Series Resistance Losses Research Articles

Efficiency increase in multijunction monochromatic photovoltaic devices due to luminescent coupling

We present a multijunction detailed-balance model that includes the effects of luminescent coupling, light trapping, and nonradiative recombination, suitable for the treatment of multijunction solar cells and photonic power converters—photovoltaic devices designed to convert the narrow-band light. The model includes both specular and Lambertian reflections using a ray-optic formalism and treats nonradiative processes using an internal radiative efficiency. Using this model, we calculate and optimize the efficiency of multijunction photonic power converters for a range of material qualities and light-trapping schemes. Multijunction devices allow increased voltage with lower current, decreasing series resistance losses. We show that efficiency increases significantly with an increased number of junctions, even without series resistance, when the device has an absorbing substrate. Such an increase does not occur when the device has a back reflector. We explain this effect using a simplified model, which illustrates the origin of the decreased radiative losses in multijunction devices on substrates.

Analytic $I_{\text{sc}}$–$V_{\text{oc}}$ Method and Power Loss Modes From Outdoor Time-Series $I$–$V$ Curves

Utilizing large-scale outdoor $I$ – $V$ data streams, the authors demonstrated a feasible, repeatable method to construct outdoor time-series $I_{\text{sc}}$ – $V_{\text{oc}}$ curves. Resulting Analytic $I_{\text{sc}}$ – $V_{\text{oc}}$ curves are validated with laboratory $Suns$ - $V_{\text{oc}}$ measurements. Comparing $I_{\text{sc}}$ – $V_{\text{oc}}$ with real $I$ – $V$ curves, power loss modes including uniform current loss, recombination loss, series resistance loss, and current mismatch loss can be quantified in units of watts or percent nominal power, making them directly comparable. Above power loss modes are calculated for long-term $I$ – $V$ data from fielded modules in different climate zones, and dominant power loss modes were determined from the resulting time series. This method has been published as an open source package in R programming language.

Design of an indium arsenide cell for near-field thermophotovoltaic devices

An indium arsenide photovoltaic cell with gold front contacts is designed for use in a near-field thermophotovoltaic (NF-TPV) device consisting of millimeter-size surfaces separated by a nanosize vacuum gap. The device operates with a doped silicon radiator maintained at a temperature of 800 K. The architecture of the photovoltaic cell, including the emitter and base thicknesses, the doping level of the base, and the front contact grid parameters, are optimized for maximizing NF-TPV power output. This is accomplished by solving radiation and charge transport in the cell via fluctuational electrodynamics and the minority charge carrier continuity equations, in addition to accounting for the shading losses due to the front contacts and additional series resistance losses introduced by the front contacts and the substrate. The results reveal that these additional loss mechanisms negatively affect NF-TPV performance in a non-negligible manner, and that the maximum power output is a trade-off between shading losses and series resistance losses introduced by the front contacts. For instance, when the cell is optimized for a 1 x 1 mm2 device operating at a vacuum gap of 100 nm, the losses introduced by the front contacts reduce the maximum power output by a factor of ~ 2.5 compared to the idealized case when no front contact grid is present. If the optimized grid for the 1 x 1 mm2 device is scaled up for a 5 x 5 mm2 device, the maximum power output is only increased by a factor of ~ 1.08 with respect to the 1 x 1 mm2 case despite an increase of the surface area by a factor of 25. This work demonstrates that the photovoltaic cell in a NF-TPV device must be designed not only for a specific radiator temperature, but also for specific gap thickness and device surface area.

Development of High‐Efficiency n‐Type Front and Back Contact Passivated Emitter and Rear Locally Diffused Solar Cells Using Atmospheric Pressure Chemical Vapor Deposition of Phosphosilicate Glass and Laser Processing

Industrial bifacial n‐type front and back contact (nFAB) silicon solar cells, consisting of a boron‐doped p+ emitter and a phosphorus‐doped n+ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus‐doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (Rs) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open‐circuit voltage (Voc) of 662 mV, short‐circuit current density (Jsc) of 39.6 mA cm−2, and a high FF of 81.1%.

Numerical optimisation and recombination effects on the vertical-tunnel-junction (VTJ) GaAs solar cell up to 10,000 suns

Ultra-high concentrator photovoltaic systems (UHCPV), usually referred to CPV systems exceeding 1000 suns, are signalled as one of the most promising research avenues to produce a new generation of high-efficiency and low-cost CPV systems. However, the structure of current concentrator solar cells prevents their development due to the unavoidable series resistance losses at such elevated concentration ratios. In this work, we investigate the performance of the so-called vertical-tunnel-junction (VTJ), recently introduced by the authors, by using advance TCAD. In particular, we carry out an optimisation procedure of the key parameters that affect its performance and conduct a deep investigation of the impact of the main recombination mechanisms and of sun concentration up to 10,000 suns. The results indicate that the performance of the novel structure is not significantly affected by these two factors. A record efficiency of 32.2% at 10,000 suns has been found. This represents a promising way to obtain state-of-the-art efficiencies above 30% for single-band-gap cells, and offers a new route towards the development of competitive CPV systems operating at ultra-high concentration fluxes.

Cost‐effective energy harvesting at ultra‐high concentration with duplicated concentrated photovoltaic solar cells

AbstractConcentrated photovoltaic (CPV) systems are one of the few technologies that can provide cost reduction while offering efficiency improvement. In this respect, the resistive losses are some of the main limiting factors, which restrict the efficiency improvement and the cost reduction at ultrahigh concentrations (UHCs). In this work, we propose and investigate new designs consisting of duplicated junction solar cells. The approach can resolve the issues related to the resistive losses. Simulation results, based on Shockley‐Queisser limit, demonstrate that the detrimental effects of series resistance losses in the degradation of efficiency at UHC factor can be mitigated with this strategy. The modeled structures are composed of multiple junctions of materials (GaInP, GaAs, and Ge), which are lattice‐matched to Ge or GaAs. These results illustrate the potential of duplicated junction designs for enhancing efficiency of III‐V solar cells under high concentrations, exceeding 1000 suns (under AM1.5D solar spectrum at 300 K). Finally, a relative cost calculation indicates that more than 30% of cost reduction can be achieved using these designs at UHCs.

Tracking-free adaptive contact concentration photovoltaics

Adaptive Contact Concentration Photovoltaics (ACCPV) is outlined as a scheme to access CPV efficiency improvements without mechanical tracking. This could allow CPV to play a role in applications where maintenance-free reliability and compact size are essential requirements. Conversion efficiency enhancement using sunlight concentration in multi-junction or potentially single junction solar cells due to the well-known increase in the Shockley-Quessar limit are enabled by replacing a tracking system with an array of switchable electrodes. Cell electrodes are segmented and are connected employing a switching system that adapts to sunlight conditions. Unlike CPV systems, the ACCPV concept allows for effective operation in diffuse sunlight conditions. System losses that must be considered in order to determine whether a net benefit for ACCPV exists for a given solar cell type include optical losses, series resistance losses, and Auger losses. The ACCPV concept is clearly presented and relevant system losses are discussed. A 3% absolute increase in triple junction cell efficiency is projected.

Low-Temperature $p$-Type Microcrystalline Silicon as Carrier Selective Contact for Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells have reached record efficiency, particularly in all-back contacted architectures. Despite this, two-side contacted SHJ cells still suffer from parasitic absorption and series resistance losses in the amorphous silicon contacts. An alternative to the doped amorphous silicon layer is microcrystalline silicon, which exhibits improved transparency and charge transport, while maintaining the superior passivation quality of all-silicon contact stacks. However, depositing thin, highly crystalline films has remained a challenge until recently. In this work, we use deposition temperatures $p$ -type $\mu$ c-Si:H contact layers. With these layers, we demonstrate $J_{\text{sc}}$ gains of 1 mA/cm $^2$ , while reducing series resistance below 1 $\Omega$ cm $^2$ , leading to screen printed 4 cm $^2$ cells with certified $\eta =\text{23.45}\%$ . Using a suite of device and material characterization techniques, we show that reduced deposition temperature leads to an increase in crystalline volume fraction from 35% to 55% for $p$ -type films, which mitigates parasitic absorption in the front contact and facilitates hole extraction. These improvements are explained as resulting from higher transparency in the $p$ -type layer accompanied by higher band bending in the c-Si wafer. These findings provide a method to improve SHJ solar cells performance, while offering insight into the importance of band bending considerations when optimizing heterojunction designs.

Optical design and experiment evaluation of a novel asymmetric compound parabolic concentrator (ACPC) integration with PV for building south wall application

Compound parabolic concentrator (CPC) as a typical low-concentration-ratio concentrator is an interesting topic for it can work as the static concentrator without any additional tracking systems or seasonal adjustments, which shows a promising concept of introducing the concentrating PV technology for building application. Therefore, based on the compound parabolic curves, a novel asymmetric compound parabolic concentrator (ACPC) is proposed in this paper for building south wall integration. The optical model of the ACPC is built by the software Lighttools to study its optical performance, and the structure parameters of it are optimized through the optical simulation. Then the prototype of the ACPC integrated with the PV cell as the ACpC-PV module is manufactured and assembled. The indoor experiments by the solar simulator (Oriel Sol3A Model 90943A) from the Newport Corporation at the dark environment with the temperature of 25 °C are conducted to study the electrical performance of the ACPC-PV module. The simulation and experiment results show that the acceptance range of the ACPC with the geometric concentration ratio of 2.4X can be 65° with high optical efficiency. A good agreement is observed between the simulation and experiment results despite the deviation of around 13% which is inevitable due to all kinds of errors, such as manufacturing errors, mismatch losses, series resistance losses, etc.

A fault diagnosis method for photovoltaic arrays based on fault parameters identification

Aiming at evaluating the state of the photovoltaic (PV) array and improving the reliability of the PV system, a fault diagnosis method for PV arrays based on fault parameters identification is proposed in this paper. Compared with existing fault diagnosis methods, the proposed method has advantages of recognizing concurrent faults and describing each fault quantitatively by identifying fault parameters from the measured current-voltage (I–V) curve of the PV array. The methodology consists of three parts. Firstly, functional relationships between unknown parameters in the one-diode model of PV cells with environmental parameters are obtained by parameters extraction. Secondly, a code-based fast fault simulation model (CFFSM) is established to simulate I–V curves of the PV array under various faulted conditions. Thirdly, by determining the fault parameters to be identified and constructing an objective function that is the error between the simulated I–V curve with the measured I–V curve, an optimization problem is formulated, in which optimal fault parameters are identified by applying the differential evolution (DE) algorithm. The validation experiments in summer and early spring show that the proposed diagnosis method can identify the parameters of up to three concurrent faults, including partial shading, short circuit, and increased series-resistance losses, under good irradiance condition with high accuracy.

Application of compound parabolic concentrators to solar photovoltaic conversion: A comprehensive review

The use of concentrating systems has been proposed as a way to reduce the cost of electrical energy from photovoltaic (PV) module. Since 1970s, different solar collector designs have been used to increase energy flux on the PV module. This study aims at providing a comprehensive review of development in the application of compound parabolic concentrators (CPCs) to solar photovoltaic conversion for the past five decades. By narrowing down the application of CPCs to electrical energy only gives a reader an opportunity to clearly understand the detail development stages, challenges, and research opportunities for further improvement. From this review, it has been found that during 1970s, all studies on the application of CPCs to solar photovoltaic conversion were mainly focused on establishing technical feasibility and cost effectiveness. Thereafter (1981-May 2018), extensive studies were carried out to resolve challenges that were observed during the establishment stage. However, it has been found that even though the power output of the PV modules with the CPC was always higher than similar modules without the CPC, the values were less than the expected (theoretical) results. This was due to optical losses, series resistance losses, non-uniform illumination effect, and high operating cell temperature effect. In addition, high cost of the PV-CPC systems and low concentration ratio of the CPCs were also the main concerns of various researchers.

Fabrication of a Silicon Nanowire Solar Cell on a Silicon-on-Insulator Substrate

This study proposes metal-assisted chemical etching (MAE) as a facile method to fabricate silicon nanowire (SiNW) array structures, with high optical confinement for thin crystalline silicon solar cells. Conventional SiNW arrays are generally fabricated on Si wafer substrates. However, tests on conventional SiNW-based solar cells cannot determine whether the photo-current is derived from SiNWs or from the Si wafer. Herein, SiNW arrays were fabricated on a silicon-on-insulator substrate with a 10-μm-thick silicon layer for measuring the photocurrent of the SiNW only. The 9 μm-long p-type SiNW arrays were applied to a solar cell structure fabricated using an n-type H-doped amorphous Si layer, thereby confirming the photovoltaic effect. However, the device exhibited a conversion efficiency of 0.0017% because of a low short-circuit current (Jsc) and a low open-circuit voltage (Voc). The low Jsc resulted from a high series resistance and high absorption loss from the amorphous Si layer, whereas the low Voc resulted from the high surface recombination velocity of the SiNW array structure. Therefore, reducing the surface recombination of SiNW-based solar cells can improve their conversion efficiency.

Micron-sized liquid nitrogen-cooled indium antimonide photovoltaic cell for near-field thermophotovoltaics.

Simulations of near-field thermophotovoltaic devices predict promising performance, but experimental observations remain challenging. Having the lowest bandgap among III-V semiconductors, indium antimonide (InSb) is an attractive choice for the photovoltaic cell, provided it is cooled to a low temperature, typically around 77 K. Here, by taking into account fabrication and operating constraints, radiation transfer and low-injection charge transport simulations are made to find the optimum architecture for the photovoltaic cell. Appropriate optical and electrical properties of indium antimonide are used. In particular, impact of the Moss-Burstein effects on the interband absorption coefficient of n-type degenerate layers, and of parasitic sub-bandgap absorption by the free carriers and phonons are accounted for. Micron-sized cells are required to minimize the huge issue of the lateral series resistance losses. The proposed methodology is presumably relevant for making realistic designs of near-field thermophotovoltaic devices based on low-bandgap III-V semiconductors.

26.1%‐efficient POLO‐IBC cells: Quantification of electrical and optical loss mechanisms

AbstractWe present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly‐Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p‐type FZ wafer and 24.6% on a 2 Ω cm n‐type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current‐voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly‐Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process‐induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).

Sulfur-hyperdoped silicon nanocrystalline layer prepared on polycrystalline silicon solar cell substrate by thin film deposition and nanosecond-pulsed laser irradiation

Silicon (Si)-based solar cells are the main products in current photovoltaics market; therefore, any development in their conversion efficiency and cost effectiveness provides an extremely important contribution to the photovoltaic industry. Use of hyperdoping process for the achievement of Si sub-bandgap light absorption to improve conversion efficiency has attracted significant attention of researchers. However, several problems are encountered during this process such as the poor crystallinity, severe carrier recombination, and high series resistance loss. In this study, a sulfur (S)-hyperdoped Si nanocrystalline layer is prepared on a commercial polycrystalline Si solar cell substrate to efficiently utilize near-infrared (NIR) and visible lights, respectively. An inexpensive, rectangle shaped nanosecond-pulsed laser beam is used to rapidly irradiate SiSSi multilayered films to produce this hyperdoped layer via melting, vaporization, resolidification, and crystallization processes. The hyperdoped samples which have S impurity concentration in the range of 0.15 ± 0.07–0.78 ± 0.03 at.%, exhibit high NIR light absorptance (75–90%), high bulk carrier concentration (≥1019 electrons·cm−3) and mobility (∼102 cm2 V−1 s−1), and low sheet resistance (<100 Ω·square−1) and resistivity (∼10−3 Ω cm). The results confirm that this method not only improves the laser processing efficiency and saves costs, but also realizes a stable liquid S-hyperdoping process to prepare a nanocrystalline layer with strong IR properties.

Condition monitoring of aluminium electrolytic capacitors using accelerated life testing

PurposeAn electrolytic capacitor is extensively used as filtering devices in various power supplies and audio amplifiers. Low cost and higher value of capacitance make it more well known. As environmental stress and electrical parameters increase, capacitors degrade on accelerated pace. The paper aims to discuss these issues.Design/methodology/approachThis paper focusses on the impact of thermal stress on electrolytic capacitors using accelerated life testing technique. The failure time was calculated based on the change in capacitance, equivalent series resistance and weight loss. The experimental results are compared with the outcome of already available life monitoring methods, and the accuracy level of these methods is accessed.FindingsThe results of all the three methods are having maximum 55 per cent accuracy. To enhance the accuracy level of theoretical methods, modifications have been suggested. A new method has been proposed, whose outcome is 92 per cent accurate with respect to experimentally obtained outcomes.Practical implicationsTo assess the capacitor’s reliability using an experimental and modified theoretical method, failure prediction can be done before it actually fails.Originality/valueA new method has been proposed to access the lifetime of capacitor.

Study of a New Structural Photovoltaic Module

The parallel arrangement of cells could reduce the current level in each string and hence decrease the series resistance loss and increase the module output power. The morphology of the cross-sections of separated cells by nondestructive cutting or infrared nanosecond laser cutting tech was comparatively characterized in this study. The obtained results demonstrate that the cross-section by non-destructive cutting tech was smooth and no nanocrack was found, which could benefit the module output power during the entire operating lifetime. Also, soft welding ribbons were employed in our study to replace the common conducting paste for the interconnection of separated cells. Modules assembled with this non-destructive cut cells can fully endure the simulated environmental tests.

Impact of the Presence of Busbars During the Fast Firing Process on Contact Resistances

Uniform and low contact resistances between Ag grids and Si emitters are very important for reducing series resistance losses in screen-printed silicon solar cells. In this paper, we studied systematically the contact resistance of firing-through Ag pastes on samples that were processed in a fast firing furnace with and without the presence of busbars. We fabricated p-type full-area aluminum back surface field and n-type passivated emitter rear totally diffused solar cells with various doping concentrations and surface morphologies. For all tested conditions, lower contact resistances were obtained when firing without busbars. For instance, by omitting the busbars during firing, on a 138 $\Omega$ /sq phosphorus emitter, the median contact resistance dropped from 7.5 to 0.7 m $\Omega$ $\cdot$ cm $^{2}$ , and on an 85 $\Omega$ /sq boron emitter, the median contact resistance decreased from 80 to 1 m $\Omega$ $\cdot$ cm $^{2}$ . Furthermore, we found that the pure Ag paste outperformed the AgAl paste in contacting boron emitters. An explanation of these results might be the short-circuit effect, which is a fundamental mechanism that strongly influences contact formation. In addition, in spite of the significant impact of the presence of busbars during firing on contact resistances, its impact on the $J_{0,\text{met}}$ was found to be only marginal.

Monocrystalline 1.7-eV-Bandgap MgCdTe Solar Cell With 11.2% Efficiency

This work demonstrates a monocrystalline 1.7 eV Mg0.13Cd0.87Te solar cell with an open-circuit voltage of 1.176 V and an active-area efficiency of 11.2%. The absorber layer is clad in wider bandgap passivation layers that effectively confine electrons and holes via the resulting band offsets. The potential barriers cladding the absorber are generated using higher magnesium compositions than the absorber and provide excellent carrier confinement. This ultimately leads to long minority carrier lifetimes (>500 ns) and high photoluminescence quantum efficiencies yielding an implied open-circuit voltage of 1.3 V. However, the same barriers at the heterointerfaces reduce fill factor by impeding transport; this is apparent as series resistance losses that can be overcome with operation at higher temperatures. The photocurrent loss mechanisms are simulated and analyzed, laying out the pathway for further improvements in current generation and, thus, efficiency.

Estimation of transmission loss components from phasor measurements

This paper presents a method to estimate separate components of transmission losses from synchronised phasor measurements in terms of losses in the corresponding elements of the transmission line model. This means separate estimates of Joule losses in series resistive elements and active losses dissipated in the shunt conductive elements, e.g. corona and leakage, and both the consumed and generated reactive power in inductive and capacitive elements of the model are found. The main aim and benefit of the method is a new way to detect corona losses on transmission lines. To facilitate this, the needed mathematical expressions are derived for the estimation of transmission losses from simultaneous, i.e. time-synchronised, phasor measurements based on a distributed parameter multiconductor transmission line model. The efficacy of the derived expressions is analysed in PSCAD simulations and on real data from phasor measurement units (PMU).