1 MeV neutron equivalent fluence of 1015 n/cm2 showed no significant alteration in the count rate of the tested detector.

Performance Study of the Micromorph Silicon Tandem Solar Cell Using Silvaco TCAD Simulator

This paper is concerned with the numerical modelling of a micromorph silicon tandem solar cell (a-Si:H/µc-Si:H), under series (two-terminal: 2T) and independent (four-terminal: 4T) electrical connection. The study is performed using the simulation software Silvaco TCAD. Both the initial (un-degraded or annealed) state, and the light induced degradation one (well-known Staebler–Wronski effect in a-Si:H) are considered for the studied solar cell, operating under the standard global solar spectrum (AM1.5G). The 2T- and 4T-device optimization is carried out under the effects of the intrinsic (i)-layer thickness of the two sub-cells, and the free carrier mobilities through these layers. By increasing the i-layer thickness of the two sub-cells, the 2T-micromorph tandem cell reveals an optimal conversion efficiency $$\eta$$ of 10% and 7.77% corresponding, respectively, to the initial and degraded states. The 4T-configuration exhibits a relatively better $$\eta$$ of 10.94% at initial state, reduced only to 9.59% at the degraded one. Further improvement of the 2T and 4T-cell output parameters is obtained by increasing the free carrier mobilities, particularly through the top-cell i-layer. By this way, the better $$\eta$$ is also ensured by the 4T-device, which displays an initial state- $$\eta$$ of 12.31%, reduced only to 11.43% at the degraded state. However, the improved efficiencies reached by the 2T-configuration are 11.87% and 10.41% corresponding, respectively, to the initial and degraded states.

Mixed-Phase nc-SiOX:H Interlayer to Improve Light Trapping and Shunt Quenching in a-Si:H Solar Cell

By using radio frequency plasma enhanced chemical vapor deposition method (13.56 MHz), a mixed phase nanocrystalline silicon oxide (nc-SiOX:H) interlayer has been developed. The optoelectronic properties of the nc-SiO:H layer was optimized by varying gas flow ratio. An interlayer has been inserted between the silicon layer and back contact. The nc-SiO:H interlayer has served as a dual-function layer in the solar cell, i.e., act as a rear reflector layer for light trapping and also minimized the local leakage and quenching the shunt effect. The fabricated solar cells with and without nc-SiOX:H interlayer showed efficiencies of 7.84% and 9.35%, respectively, with an i-layer thickness of 250 nm. Efficient light trapping and suppressed parasitic losses by adopting nc-SiOX:H interlayer resulted in a relative increase in the efficiency of about 19.26%. Light-induced degradation study of the solar cells with and without an interlayer has also been presented here. After shunt quenching effect, the relative degradation in conversion efficiency for an interlayer cell is ∼7.27% after 1000 h of light soaking, whereas, under the same experimental conditions, the relative degradation is ∼10.82% for the solar cell without an interlayer. The possible origin of higher degradation in the latter device has been addressed in this work.

A 4.5 [formula omitted]m PIN diamond diode for detecting slow neutrons

The response of a PIN diamond diode with a 4.5 μm thick i-layer to α-particles from a 210Po radioactive source has been measured and compared to the response from a 300 μm thick single crystal type IIa diamond. The results show that this PIN diamond diode with thin i-layer can be employed to detect slow neutrons following absorption on a converter boron layer. Such a detector will operate at low voltages and be rather insensitive to gamma background and neutron radiation damage.

Low-Temperature Growth of Amorphous Silicon Films and Direct Fabrication of Solar Cells on Flexible Polyimide and Photo-Paper Substrates

Direct deposition of hydrogenated amorphous silicon (a-Si:H) thin films and fabrication of solar cells on polyimide (PI) and photo-paper (PP) substrates using a rf-plasma-enhanced chemical vapor deposition technique is reported. Intrinsic amorphous silicon films were deposited on PI and PP substrates by varying the substrate temperature (Ts) over 70–150°C to optimize the deposition parameters for best quality films. The films deposited on both PI and PP substrates at a temperature as low as 70°C showed a photosensitivity (σph/σd) of nearly 4 orders of magnitude which increased to 5–6 orders of magnitude when the substrate temperature was increased to 130–150°C. The increase in σph/σd is due to the presence of a few nanometer-sized crystallites embedded in the film. Solar cells (n-i-p) were fabricated directly on PI, PP and Corning 1737 glass (Corning) at 150°C for different thicknesses of an intrinsic amorphous silicon layer (i-layer). With the increase in i-layer thickness from 330 nm to 700 nm, the solar cell efficiency was found to increase from 3.81% to 5.02% on the Corning substrate whereas on the flexible PI substrate an increase from 3.38% to 4.38% was observed. On the other hand, in the case of cells on PP, the i-layer thickness was varied from 200 nm to 700 nm and the best cell efficiency 1.54% was obtained for the 200-nm-thick i-layer. The fabrication of a-Si (n-i-p) solar cells on photo-paper is presented for the first time.

Effect of Intrinsic Layer Energy Gap and Thicknesses Optimization on the Efficiency of p-i-n Amorphous Silicon Solar Cell

morphous silicon solar cells with single p-i-n layer were grown on 10 cm 2 ITO coated glass substrates. Fabrication process done by using 13.56 MHz RF-Plasma Enhanced Chemical Vapor Deposition (PECVD). Hydrogen flow on the deposition process is widely known to enable the passivation of the dangling bond on Silicon bonds. The passivation of dangling bond affects the band gap of each layer and cell performance in the absorption of photon. In the deposition process of intrinsic layer, SiH 4 gas flow is set constant at 2.5 sccm, while variation is done in hydrogen gas flow at 0 sccm – 90 sccm. Energy gaps obtained for p-layer and n-layer are 2.0 eV and 2.2 eV at thickness 64 nm and 36 nm respectively. Optimizations have been done for intrinsic layer which band gaps are 1.4 eV, 1.6 eV and 1.9 eV at thickness 400 nm. The solar cell efficiency was increased from 4.8% to 5.64% based on the band gaps variety. In addition, i-layer thicknesses were also varied from 400 nm, 500 nm and 600 nm. Thicknesses variation shows an increase of 5.78% in the solar cell efficiency.

Improvement in ultra-thin hydrogenated amorphous silicon solar cells with nanocrystalline silicon oxide

Ultra-thin a-Si:H p-i-n solar cell has been proposed as advance to form three-dimensional structures on nano-structured substrates for achieving optically thick and electrically thin solar cells. However, over the years, although extensive studies have been carried out, no high efficiency was achieved yet. We found that not only the short circuit current density (Jsc) decreases, but also the open circuit voltage (Voc) and fill factor (FF) decreases with the reduction of i-layer thickness, which is opposite to the expectation. We investigated the possible root-causes for this unusual phenomenon and speculated the direct recombination of the electrons in the n-layer and the holes in the p-layer by tunneling through the thin i-layer is the main reason for the reduced Voc and FF in ultra-thin solar cells. Furthermore, the absorption in the doped layers is the most critical limitation for ultra-thin silicon solar cell efficiency because the doped layer thickness becomes comparable to the intrinsic layer. To resolve this issue, we used nanocrystalline silicon oxide (nc-SiOx:H) doped layers with a wide bandgap to reduce the parasitic absorption in the doped layers and the highly asymmetric conductivity improves the carrier collection and made a significant improvement in the cell efficiency. We achieved 8.79%, 7.65%, and 5.32% efficiencies with the i-layer thickness of only 70nm, 50nm and 20nm, respectively, which are the highest ones in ultra-thin silicon solar cells.

Peculiarities of photoconversion efficiency modeling in perovskite solar cells

A theoretical approach to photoconversion efficiency modeling in perovskite p–i–n structures is developed. The results of the theoretical modeling are compared with the experiment. Analysis of the experimental data indicated that the surfaces of the perovskite solar cells (SCs) are spontaneously textured, which leads to more effective light absorption and increased photoconversion efficiency. It is established that photoconversion efficiency as a function of i-layer thickness has a maximum in the region 0.3–0.9 μm.

Enhanced Current Collection in 1.7 eV GaInAsP Solar Cells Grown on GaAs by Metalorganic Vapor Phase Epitaxy

Quaternary GaInAsP solar cells with a bandgap of ∼1.7 eV offer an attractive Al-free alternative to AlGaAs solar cells for integration in next generation of III–V multijunction solar cells with five or more junctions. Development of a high quality 1.7 eV solar cell is also highly sought for III–V/Si tandem solar cells. In this work, we systematically investigate the impact of varying base thicknesses and doping concentrations on the carrier collection and performance of 1.7 eV GaInAsP solar cells. The photoresponse of these cells is found to be very sensitive to p-type zinc doping concentration in the base layer. Prototype 1.7 eV GaInAsP n-i-p solar cell designs are demonstrated that leverage enhanced depletion width as an effective method to achieve peak quantum efficiency exceeding 90%. We also show the importance of optimal i-layer thickness as a critical parameter to reduce the drop in fill-factor (FF) due to field-aided collection. Furthermore, we demonstrate substantial improvement in the cell performance when the GaInAsP base layer is grown at 650 °C instead of 600 °C. The best GaInAsP solar cell ( Eg ∼ 1.65 eV) in this study achieved J SC of 21.1 mA/cm2, V OC of 1.18 V, FF of 83.8%, and an efficiency of 20.8 ± 1% under AM1.5D spectrum (21.5 ± 1% under AM1.5G spectrum). These results highlight the potential of Al-free GaInAsP solar cells for integration in the next generation of III–V multijunction solar cells.

High Voltage Diodes in Diamond Using (100)- and (111)- Substrates

We present a comparative study of PIN structures in diamond on type IIa (100)- and type IIb (111)- oriented bulk diamond substrates. An 8.5- $\mu \text{m}$ thick i-layer demonstrated a blocking voltage>1kV for the (100)-oriented diamond sample without any mesa isolation, passivation, or edge termination structures. PIN diodes with a 530nm thick drift region, on the (111)- sample, demonstrated a blocking voltage of 207V at a current level of 1A/cm2 with a corresponding blocking electric field of 3.9MV/cm. A deep ultraviolet light emission was observed only in (111)-diodes under forward bias, confirming well-behaved p-n junction characteristics in (111) as compared to (100).