Junction Silicon Solar Cells Research Articles

Ag:PSS polyelectrolyte/PTB7 bilayers as efficient hole transport layers for perovskite solar cells

By virtue of the exceptional optical and electrical features of organic-inorganic lead-halide perovskites, the power conversion efficiency (PCE) of perovskite solar cells (PeSCs) has surpassed that of commercialized single junction silicon solar cells. Although PeSCs have demonstrated exceptional efficiency, there is still room for improvement to approach the theoretical Shockley-Queisser limit. Additionally, there is a need for the development of cost-effective strategies to produce high-performance devices, enabling PeSCs to fulfill their potential as a widely adopted and sustainable energy source.Considering this, in this work, we’ve developed a polyelectrolyte (silver poly(styrene sulfonate (PSS)) (Ag:PSS) hole transport layer (HTL), and investigated it in combination with a conjugated polymer,poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]-dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) as a bilayer HTL. Ag:PSS alone performs poorly due to mismatched energy levels at the anode interface, however, when PTB7 is used in combination with Ag:PSS, effective extraction and transport of carriers towards the anode is achieved. PeSCs with optimized bilayer HTLs (Ag:PSS/PTB7) gave PCEs of up to 17.09 %, higher than that of the Ag:PSS alone (reference device 12.13 %) which can be attributed to improved interfacial energetics at the HTL/perovskite interface.

Influence of Wavelength on the Diffusion Capacitance of a Serial Vertical Junction Silicon Solar Cell in Frequency Regime

Influence of Wavelength on the Diffusion Capacitance of a Serial Vertical Junction Silicon Solar Cell in Frequency Regime

AC back surface recombination, as applied to determine (p) base thickness of both conventional and vertical series junction (n+/p/p+) silicon solar cells under white illumination

AC back surface recombination, as applied to determine (p) base thickness of both conventional and vertical series junction (n+/p/p+) silicon solar cells under white illumination

Influence of the Wavelength on the Series and Shunt Resistances of a Polycrystalline Silicon Solar Cell n+-p-p+ in Frequency Modulation

<p>A study of the illumination wavelength effect on the series and shunt resistances of a serial vertical junction silicon solar cell in frequency modulation is done. From the continuity equation of the minority carriers’ density, the expressions of the minority carriers’ density, the photocurrent density, and the photovoltage, are determined. The curves of the I-V characteristic permit us to deduce the series and shunt resistances, which depend on the wavelength and frequency modulation. A few values of series and shunt resistances in short and long wavelengths are determined respectively at the open circuit and the short circuit situation.</p>

Nature of contaminants introduced in silicon wafers during molecular beam epitaxy chamber annealing

Epitaxial monolithic III–V/Si tandem solar cells are one of the most promising technologies to be adopted by the industry after the efficiency of the current market dominating single junction silicon solar cell saturates at its fundamental limit. One of the key limitations of this technology is the degradation of silicon wafers during in situ annealing in the molecular beam epitaxy chamber. Determining the nature of contaminants in this process is key to improve the efficiency of epitaxial tandem solar cells. However, to date, the nature of contaminants from molecular beam epitaxy chambers remains unknown. In this work, we use photoluminescence imaging, lifetime spectroscopy, and deep level transient spectroscopy to measure the electronic properties of extrinsic impurities incorporated during annealing in the molecular beam epitaxy chamber. Photoluminescence images reveal that at least two impurities diffuse into silicon wafers during molecular beam epitaxy annealing. One is highly localized, while the other one is distributed uniformly across the whole wafer. Phosphorus diffusion is found to confine the localized impurity within the diffused layer but is ineffective at preventing the indiffusion of other impurities. Lifetime spectroscopy shows that metastable impurities with characteristic similar to Cr and CrB in our molecular beam epitaxy annealed silicon wafers. No evidence of Fe or FeB was observed. The emission rates and concentrations of the electrically active defects were measured with deep-level transient spectroscopy: The emission rates of detected defects do not match that of known Cr-related defects.

Status and challenges of multi-junction solar cell technology

The ongoing energy transition to curb carbon dioxide emissions and meet the increasing energy demands have enhanced the need for integration of renewable energy into the existing electricity system. Solar energy has been gaining an increasing market share over the past decade. Multi-junction solar cells (MJSCs) enable the efficient conversion of sunlight to energy without being bound by the 33% limit as in the commercialized single junction silicon solar cells. III-V semiconductors have been used effectively in space applications and concentrated photovoltaics (CPV) over the past few decades. This review discusses the working and components of MJSCs at cell level as well as module level for space applications and CPV. The fabrication procedure, material acquirement of MJSCs is analyzed before introducing the current challenges preventing MJSCs from achieving widespread commercialization and the research direction in the future where these challenges can be addressed.

Influence of the Magnetic Field on the Transient Decay of the Density of Charge Carriers in a Silicon Photocell with Vertical Multijunctions Connected in Series Placed in Open Circuit

This study investigates the effect of the magnetic field on the transient density of excess minority charge carriers in the base of a series-connected vertical junction silicon solar cell. The solar cell is presented in open circuit transient operation. The magnetic field through the Laplace force which deflects the photogenerated carriers from their initial trajectory towards the lateral surfaces reducing their mobility, diffusion and conduction, will certainly influence the decay time of the transient regime. The transient density of excess minority carriers in the base is a sum of infinite terms whose decay time of the different harmonics is studied.

Influence of the Magnetic Field on the Diffusion Capacitance of a Serial Vertical Junction Silicon Solar Cell in Frequency Modulation

In this work, a theoretical study of the effect of the magnetic field on the minority charge carrier density and the diffusion capacity of a silicon solar cell with vertical junction in series in dynamic frequency regime, is done. From the relative continuity equation of the minority charge carriers’ density we establish the boundary condition at the junction and the base medium. The expression of the density of minority carriers of charges in the base, allows us to determine the capacity of diffusion of the solar cell according to the magnetic field, the frequency of modulation, the wavelength of illumination and a junction recombination velocity. The profile of the diffusion coefficient allowed us to make a choice on the values of the magnetic field. These values of the magnetic field intensity will be fixed throughout this article. Each value of the magnetic field strength corresponds to a well-defined value of the resonance frequency. We obtained two ranges of illumination wavelengths from the minority charge carrier’ density profile. The influence of the magnetic field on the diffusion coefficient, of the density of minority charge carriers in short-circuit and open-circuit conditions and of the diffusion capacity, for a specific wavelength, is theoretically studied.

A study of the influence of the base thickness on photoelectric parameters of silicon solar cells with the new TCAD algorithms

he Sentaurus TCAD software package is widely used in the modeling of semiconductor optoelectronic devices. The main part of simulating solar elements is creating a correct geometric model. A geometric model can be built using the SDE module in two different ways, i.e. by writing code or using standard shapes in a graphical environment. Creating complex structures using simple shapes is time-consuming and labour intensive. Therefore, this paper provides data on how to develop algorithms using geometric models of complex structural solar cells. A universal algorithm has been developed for creating a geometric model of solar cells with a sinusoidal p-n junction and a rear multiple structure. Using these algorithms, it is possible to create geometric models of various solar cells from simple to complex structures. By applying this algorithm, the authors studied the dependence of photoelectric parameters of the p-n and n-p junction silicon solar cells on their thickness in order to find the optimum thickness for both structures. It has been found, that the optimum thickness was equal to 256 μm for p-n junction and 75 μm for n-p junction silicon solar cell. The maximum efficiency of p-n junction silicon solar cell is 1.4 times greater than that of n-p junction solar cell in their optimum thickness.

InP/Si High Efficiency Heterojunction-Junction Solar Cell Design Using PSO and the GA Algorithms

This paper presents a single junction solar cell using an Atlas code simulation followed by an optimization using MATLAB software. A noticeable interest occurs in the development of a highly efficient solar cell thanks to its flexibility and lightweight. The INP thin- film solar cell is one of the top qualifiers in the thin- film solar cell market that has a significant power conversion efficiency compared to that of other solar cells. Two algorithms methods are applied on this device in order to get high power conversion efficiency, then the results of each method are compared to the others. In addition, an evaluation is performed to the present junction solar cell by comparing the presented device to similar experimental works. As a result of this paper, an optimization of single junction silicon solar cell, a high short-circuit current density of 43.74 mA/cm2, a maximum open-circuit voltage of 804 mV and a high power conversion efficiency of 30.3% are achieved. The flexibility of the proposed methodology is finally demonstrated and explained.

Temperature Coefficient of Silicon-Based Carrier Selective Solar Cells

Carrier Selective (CS) Silicon solar cells are increasingly explored as a low cost alternative to PN junction Silicon solar cells. While the recent trends on power conversion efficiency are encouraging, the temperature coefficient and hence the power output under elevated temperatures are not well explored for such solar cells. Here, we address this issue through detailed numerical simulations to explore the influence of interface and material parameters on the temperature coefficient. Our results indicate that irrespective of the interface quality, the temperature coefficient of CS solar cells improves with an increase in band discontinuities. Interestingly, contrary to the trends related to efficiency, our results indicate that the temperature coefficient of CS solar cells is more critically affected by the interface quality of the minority carrier extraction layer than the majority carrier extraction layer. These insights have important implications towards the choice of optimal material and processing conditions for Si based CS solar cells.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Radial junction silicon solar cells with micro-pillar array and planar electrode interface for improved photon management and carrier extraction

We demonstrate radial p-n junction silicon solar cells with micro-pillar array with higher short-circuit current and open-circuit voltage than comparable planar silicon solar cells. Micro-pillar array, fabricated by RIE, acts as an effective anti-reflection coating for visible light with less than 6% reflection. Compared to devices with planar surface, devices with micro-pillar array show a 27% enhancement in short circuit current. The radial p-n junction of the micro-pillars also improves extraction probability of the photogenerated carriers, which further increases the short circuit current. Typically, micro-pillar solar cells suffer from high recombination losses at the Si/metal interface, resulting in poor VOC. Our devices prevent these recombination losses by planarizing the Si/metal interface, leading to an open circuit voltage of 622 mV, the highest ever reported for micro-pillar solar cells. This planarized contact also reduces the series resistance associated with radial junctions, leading to series resistance of ≤0.50 Ω-cm2 and fill factors up to 76.7%.

Screen printed, large area bifacial N-type back junction silicon solar cells with selective phosphorus front surface field and boron doped poly-Si/SiOx passivated rear emitter

This paper reports on the effect of screen printed metallization on the passivation quality of a boron doped poly-Si/SiOx passivated contact (PC) structure composed of a very thin Si oxide (∼15 Å) capped with boron doped poly-Si. Our boron doped poly-Si/SiOx passivated contact (p-Poly Si/SiOx PC) with a SiNx capping layer gave excellent surface passivation with a very low saturation current density of ∼5 fA/cm2. After screen printed metallization on poly-Si with a metal coverage of ∼10%, this value increased to ∼17 fA/cm2. This paper also demonstrates the fabrication of screen printed, large area (239 cm2), high efficiency (∼21%) n-base bifacial back junction Si solar cells with p-Poly-Si/SiOx PC on the rear and a phosphorus implanted n++-n+ selective front surface field. Detailed analysis is performed to quantify recombination and extract the saturation current density contributions (J0) from each layer of the cell including the metallized front surface field and the tunnel oxide passivated contact. Finally, 2D device modeling of this back junction cell is performed by implementing a simple approach which replaces the p-Poly-Si/SiOx PC by an equivalent p-n junction with the same J0 and gives a good match between the measured and simulated cell parameters using the extracted J0 and recombination velocity values.

Effect of temperature of a vertical parallel silicon solar cell under photo-thermal conditions

This paper aims presenting the study of the photo-thermal and behavior of the space charge region for an n + −p vertical parallel junction silicon solar cell under monochromatic illumination. It also deals with mathematical relation related to the use of new approach that involves parameter of the solar cell. The study of the base for an illumination by the rear face allowed us to determine the density of the minority carriers, the photocurrent, the photovoltage. Nyquist and Bode’s representation of recombination velocity, angular frequency and impedance allowed us to give their equivalent circuits. Also we studied the thermal behavior of the solar cell through the temperature which is a very important parameter in the operation of the solar cell. We study the influence of the pulsation on the variation of the temperature and the density of heat flux.

Analytical approach for performance estimation of BSPVT system with liquid spectrum filters

The terrestrial solar spectrum is not monochromatic; it consists of ultraviolet, visible and infrared radiations. The most commonly used single junction silicon solar cell responds to the visible and near infrared part of the solar spectrum. The ultraviolet and the infrared part of the solar spectrum causes thermal losses in the solar cell, thus reduces its electrical conversion efficiency. In order to reduce these thermal losses, and to improve the conversion efficiency of the solar cells, the concept of spectrum filtration is introduced. Use of liquid spectrum filters for photovoltaic thermal systems (PVT) is reported in some of the recent literatures. In this technique, the selective liquids are used to filter the incoming solar radiations; the desired solar spectrum for photo electricity is only allowed to enter in. The unfiltered part of the spectrum is used separately as heat for the thermal systems. The system gives heat and electricity simultaneously and it is known as Beam Split Photovoltaic Thermal System (BSPVT). The experimental feasibility of these systems has been reported in recent literatures. In the current article, an analytical approach for the performance estimation of a BSPVT system with liquid spectrum filters is reported. C-Si PV module with three different liquids as spectrum filters viz; water, silicone oil and coconut oil are considered. The mathematical analysis is based on the estimation of radiation attenuation by the liquid spectrum filters. The ‘Transmissivity Absorptivity product (τα)’ of the liquid spectrum filters is determined using Snell's law and Bouger's law. The maximum average thermal and electrical efficiency of the system are estimated as 79% and 14% respectively. The detailed analytical approach is discussed in this article.

Electroluminescence analysis for spatial characterization of parasitic optical losses in silicon heterojunction solar cells

Electroluminescence (EL) coupled with reflection measurements are used to spatially quantify optical losses in silicon heterojunction solar cells due to plasmonic absorption in the metal back contacts. The effect of indium tin oxide back reflector in decreasing this plasmonic absorption is found to increase the reflection from the back nickel (Ni)-aluminum (Al) and Al metals by ∼12% and ∼41%, respectively, in both bifacial and front junction silicon solar cells. Losses due to back reflection are calculated by comparison between the EL emission signals in high and low back reflection samples and are shown to be in agreement with standard reflection measurements. We conclude that the optical properties of the back contact can significantly influence the EL intensity which complicates the interpretation of EL as being primarily due to recombination especially when comparing two different devices with spatially varying back surface structures.

Noise and optical spectroscopy of single junction silicon solar cell

Noise and optical spectroscopy of single junction silicon solar cell

Light intensity and spectral dependence characteristics of silicon nanowire/PEDOT:PSS heterojunctions solar cells

Recently, research on Si/conducting organic polymer heterojunction solar cells has gained prominence owing to their low fabrication cost and potential for reasonably good efficiency. Poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated over n-type Si forms such heterojunction which has theoretical capabilities comparable to the conventional p-n Si junction. However these devices still need fabrication parameters optimization in order to compete with conventional p-n junction silicon solar cells. Here, we report the photoresponse of Ag/PEDOT:PSS/n-SiNW/Al solar cell at different light intensities and different wavelengths. The device is fabricated by spin coating the PEDOT:PSS over n-Si NW based Si substrates. It is further noted that the short circuit current is significantly lower in J-V response than that derived from external quantum efficiency measurements. It is observed that the photocurrent density and fill factor deteriorates significantly at higher intensities. This is suggestive of some space charge build up at Si-PEDOT:PSS interface at higher intensities because of difference in hole mobility in Si and PEDOT:PSS. This could also be strongly attributed to structural changes in the PEDOT:PSS layer which might change the charge carrier dynamics and hence the electrical response of the layer. The response of cell with varying intensity can help to optimize the illumination condition for the cell. The wavelength response of the cell can help us better understand the solar cell working and can help in optimizing the fabrication parameters. This opens up new area of intensive research required in order to optimize polymer layer properties and improving the performance of PEDOT:PSS/SiNW-based solar cell.

Low temperature perovskite solar cells with an evaporated TiO2 compact layer for perovskite silicon tandem solar cells

Silicon-based tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Perovskite solar cells are particularly promising as a top cell in monolithic tandem devices due to their rapid development towards high efficiencies, a tunable band gap with a sharp optical absorption edge and a simple production process. In monolithic tandem devices, the perovskite solar cell is deposited directly on the silicon cell, requiring low-temperature processes (< 200°C) to maintain functionality of under-lying layers of the silicon cell in case of highly efficient silicon hetero-junction (SHJ) bottom solar cell. In this work, we present a complete low-temperature process for perovskite solar cells including a mesoporous titanium oxide (TiO2) scaffold - a structure yielding the highest efficiencies for single-junction perovskite solar cells. We show that evaporation of the compact TiO2 hole blocking layer and ultra-violet (UV) curing for the mesoporous TiO2 layer allows for good performance, comparable to high-temperature (> 500°C) processes. With both manufacturing routes, we obtain short-circuit current densities (JSC) of about 20 mA/cm², open-circuit voltages (VOC) over 1 V, fill factors (FF) between 0.7 and 0.8 and efficiencies (η) of more than 15%. We further show that the evaporated TiO2 layer is suitable for the application in tandem devices. The series resistance of the layer itself and the contact resistance to an indium doped tin oxide (ITO) interconnection layer between the two sub-cells are low. In addition, the low parasitic absorption for wavelengths above the perovskite band gap allow a higher absorption in the silicon bottom solar cell, which is essential to achieve high tandem efficiencies.