Showing papers in "IEEE Journal of Photovoltaics in 2017"
TL;DR: In this paper, high-efficiency n-type multicrystalline silicon solar cells with diffused boron front emitter and full-area passivating rear contact (TOPCon) are presented.
Abstract: Silicon solar cells featuring the highest conversion efficiencies are made from monocrystalline n-type silicon. The superior crystal quality of high-performance multicrystalline silicon (HP mc) in combination with the inherent benefits of n-type doping (higher tolerance to common impurities) should allow the fabrication of high-efficiency solar cells also on mc silicon. In this paper, we address high-efficiency n-type HP mc solar cells with diffused boron front emitter and full-area passivating rear contact (TOPCon). n-type HP mc silicon was crystallized at Fraunhofer ISE featuring a very high average lifetime in the range of 600 μ s (i.e., diffusion length >800 μ m) after application of all high-temperature steps necessary for cell fabrication. Using a “black silicon” front texture we have achieved a weighted reflectance of ∼1% and simultaneously a very good electrical performance, i.e., J 0 e values of ≤ 60 fA/cm2 for a 90 Ω/sq emitter. The resulting n-type mc silicon solar cells show certified conversion efficiencies up to 21.9%, representing the current world record for mc silicon solar cells.
136 citations
TL;DR: In this article, the authors give an overview on the current understanding of a technologically relevant defect group in crystalline silicon related to the presence of boron and oxygen and provide a consistent nomenclature for defect transitions in order to simplify discussion.
Abstract: This paper gives an overview on the current understanding of a technologically relevant defect group in crystalline silicon related to the presence of boron and oxygen. It is commonly addressed as boron–oxygen defects and has been found to affect silicon devices, whose performance depends on minority charge carrier diffusion lengths—such as solar cells. The defects are a common limitation in Czochralski-grown p-type silicon, and their recombination activity develops under charge carrier injection and is, thus, commonly referred to as light-induced degradation. A multitude of studies investigating the effect have been published and introduced various trends and interpretations. This review intends to summarize established trends and provide a consistent nomenclature for the defect transitions in order to simplify discussion.
122 citations
TL;DR: A fractional-order fuzzy logic control (FOFLC) method for maximum power point tracking in a photovoltaic (PV) system is presented and can improve the tracking accuracy in weather variations compared with the conventional fuzzy MPPT.
Abstract: A fractional-order fuzzy logic control (FOFLC) method for maximum power point tracking (MPPT) in a photovoltaic (PV) system is presented. By combining the robustness of fuzzy logic with the accuracy of fractional order, the proposed method can improve the tracking accuracy in weather variations compared with the conventional fuzzy MPPT. First, the fractional-order factor is carefully selected according to the dynamic range of the fuzzy controller. It takes a bigger alpha factor in the first place to expand the fuzzy domain and shortens the time of searching for the MPP. When the maximum power point is approached, it uses a smaller the alpha factor to contract the fuzzy domain and eliminates the oscillations at the MPP. Therefore, the FOFLC in a PV system has rapid dynamic responses under environment variations and high tracking accuracy of the maximum power point. Second, MATLAB/Simulink software is employed to simulate a PV power system and verify the proposed algorithm by various simulations. The enhanced MPPT algorithm has been implemented on a field programmable gate array (FPGA) board. Finally, a boost dc–dc converter experiment has been carried out to evaluate the system performance. The simulation and experiment results show that this method can improve the transient and steady-state performance simultaneously.
117 citations
TL;DR: In this article, the first fully laser-processed large area perovskite solar module with an aperture ratio of 95% and a power conversion efficiency of 9.3% was reported.
Abstract: Small area hybrid organometal halide perovskite based solar cells reached performances comparable to the multicrystalline silicon wafer cells. However, industrial applications require the scaling-up of devices to module-size. Here, we report the first fully laser-processed large area (14.5 cm2) perovskite solar module with an aperture ratio of 95% and a power conversion efficiency of 9.3%. To obtain this result, we carried out thorough analyses and optimization of three laser processing steps required to realize the serial interconnection of various cells. By analyzing the statistics of the fabricated modules, we show that the error committed over the projected interconnection dimensions is sufficiently low to permit even higher aperture ratios without additional efforts.
108 citations
TL;DR: In this article, a triple-junction GaInP/Al x Ga 1- x As/Si solar cells were fabricated using surface-activated direct wafer bonding, which achieved bulk-like bond strength, high transparency, and conductivity over 4-inch wafer area.
Abstract: Stacking III–V p-n junctions on top of wafer-based silicon solar cells is a promising way to go beyond the silicon single-junction efficiency limit. In this study, triple-junction GaInP/Al x Ga 1- x As//Si solar cells were fabricated using surface-activated direct wafer bonding. Metal–organic-vapor-phase-epitaxy-grown GaInP/Al x Ga1- x As top cells are bonded at low temperature to independently prepared wafer-based silicon cells. n-Si//n-GaAs interfaces were investigated and achieved bulk-like bond strength, high transparency, and conductivity homogeneously over 4-inch wafer area. We used transfer-matrix optical modeling to identify the best design options to reach current-matched two-terminal devices with different mid-cell bandgaps (1.42, 1.47, and 1.52 eV). Solar cells were fabricated accordingly and calibrated under AM1.5g 1-sun conditions. An improved Si back-side passivation process is presented, leading to a current density of 12.4 mA/cm2 (AM1.5g), measured for a flat Si cell below GaAs. The best 4 cm2 GaInP/GaAs//Si triple-junction cell reaches 30.2% 1-sun efficiency.
104 citations
TL;DR: GenPro4 as mentioned in this paper is a new optical model for solar cell simulation, which is suitable for quickly and accurately simulating a wide range of wafer-based and thin-film solar cells.
Abstract: We present a new version of our optical model for solar cell simulation: GenPro4 . Its working principles are briefly explained. The model is suitable for quickly and accurately simulating a wide range of wafer-based and thin-film solar cells. Especially adjusting layer thicknesses to match the currents in multijunction devices can be done with a minimum of computational cost. To illustrate this, a triple junction thin-film silicon solar cell is simulated. The simulation results show very good agreement with external quantum efficiency measurements. The application of an MgF2 antireflective coating or an antireflective foil with pyramid texture is considered. Their effects on the implied photocurrents of top, middle, and bottom cells are investigated in detail.
100 citations
TL;DR: This paper identifies some key technologies toward 24% efficient PERC cells and provides its technology-related target requirements and a method to improve cell efficiency most effectively by monitoring the current losses at the maximum power point.
Abstract: Many manufacturers choose the passivated emitter and rear cell (PERC) approach in order to surpass the 20% cell efficiency level in mass production. In this paper, we study the efficiency potential of the PERC approach under realistic assumptions for incremental improvements of existing technologies by device simulations. Based on the most recent published experimental results, we find that the PERC structure is able to reach about 24% cell efficiency in mass production by an ongoing sequence of incremental improvements. As a guideline for future developments, we provide a method to improve cell efficiency most effectively by monitoring the current losses at the maximum power point. By means of numerical device modeling, we identify some key technologies toward 24% efficient PERC cells and provide its technology-related target requirements.
99 citations
TL;DR: In this paper, the junction resistivity of high quality carrier-selective polysilicon on oxide (POLO) junctions with the transfer length method was investigated and a back-junction back-contact solar cell with p-type and n-type POLO junctions was demonstrated.
Abstract: We investigate the junction resistivity of high-quality carrier-selective polysilicon on oxide (POLO) junctions with the transfer length method. We demonstrate ${{n}}^{+ }$ POLO junctions with a saturation current density $J_{{\rm{C,poly}}}$ of 6.2 fA/cm2 and a junction resistivity $\rho _{{\rm{c}}}$ of 0.6 mΩcm2, counterdoped ${{n}}^{+ }$ POLO junctions with 2.7 fA/cm2 and 1.3 mΩcm2, and ${{p}}^{+ }$ POLO junctions with 6.7 fA/cm2 and 0.2 mΩcm2. Such low junction resistivities and saturation current densities correspond to excellent selectivities $S_{{10}}$ of up to 16.2. The efficiency potential for back-junction back-contact solar cells with these POLO junctions was determined to be larger than 25 % by numerical device simulations. We demonstrate experimentally a back-junction back-contact solar cell with p -type and n -type POLO junctions with an independently confirmed efficiency of 24.25 %.
93 citations
TL;DR: In this article, the atomic layer deposited (Zn,Mg)O second buffer layer and K treatment of the absorber surface were applied to the submodule and both techniques were implemented into the minimodule.
Abstract: New record efficiencies have been achieved on Cd-free Cu(In,Ga)(Se,S)2 thin-film photovoltaic submodules prepared by a two-step sulfurization after selenization process. Aperture area efficiencies of 19.2% and 19.8% were independently confirmed on a 30 cm × 30 cm submodule (841 cm2) and on a 7 cm × 5 cm minimodule (24.2 cm2), respectively. These achievements were brought about by transferring several key techniques, especially atomic layer deposited (Zn,Mg)O second buffer layer and K treatment of the absorber surface, from the fundamental study of small-area cell development. The former technique was applied to the submodule and both techniques were implemented into the minimodule. The (Zn,Mg)O second buffer layer increases transmittance of the window layer and improves junction quality resulting in the reduced interface recombination. The K treatment, which was developed by reference to the postdeposition treatment widely used in the co-evaporation process, significantly enhances open-circuit voltage and fill factor. Several material and device characterizations performed to illuminate the effects of the K treatment showed that increased free carrier concentration and reduced carrier recombination throughout the whole absorber film contributed to the improved performance. Contrary to the conventional postdeposition treatment in the co-evaporation process, significant depletion of Cu at the absorber surface was not observed, which can be attributed to S-rich circumstances of our absorber surface. The achievement of nearly 20% efficiency on the minimodule having identical structure to the production modules ensures further performance improvements in industrial Cu(In,Ga)(Se,S)2 modules in the near future.
93 citations
TL;DR: In this paper, the optical properties of the solar module were redesigned to eliminate parasitic absorption and enhance thermal emission to reduce the operating temperature of one-sun terrestrial solar modules up to 10 °C.
Abstract: For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20–30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of the solar module to eliminate parasitic absorption ( selective-spectral cooling ) and enhance thermal emission ( radiative cooling ). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. This self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.
89 citations
TL;DR: In this article, the authors investigated the influence of the spectral albedo on the power output of bifacial solar cells and found that the ideal band gap and the maximum efficiency depend on the spectrum and intensity of the surroundings and that optimal cell performance cannot be assessed when only accounting for spectrally independent albedos.
Abstract: We have investigated the influence of the spectral albedo on the power output of bifacial solar cells. We adapted the Shockley–Queisser radiative flux balance framework to account for a variation of the spectrum and intensity of the incoming light. We find that the ideal band gap and the maximum efficiency depend on the spectral albedo of the surroundings and that optimal cell performance cannot be assessed when only accounting for a spectrally independent albedo. With a spectral albedo model, we predict that the power output for a bifacial silicon solar cell surrounded by green grass is 3.1% higher than for a wavelength-independent albedo, and even 5.2% higher for white sand. We experimentally verify this trend for silicon heterojunction solar cells and we derive the ideal spectral albedo.
TL;DR: In this article, the P2 interconnection that represents the electrical connection between serially connected cells in a module is optimized for perovskite thin-film photovoltaic modules.
Abstract: This paper reports on the analysis and comparison of mechanical and laser patterning in the fabrication of perovskite thin-film photovoltaic modules. Besides stability, device upscaling and module fabrication is a key challenge for the commercialization of perovskite photovoltaics. Here, the focus is on the optimization of the P2 interconnection that represents the electrical connection between serially connected cells in a module. The specific contact resistivity for P2 interconnection is determined by using an enhanced transmission line method. Mechanical or laser patterning are used to fabricate 4 cm $^{2}$ modules with aperture area efficiencies of up to 15.3% and geometrical fill factors as high as 94%. With the application of a simulation program with an integrated circuit emphasis-based electrical device model, the interconnection losses are quantified, and optimal designs for perovskite modules are presented.
TL;DR: This paper aims at providing a reliable algorithm to identify photovoltaic (PV) series arc faults regardless of complex fault-like interferences and building fusion coefficients, two variables are arithmetically fused to achieve the arc fault discovery.
Abstract: This paper aims at providing a reliable algorithm to identify photovoltaic (PV) series arc faults regardless of complex fault-like interferences Through conducting various arc fault experiments with different PV current levels, arc gap lengths, and load types, PV series arc fault features have been understood comprehensively To avoid unwanted nuisance tripping, fault-like conditions are analyzed to confirm the unique arc fault features Based on the loop current signature, a greater unstable fluctuation in the time domain and extra arc noises in the time-frequency domain are chosen as identification features By quantificational evaluations, optimal detection variables with the Hamming window and the proper time resolution have been established to achieve the best identification results By building fusion coefficients, two variables are arithmetically fused to achieve the arc fault discovery The algorithm could also classify fault-like into normal and adjust the threshold value dynamically to fit different normal current levels Its validity has been verified by experimental results on the simulated platform
TL;DR: In this paper, the authors measured the injection-dependent lifetime throughout degradation and regeneration and performed lifetime spectroscopy at several time points to gain further insight into the root cause of LeTID.
Abstract: While progress has been made in developing engineering solutions and understanding light- and elevated temperature-induced degradation (LeTID) in p -type multicrystalline silicon (mc-Si), open questions remain regarding the root cause of LeTID. Previously, lifetime spectroscopy of multicrystalline silicon (mc-Si) passivated emitter and rear cell semifabricates in the unaffected and the degraded states enabled identification of the effective recombination parameters of the responsible defect. To gain further insight into the root cause of LeTID, in this paper, we measure the injection-dependent lifetime throughout degradation and regeneration and perform lifetime spectroscopy at several time points. Our analysis indicates that the change in lifetime during most of the process can be described by a corresponding change in the concentration of a single responsible defect. We also explore further exposure to light and temperature after nearly complete regeneration and a subsequent dark anneal to demonstrate that the behavior is no longer consistent with LeTID and the same defect is not detected by lifetime spectroscopy at maximum degradation. We consider our results in the context of the proposed hypotheses for LeTID and conclude that both hydrogenation and precipitate dissolution during firing are consistent with our results.
TL;DR: The proposed control strategies are experimentally validated on a three-phase grid-connected photovoltaic inverter system and experimental results show that the control system is effective in terms of voltage and power control with smooth transitions between the modes.
Abstract: A robust feedback linearizing control strategy, based on sliding mode compensation, is proposed for the operation of a grid-connected photovoltaic inverter system under grid faults, characterized by unbalanced voltages, to meet low-voltage ride through requirements. Under normal grid condition, the control system is developed for maximum power transfer from the photovoltaic source to the grid by maximum power point tracking operation of the dc–dc converter, and regulation of the dc-link voltage and the current at the inverter-grid side. Under grid fault, which is unbalanced grid voltage due to voltage dips, the active power is regulated to reduce the current excess and the reactive power is injected to avoid the inverter damage or disconnection, while the dc-link voltage is controlled via the dc–dc converter. A sliding mode compensator is injected into the control system to enhance its robustness to uncertainties. The feedback linearizing control schemes are developed from the grid model at the inverter side and the dc-link model at the dc–dc converter side. The proposed control strategies are experimentally validated on a three-phase grid-connected photovoltaic inverter system and experimental results show that the control system is effective in terms of voltage and power control with smooth transitions between the modes.
TL;DR: This paper aims to provide a quite comprehensive overview of typical defects observed after an extensive flight campaign in North of Italy made by light multicopter unmanned aerial vehicles over different types of PV plants.
Abstract: Nowadays one of the most consolidated inspection methods for photovoltaic (PV) systems is the use of drones. PV modules installed in the last decade show now a quite wide range of defects able to sensibly compromise the performance of the plant. This paper aims to provide a quite comprehensive overview of typical defects observed after an extensive flight campaign in North of Italy made by light multicopter unmanned aerial vehicles over different types of PV plants. The objective of this investigation is to summarize the most observed detectable faults and to give some data of their frequency. Different kinds of sensors have been installed onboard and some peculiarities will be emphasized with respect to the visible, in-field measurements and IR-collected data. The results of this campaign will be discussed in order to provide a clear idea of potential impact of unmanned technology in this sector for future decades.
TL;DR: A reconfiguration technique is presented that finds the optimal configuration in a reduced computational time and utilizes the greedy optimization principle to derive a simple strategy that can find the optimal PV configuration without the need to solve heavy dynamic programming problems.
Abstract: In addition to energy losses produced by mistracking the global power peak, partially shaded PV systems are susceptible to extra power losses due to power mismatch in their series-connected PV modules. Reconfiguring of PV modules in a PV system has been referred to as an effective method for minimizing these losses. Unfortunately, the available reconfiguration methods that are accurate need lengthy computational time to determine the optimal configuration, which impedes their practical realization in large PV systems. In this paper, a reconfiguration technique is presented that finds the optimal configuration in a reduced computational time. Unlike the existing methods, the proposed method utilizes the greedy optimization principle to derive a simple strategy that can find the optimal PV configuration without the need to solve heavy dynamic programming problems. The benefits of the proposed method are verified with respect to the existing methods under various shading scenarios. Furthermore, a case study on a large PV system is conducted demonstrating that the achieved computational time reduction can reduce the mismatch power losses in partially shaded PV systems.
TL;DR: In this article, the authors show that silver substitution for copper in Cu(In,Ga)Se2 (CIGS) to form ACIGS leads to a reduction of the voltage loss expressed as Eg/q − V oc.
Abstract: In this contribution, we show that silver substitution for copper in Cu(In,Ga)Se2 (CIGS) to form (Ag,Cu)(In,Ga)Se2 (ACIGS) leads to a reduction of the voltage loss expressed as Eg/q – V oc. This, in turn, leads to higher device efficiencies as compared to similar CIGS devices without Ag. We report $V_{{\rm{oc}}}$ at 814 mV at a conversion efficiency of 21% for our best ACIGS device with 20% of the group I element consisting of silver. Comparing ACIGS and CIGS devices with the same Ga/(Ga + In) ratio, the ACIGS devices exhibit about 0.05 eV higher bandgap. Alkali postdeposition treatment with KF leads to improvements in efficiency both for CIGS and ACIGS, but we find that the dose of KF needed for optimum device for ACIGS is 10–20% of the dose used for CIGS.
TL;DR: An experimental platform for arc fault of a PV system was built to simulate the DC side parallel arc fault in the PV system and a mixed criterion is proposed to overcome the shortcomings of the above-mentioned criteria.
Abstract: This paper presents the problem of parallel arc fault in the DC side of a photovoltaic (PV) system. First, an experimental platform for arc fault of a PV system was built to simulate the DC side parallel arc fault in the PV system. By extracting the current waveform at the exit of PV panels, a study was conducted on the characteristics of the current during parallel arc fault. The result of Fourier transform on the current suggests that the high-frequency component of the current mainly concentrates in the frequency range of 126–250 kHz. According to the analysis of arc fault characteristic in time domain and frequency domain, reversal current maximum, modulus maximum, and energy are chosen as the criteria to detect parallel arc fault. And finally, a mixed criterion is proposed to overcome the shortcomings of the above-mentioned criteria and its reliability is verified by experiments. It provides a theoretical basis for the detection of the parallel arc fault in the PV system.
TL;DR: In this article, it is observed that boron-doped float-zone silicon coated with hydrogenated silicon nitride shows strong instabilities in effective minority carrier lifetime after a fast firing step and subsequent treatment at elevated temperatures and illumination.
Abstract: In this study, it is observed that boron-doped float-zone silicon coated with hydrogenated silicon nitride shows strong instabilities in effective minority carrier lifetime after a fast firing step and subsequent treatment at elevated temperatures and illumination. During such a treatment, both degradation and recovery features are visible over time scales from minutes to months. To further investigate the observed behavior, corona charging series, capacitance voltage measurements, and chemical repassivation methods are applied. It is shown that a first fast degradation and recovery is associated with changes in the bulk lifetime, and it is observed that the fast firing step strongly influences this bulk instability. A subsequent slower degradation and recovery reflects changes in the effective surface recombination velocity that can be attributed to changes in the chemical passivation quality. It can be concluded that care has to be taken when boron-doped float-zone silicon is used as a supposedly stable high lifetime reference material after a fast firing step. Additionally, it can be stated that a silicon nitride related passivation may be far from stable at elevated temperatures and illumination after a fast firing step.
TL;DR: Field measurements of bifacial modules under natural illumination with proposed indoor test methods, where irradiance is only applied to one side at a time are compared, showing good agreement to indoor measurements, within 1%–2% for power and other current–voltage curve parameters.
Abstract: One-sun power ratings for bifacial modules are currently undefined. This is partly because there is no standard definition of rear irradiance given 1000 Wcm−2 on the front. Using field measurements and simulations, we evaluate multiple deployment scenarios for bifacial modules and provide details on the amount of irradiance that could be expected. A simplified case that represents a single module deployed under conditions consistent with existing one-sun irradiance standards lead to a bifacial reference condition of 1000 Wcm −2 G front and 130–140 Wcm−2 G rear. For fielded systems of bifacial modules, G rear magnitude and spatial uniformity will be affected by self-shade from adjacent modules, varied ground cover, and ground-clearance height. A standard measurement procedure for bifacial modules is also currently undefined. A proposed international standard is under development, which provides the motivation for this paper. Here, we compare field measurements of bifacial modules under natural illumination with proposed indoor test methods, where irradiance is only applied to one side at a time. The indoor method has multiple advantages, including controlled and repeatable irradiance and thermal environment, along with allowing the use of conventional single-sided flash test equipment. The comparison results are promising, showing that indoor and outdoor methods agree within 1%–2% for multiple rear-irradiance conditions and bifacial module construction. A comparison with single-diode theory also shows good agreement to indoor measurements, within 1%–2% for power and other current–voltage curve parameters.
TL;DR: A new set of performance equations to evaluate the short-circuits current, open-circuit voltage, and maximum power point at any operating conditions is introduced, in excellent agreement with the single-diode PV model, combined with simple and easy application.
Abstract: There are several photovoltaic (PV) performance models in the literature, but most of them either employ complex and tedious calculations or require additional measurements apart from datasheet information. In this paper, a new set of performance equations to evaluate the short-circuit current, open-circuit voltage, and maximum power point at any operating conditions is introduced. The proposed expressions are simple functions of the irradiance and temperature, while they are generally applicable to any crystalline PV module and require only datasheet information as input data. This is achieved by introducing new formulas to determine the irradiance and temperature coefficients that are not provided in the datasheet, thus avoiding empirical constants or additional measurements. The novelty of the performance equations is their solid theoretical background, as they are in excellent agreement with the single-diode PV model, combined with simple and easy application. The proposed PV model is validated and compared with other methods found in the literature through simulations in MATLAB and outdoor measurements on commercial PV modules.
TL;DR: In this article, a decrease of surface passivation quality is observed in FZ, Cz, and mc-Si lifetime samples during light-induced degradation (LID) treatments.
Abstract: A decrease of surface passivation quality is observed in FZ, Cz, and mc-Si lifetime samples during light-induced degradation (LID) treatments. It is shown that this degradation occurs not only in samples with single SiN x :H layers but also when using layer stacks consisting of SiO x /SiN x :H or AlO x :H/SiN x :H. Time-resolved calculation of the surface saturation current density J 0 s is shown to be a reliable method to separate changes in the bulk and at the surface of samples during LID treatments. The impact of the observed changes in passivation quality on the outcome and interpretation of LID experiments aiming at changes in the bulk of Cz or mc-Si is investigated and discussed.
TL;DR: In this article, the effect of the material used for the buffer layer (CdS and ZnS) and the back mirror (Mo, Cu, Au, and Ag) on the short-circuit current of CIGS solar cells was investigated.
Abstract: Novel architectures for light trapping in ultrathin Cu(In,Ga)Se $_2$ (CIGS) solar cells are proposed and numerically investigated. They are composed of a flat CIGS layer with nanostructured back mirrors made of highly reflective metals. Multi-resonant absorption is obtained for two different patterns of nanostructured mirrors. It leads to a dramatic increase in the short-circuit current predicted for solar cells with very thin CIGS layers. We analyze the resonance phenomena and the density of photogenerated carriers in the absorber. We discuss the impact of the material used for the buffer layer (CdS and ZnS) and the back mirror (Mo, Cu, Au, and Ag). We investigate various CIGS thicknesses from 100 to 500 nm, and we compare our numerical results with experimental data taken from the literature. We predict a short-circuit current of $J_{\text{sc}}$ = 33.6 mA/cm $^2$ for a realistic solar cell made of a 200-nm-thick CIGS absorber with a copper nanostructured mirror. It opens a way toward ultrathin CIGS solar cells with potential conversion efficiencies up to 20%.
TL;DR: In this article, the authors proposed a reverse identification method for the parametrization of the single-diode model of photovoltaic cells and modules based on the datasheet values.
Abstract: In the classical parametrization of the single-diode model of photovoltaic (PV) cells and modules based on the datasheet values, first, the values of the five unknown parameters of the PV model are extracted via the values of the open-circuit voltage $V_{{\rm oc}}$ , the short-circuit current $I_{{\rm sc}}$ , and the voltage and current at the maximum power point $V_{m}$ , $I_m$ at standard test conditions (STC) Next, using some translational formulas, the STC values of the unknown parameters are projected to the new climatic conditions other than STC A major problem of this approach is to determine the translational formulas of the five unknown parameters of the single-diode model as a function of both temperature and irradiation levels with a high degree of accuracy beforehand This paper presents a new method to extract the parameters of the PV model that operates with a reverse identification process, as compared with the classical methods, in the sense that it starts with the translational formulas of the key parameters of $V_{{\rm oc}}$ , $I_{\rm{sc}}$ , $V_m$ , and $I_m$ and yields the variation of the all PV model unknown parameters as a function of both temperature and irradiation levels The satisfactory operation of the proposed parametrization technique is evaluated by simulations, experiments, and comparative studies with the classical methods
TL;DR: In this article, the optoelectronic properties and microstructure of molybdenum oxide-based hole contacts are evaluated at different steps of the manufacturing process and shown that the changes in the contact properties result in a barrier that impedes hole transport when measuring I-V characteristics at room temperature.
Abstract: Molybdenum oxide is an efficient hole collector for silicon solar cells. However, its optoelectronic properties deteriorate during cell manufacturing. To assess this issue, the optoelectronic properties and microstructure of molybdenum oxide-based hole contacts are evaluated at different steps of the manufacturing process. Molybdenum oxide becomes more absorbing as it reduces when placed in contact with hydrogenated amorphous silicon, triggering the formation of a 2-nm thick SiO x layer, and when annealed after exposure to the plasma used to sputter the transparent conductive oxide. These changes in the contact properties result in a barrier that impedes hole transport when measuring I–V characteristics at room temperature. Nonetheless, cells still reach an efficiency of up to 20.7% when using a front metal electrode screen-printed at 210 °C (21.7% for reference cells). Above 60 °C, both molybdenum oxide-based and reference cells exhibit the same efficiency as this barrier to hole transport vanishes.
TL;DR: The applicability of some explicit methods for identifying parameter identification in real time and on low-cost, low-performance processing platforms is analyzed for a large class of panels under operating conditions that are different from the standard ones.
Abstract: Recent literature proposes some approaches that employ explicit equations for identifying the five parameters of the single-diode model describing a photovoltaic (PV) panel These methods avoid the iterative solution of a nonlinear system of equations, whose convergence is very sensitive to the guess solution Therefore, they are particularly suitable to perform parameter identification in real time and to be implemented on low-cost, low-performance processing platforms In this paper, the applicability of some explicit methods, previously validated under standard test conditions, is analyzed for a large class of panels under operating conditions that are different from the standard ones The study considers both a consolidated method for translating the PV model parameters as well as a novel approach The analysis allows assessing the most suitable parameter translation equations for each considered explicit identification method, highlighting the effectiveness of such explicit approaches under different operating conditions An in-depth validation based on experimental data concerning two commercial PV panels corroborates the analysis
TL;DR: In this paper, tungsten oxide (WO) was investigated as hole contact on n-type crystalline silicon, and it was found that at least 20nm thick interlayers of WO with the highest possible conductivity were needed to prevent detrimental effects of ITO work function on the band bending at the junction, the implied fill factor (FF) and the real FF of solar cells.
Abstract: Reactively sputtered tungsten oxide ( $\text{WO}_x$ ) was investigated as hole contact on n-type crystalline silicon. Varying the oxygen gas flow during sputtering enables variation of the $\text{WO}_x$ conductivity from 0.01 to 1000 $\Omega$ /cm, while the band bending at the interface and the implied fill factor (FF) change by 70 meV and 1.5%. Sputtered $\text{WO}_x$ shows higher resistivity and higher absorption in the visible range compared with indium–tin–oxide (ITO). Therefore, stacks of $\text{WO}_x$ and ITO are used in solar cells. It was found that at least 20 nm thick $\text{WO}_x$ is needed to prevent detrimental effects of the ITO work function on the band bending at the junction, the implied FF, and the real FF of solar cells. $\text{WO}_x$ hole contacts of different thicknesses and conductivity were applied in solar cells and it was found that the highest FF is achieved using about 20 nm thick interlayers of $\text{WO}_x$ with the highest possible conductivity. It was found that sputtering enables a drastic improvement of $\text{WO}_x$ /silicon solar cells compared with thermal evaporation, due to the precise control of the $\text{WO}_x$ conductivity. Unfortunately, the resistivity of the sputtered $\text{WO}_x$ is still limiting the FF of these devices.
TL;DR: In this article, n-type gallium phosphide on p-type silicon heterojunction solar cells which have been prepared by direct growth via metal-organic vapor phase epitaxy (MOVPE).
Abstract: Gallium phosphide (GaP) is, in theory, a near-ideal heteroemitter for silicon solar cells due to its electronic and crystal properties. In this paper, we present n-type gallium phosphide on p-type silicon heterojunction solar cells which have been prepared by direct growth via metal–organic vapor phase epitaxy (MOVPE). The devices show very promising results in quantum efficiency and current density. However, the open-circuit voltage of 560 mV is far from ideal. The investigation of two different nucleation processes reveals a significant influence of the antiphase domain density at the GaP/Si interface on the open-circuit voltage.
TL;DR: It is shown that the nonconvex optimization problem of PV systems is converted to a convex optimization one and an adaptive identification technique is utilized to find the optimal values of the augmented cost.
Abstract: This paper presents a novel identification technique for estimation of unknown parameters in photovoltaic (PV) systems. A single-diode model is considered for the PV system, which consists of five unknown parameters. Using information about standard test conditions, three unknown parameters are written as functions of the other two parameters in a reduced model. An objective function and a set of inequality constraints are defined for the reduced model, considering limitations of the physical system. It is shown that the nonconvex optimization problem of PV systems is converted to a convex optimization one. The constraints are enforced using a modified barrier function that generates an augmented convex objective function. An adaptive identification technique is utilized to find the optimal values of the augmented cost. Unlike most identification techniques, the proposed algorithm has a precise and unique solution, which is easy to implement. The effectiveness of the proposed approach is confirmed using some simulation and experiments.