Series Resistance Losses Research Articles

A new path towards ultra-high efficient laser power converters: Silicon carbide-based multijunction devices

Current high power laser transmission technology faces two major limitations to improve the efficiency of the photovoltaic receivers: the intrinsic entropic losses associated to low bandgap materials (such as GaAs) and the series resistance losses that degrade the device performance at high power densities. The use of high bandgap materials and new architectures for laser power converters (LPC) have been pointed out as alternatives to overcome these limitations. In this work, three silicon carbide polytypes (3C, 4H and 6H) are proposed as base materials for the standard horizontal laser power converter (hLPC) architecture and the Vertical Epitaxial Hetero-Structure Architecture (VEHSA). 3C SiC based hLPCs outperform the power converters based on the other two polytypes, achieving a maximum efficiency of 84.6% at ▪, but suffer from series resistance losses, that deteriorate their efficiency, at higher laser power densities. This issue is solved with 3C SiC 4 cells VEHSAs that demonstrated increasing efficiency with the input power, reaching a maximum of 87.4% at ▪. The VEHSA reduced number of cells minimize the risks of efficiency losses due to current mismatch between cells. These results support the feasibility of a new generation of LPCs capable of efficiently convert ultra-high laser power densities.

21.2% GaAs Solar Cell Using Bilayer Electron Selective Contact

GaAs remains one of the crucial materials for solar cell applications as it boasts the world's highest efficiency single‐junction solar cells. However, their high cost limits their widespread terrestrial applications. Traditional GaAs solar cells require a complex stack of doped junctions, which can only be grown using epitaxy, which is a very costly technique. Herein, a nonepitaxial bilayer of ZnO and TiO2 as electron‐selective contact is studied. It is shown that a bilayer selective contact can achieve very high performance through interface band engineering and a reduction of the barrier for electron transfer. 21.2% efficient solar cells is achieved, with Voc of 1.04 V, Jsc of 26.13 mA cm−2, and a fill factor of 77.8%. The Voc reported in the article is comparable to the highest Voc reported for substrate‐based GaAs solar cells of 1.075 V. An experimental loss analysis shows that the device is mainly limited by series and shunt resistance and reflection losses, both of which can further be minimized by optimization of the fabrication process. The results presented will be very useful for the further development of cheaper GaAs solar cells, whereas the bilayer selective contact concept can be implemented for other kinds of solar cells.

Understanding the Interfacial Reactions and Band Alignment for Efficient and Stable Perovskite Solar Cells Built on Metal Substrates with Reduced Upscaling Losses.

Conventional perovskite solar cells (PSC) built on transparent conductive oxide (TCO) glass face a fundamental challenge to retain fill factor (FF) for large-area upscaling due to series resistance loss. Building a perovskite solar cell on metal has the potential to reduce this FF loss and is promising for flexible applications. However, their efficiency and stability lag far behind their TCO counterparts. Herein, findings on the complex chemical reactions and degradation-promoting processes at different perovskite/metal (Cu, Au, Ag, and Mo) interfaces, which are closely linked with the inherent stability; and the interlayer engineering for perovskite/metal interface's band alignment, which plays an essential role in achieving high efficiency, are reported. Leveraging these findings, 21% power conversion efficiency (PCE) is achieved for 1 cm2 perovskite solar cells using a p-i-n top-illumination structure on a molybdenum substrate, the highest reported for a PSC built on metal. Notably, the FF and PCE losses due to area upscaling are remarkably reduced by one order of magnitude relative to the counterparts on conventional TCO glass, highlighting an alternative pathway for PSC upscaling and module design.

Self-Operating Flyback Converter for Boosting Ultra-Low Voltage of Thermoelectric Power Generator for IoT Applications

This article presents a novel self-operating flyback converter to boost the ultra-low voltage produced by thermoelectric power generator (TEG). The proposed converter uses dual transformer, one for low-voltage startup and other to extract power from TEG. The use of separate transformer provides high-voltage transfer ratio, reduces high series resistance loss, and brings down the input impedance of circuit. The copper wire wounds ferrite toroid core transformer provides very low series resistance and negligible core loss, which improves the circuit efficiency. This boost converter operates with an input voltage range of 22–300 mV and provides maximum output power of 0.073 – 147 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{mW}}$</tex-math></inline-formula> correspondingly. The peak efficiency of 68% with output power of 1.32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{mW}}$</tex-math></inline-formula> (voltage ∼1.83 V) is achieved at an input voltage of 50 mV. For regulated output voltage, a feedback loop is used to keep output voltage constant during sudden voltage rise of TEG. The proposed circuit uses discrete components, ferrite toroid core, and PCB, which has lower cost than available energy harvester module, which uses energy harvesting ICs, discrete components, and tiny transformer. The lower startup voltage, higher output power, and voltage with high conversion efficiency of this boost converter maximize the applications potential of the TEG as a portable power source for Internet of Things (IoT) devices.

Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p+ Contacts in the Constraints of Measurement and Module Integration

Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide emitter and an aluminum‐doped p+ base contact on M2‐sized Ga‐doped p‐type Cz wafers are reported. The Al‐doped base contact forms during the firing of the printed contacts and allows for a lean process flow. The device optimization balances recombination at the base contacts against resistive losses and respects constraints set by the need of interconnecting cells in a module and contacting the cells temporally by a measurement chuck. A special sample holder is designed for measuring the Isc–Voc curve of the IBC cell with a busbar‐less metal grid. The pseudo‐efficiency is 24.7%. All fingers of each polarity are connected with wires and an efficiency of 22.3% is measured. The comparison of simulations and measurements reveals that the cell has 23.4% efficiency without the series resistance losses due to the wires. A huge part of the resistive losses in the cell are the transport losses of the majorities in the base dissipating a power that corresponds to 0.76%abs efficiency and the resistive losses at the Al‐doped base contact (0.29%abs).

Progress with screen printed metallization of silicon solar cells - Towards 20 μm line width and 20 mg silver laydown for PERC front side contacts

Within this work, we evaluate and compare different high-end screens for the fine line front side metallization of passivated emitter and rear cell (PERC) solar cells. Three types of high-end screens are considered including (i) a fine mesh screen configuration with a mesh count MC = 520 wires/inch and standard mesh angle of φ = 22.5°, (ii) a knotless screen configuration with a mesh angle of φ = 0° as well as (iii) a knotless screen configuration utilizing a rectangular mesh with different mesh count in warp and weft direction MC = 460/430 wires/inch. Using these advanced screen configurations, all PERC solar cells are metallized with a busbarless fine line front side grid at a nominal contact finger opening of 20 μm and 24 μm. All screen configurations obtained excellent results regarding finger geometry, silver laydown and electrical performance of the front side grid and the fabricated PERC solar cells. The most efficient group obtained a printed mean finger width of 21 μm with a silver laydown of only 19 mg and revealed a mean energy conversion efficiency of 22.7%. Furthermore, we investigate the geometric and electric results of the printed front side contacts in detail using advanced image analysis software and scanning electron microscopy and discuss the impact of the fine line front side metallization on the applicable cell interconnection concepts depending on the series resistance losses. • Evaluation of different high-precision screen configurations for fine line metallization of PERC solar cells. • Reduction of silver laydown to less than 20 mg on the front side while maintaining excellent I–V-results of the solar cells. • In-depth analysis of the geometric properties and electric results of the printed fine line front side contacts. • Discussion of the impact of different screen configurations on various aspects of solar cells.

Interdigitated back-contacted crystalline silicon solar cells fully manufactured with atomic layer deposited selective contacts

The interdigitated back-contacted (IBC) solar cell concept has been extensively studied for single-junction cells and more recently as a good choice for three-terminal tandem devices. In this work, carrier-selective contacts based on transition metal oxides deposited by atomic layer deposition (ALD) technique are applied to IBC c-Si(n) devices. In the first part of the study, we develop a hole-selective contact based on thin ALD vanadium oxide (V2O5) layers without using an amorphous silicon interlayer. The ALD process has been optimised, i.e. number of ALD cycles and deposition temperature, as a trade-off between surface passivation and contact resistivity. Noticeable surface passivation with recombination current densities around 100 fA/cm2, as well as reasonable contact resistivity values below 250 mΩcm2 are reached using 200 ALD V2O5 cycles deposited at a deposition temperature of 125 °C (∼10 nm layer thickness). The optimised ALD V2O5-based contact is combined with both an ALD TiO2-based electron-selective contact and an excellent surface passivation in non-contacted regions provided by ALD Al2O3 films, to form a fully ALD IBC c-Si(n) solar cell scheme. Fabricated devices yield photovoltaic efficiencies and pseudo efficiencies, i.e. calculated without series resistance losses, of 18.6% and 21.1% respectively (3 cm × 3 cm device area). These results reveal the potential of the ALD technique to deposit transition metal oxide (TMO) films as selective contacts on high efficiency devices, paving the way of using low thermal-budget, low cost and highly scalable processes for a highly demanding IBC solar cell architecture in the photovoltaic industry.

Fully integrated switched‐inductor switched‐capacitor dual‐path DC–DC converter

SummaryA fully integrated switched‐inductor switched‐capacitor (SISC) DC–DC converter is proposed. This converter is designed in such a way that the input voltage can be twice the process allowable voltage without damaging the on‐chip transistors. To mitigate large series resistance of on‐chip inductors as one of the main challenges in the switched‐inductor power supply on chip, two solutions are proposed. By using analytical model of an on‐chip inductor, optimal physical dimensions are designed to achieve the desired inductance with minimum series resistance in a small area. Along with the optimization, the dual‐path structure of the proposed converter reduces series resistance losses of the on‐chip inductor and increases the effective quality factor up to 7 times in duty cycle of 0.8. The proposed converter is implemented in 0.18 μm standard CMOS process. The circuit converts input voltage of 3.6–0.9 V at the load current of 125 mA with the efficiency of 72.8%. Efficiency enhancement factor reaches 72% at 600 mV output voltage. The achieved current density of the proposed converter is 333 mA/mm2. By calculating small signal model of the proposed converter and designing a suitable feedback loop, an appropriate transient behavior was proved

Fill Factor Assessment in Hole Selective Layer Free Carbon Electrode‐Based Perovskite Solar Cells with 15.5% Certified Power Conversion Efficiency

Carbon‐electrode‐based perovskite solar cells (C‐PSCs) are promising candidates for commercialization due to their high stability. However, the absence of a hole selective layer (HSL) often limits their performance, yielding low fill factors (FFs). Herein, a certified FF of 78.8% obtained through HSL‐free C‐PSCs is focused. This is found to approach the highest values reported for metal‐electrode‐based PSCs employing highly selective HSLs. The loss mechanisms affecting the FF in fully printed HSL‐free C‐PSCs are thus investigated. Methods commonly used to analyze and quantify the impact of recombination and transport losses on the FF of established photovoltage devices are assessed, and their applicability in C‐PSCs is examined. In the improved devices, non‐radiative recombination contributes to only 3%abs loss with respect to the FF in the radiative limit, which is attributed to an optimal diode ideality factor approaching 1.0. Moreover, contributions of shunt resistive losses are determined to be negligible. Interfacial series resistance losses at the perovskite/carbon interface are identified as the main loss channel, highlighting the importance of the quality of the contact between the perovskite and the back‐contact electrode.

Initial Approaches for Developing Low-Cost Materials for PEM Water Electrolyzer Porous Transport Layers

Capital cost is a major barrier to the widespread commercialization of water electrolysis technology. Metal-based stack components, particularly the porous transport layers (PTLs) and bipolar plates (BPPs), are estimated to represent 30-70% of electrolyzer stack cost [1]. Current commercial approaches utilize titanium, which forms a passive oxide film that provides corrosion resistance in the electrolyzer anode environment. During operation, however, the electrically resistive surface oxide film grows, which leads to significant increases in cell and stack series resistance losses. Successful mitigation strategies so far have relied on a platinum-group metal (PGM) coating. With titanium alloy base materials and PGM coatings being relatively expensive, there is significant potential to reduce electrolyzer stack cost by using alternative materials.In the more advanced trajectory of fuel cell research and development, there has been considerable exploration and validation of a variety of base materials and surface modifications [2]. The primary materials have been metals or carbon-based (e.g. graphite bipolar plates or carbon paper diffusion media). Although potentially suitable in the electrolyzer cathode environment, carbon is not stable under the highly oxidizing and acidic environment of an electrolyzer anode. Therefore, metal alloys that form passive oxides are necessary, but such passive oxides generally have high electrical resistance. This defines the primary design challenge for engineering new PTL materials.In efforts toward selecting, screening, and developing promising, low-cost PTL materials, we have explored and developed ex-situ characterization techniques to be used in concert with in-situ PTL performance validation. Ex-situ measurements include interfacial contact resistance, electrochemical corrosion current, permeability, and insulating oxide formation. One facet of ex-situ corrosion testing methodology involves individually varying stressors such as temperature, pH, and potential to quantify the influence of each. Another facet employs time-lapse microscopy to observe and interpret distinct corrosion modes. These approaches will be discussed and example results for baseline and low-cost PTL materials and surface modifications will be presented.

Scalable semitransparent prototype organic photovoltaic module with minimal resistance loss

Semi-transparent organic photovoltaic (ST-OPV) cells are regarded as an attractive solution to building-integrated solar energy harvesting. Both the power conversion efficiency ( PCE ) and average photopic transmission ( APT ) of ST-OPVs have shown substantial increases in recent years. However, less attention has been paid to the area scaling of ST-OPV cells. In this work, we investigate the scalability of ST-OPV cells from 4 mm 2 to 1 cm 2 , as well as 9 cm 2 active area prototype module. By integrating both top and bottom metal grids onto the transparent electrodes, the series resistance loss of 1 cm 2 ST-OPV cell is significantly reduced, and is comparable to that of the grid-free 4 mm 2 cell. Nine 1 cm 2 cells are then connected in a series-parallel circuit to realize a prototype ST-OPV module. A 100% fabrication yield with only 5% PCE deviation among discrete cells is achieved. The semitransparent module shows PCE = 7.2 ± 0.1% under simulated AM 1.5G illumination at 1 sun intensity, which exhibits no connection resistance loss compared to that of the individual cells. The ST-OPV module exhibits an APT = 38.1 ± 1.1%, which enables a light utilization efficiency, LUE = 2.74 ± 0.09%. The method demonstrates a promising way for ST-OPV modules to scale without compromising performance. • Semitransparent organic photovoltaic cells are scaled from 4 mm 2 to 1 cm 2 employing metal grids without loss of performance. • The 9 cm 2 active area prototype modules have 100% cell yield and with performance comparable to that of 4 mm 2 cells. • The module shows PCE = 7.2%, an average photopic transparency of 38.1%, enabling a light utilization efficiency of 2.74%. • The method demonstrates a promising path for scaling to modules without compromising performance.

Comparison of highly conductive natural and synthetic graphites for electrodes in perovskite solar cells

In this work we compare seven different types of natural and synthetic graphite particles and examine how their integration into the cathode of carbon-based perovskite solar cells (C–PSCs) is influencing their opto-electronic properties. By combining x-ray diffraction, Raman spectroscopy and 4-point probe measurements we show that the differences in graphite crystallinity significantly affect the sheet resistance of the carbon-based cathode. The most conductive carbon-based film with an exceptional sheet resistance of 4 Ω/sq. have been produced from scaly graphite with the crystallite dimensions of La = 60.6 nm and Lc = 28.6 nm. Electrochemical Impedance Spectroscopy further revealed that charge transfer resistance at the perovskite/carbon contact differ for each graphite type. Overall, the pyrolytic graphite was found to be the best compromise between high conductivity and low charge transfer resistance leading to least series resistance losses and a fill factor (FF) above 74% (in perovskite solar cells with area of 0.64 cm2). However, an overall efficient hole extraction and lower non-radiative charge recombination in C–PSCs with scaly graphite resulted in the highest average power conversion efficiency and a champion device reaching 14.63%. All the C–PSCs show exceptional moisture stability for 5,000 h under ambient condition, with a PCE decrease of less than 3%.

Loss mechanism analyses of perovskite solar cells with equivalent circuit model

Perovskite solar cells have been attracting more and more attentions due to their extraordinary performances in the photovoltaic field. In view of the highest certified power conversion efficiency of 25.5% that is much lower than the corresponding Shockley-Queisser limit, understanding and quantifying the main loss factors affecting the power conversion efficiency of perovskite solar cells are urgently needed. At present, the three loss mechanisms generally recognized are optical loss, ohmic loss, and non-radiative recombination loss. Including the trap-assisted bulk recombination and surface recombination, the non-radiative recombination is proved to be the dominant recombination mechanism prohibiting the increase of efficiency. In this work, based on semiconductor physics, the expressions of bulk and surface recombination currents are analytically derived. Then taking the optical loss, series and shunt resistance losses, and bulk and surface recombination losses into considerations, an equivalent circuit model is proposed to describe the current density-voltage characteristics of practical perovskite solar cells. Furthermore, by comparing to the drift-diffusion model, the pre-defined physical parameters of the drift-diffusion model well agree with the fitting parameters retrieved by the equivalent circuit model, which verifies the reliability of the proposed model. For example, the carrier lifetimes in the drift-diffusion model are consistent with the recombination factors in the equivalent circuit model. Moreover, when the circuit model is applied to analyze experimental results, the fitting outcomes show favorable consistency to the physical investigations offered by the experiments. And the relative fitting errors of the above cases are all less than 2%. Through employing the model, the dominant recombination type is clearly identified and split current density-voltage curves characterizing different loss mechanisms are offered, which intuitively reveals the physical principles of efficiency loss. Additionally, through calculating the efficiency loss ratios under the open-circuit voltage condition, quantifying the above-mentioned loss mechanisms becomes simple and compelling. The prediction capability of the model is expected to be enhanced if a series of light intensity dependent current density-voltage curves are fitted simultaneously. Consequently, this model offers a guideline to approach the efficiency limit from a circuit-level perspective. And the model is a comprehensive simulation and analysis tool for understanding the device physics of perovskite solar cells.

In-Situ Measurement of Power Loss for Crystalline Silicon Modules Undergoing Thermal Cycling and Mechanical Loading Stress Testing

An in-situ method is proposed for monitoring and estimating the power degradation of mc-Si photovoltaic (PV) modules undergoing thermo-mechanical degradation tests that primarily manifest through cell cracking, such as mechanical load tests, thermal cycling and humidity freeze tests. The method is based on in-situ measurement of the module’s dark current-voltage (I-V) characteristic curve during the stress test, as well as initial and final module flash testing on a Sun simulator. The method uses superposition of the dark I-V curve with final flash test module short-circuit current to account for shunt and junction recombination losses, as well as series resistance estimation from the in-situ measured dark I-Vs and final flash test measurements. The method is developed based on mc-Si standard modules undergoing several stages of thermo-mechanical stress testing and degradation, for which we investigate the impact of the degradation on the modules light I-V curve parameters, and equivalent solar cell model parameters. Experimental validation of the method on the modules tested shows good agreement between the in-situ estimated power degradation and the flash test measured power loss of the modules, of up to 4.31 % error (RMSE), as the modules experience primarily junction defect recombination and increased series resistance losses. However, the application of the method will be limited for modules experiencing extensive photo-current degradation or delamination, which are not well reflected in the dark I-V characteristic of the PV module.

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

Summary In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.

(Keynote) High Efficiency Heterojunction c-Si Based Solar Cell and Module

1. INTRODUCTION High-efficiency heterojunction (HJ) back-contact crystalline Si (c-Si) solar cells with record-breaking conversion efficiencies are reported. We have so far focused our attention on the HJ technology using amorphous Si (a-Si) passivation layers, and we reported the fabrication of a large-area both-side-contact HJ c-Si solar cell with a record-breaking cell conversion efficiency of 25.1% in 2015 [1]. Using our HJ technology, we have achieved a record-breaking cell conversion efficiency of 26.7%, and a module conversion efficiency of 24.5% in c-Si solar cells [2]. Recent improvements of perovskite solar cells and c-Si solar cells have opened a path to realizing conversion efficiencies of over 30% by using a tandem structure solar cell. Recently, a 29.15%-efficiency perovskite-silicon tandem solar cell was reported [3]. In this paper, we report our state-of-the-art technologies for high-efficiency HJ c-Si solar cells and present perspectives for further improvement of conversion efficiency using tandem solar cells with high-efficiency HJ c-Si and perovskite solar cells based on our recent results. 2. HJBC solar cell Heterojunction back-contact c-Si solar cells (HJBC solar cells) are fabricated using n-type CZ crystalline Si wafers. Figure 1 shows appearance and a typical schematic image of a cross section and of the HJBC solar cell. To improve the conversion efficiency of the HJBC solar cell, we have improved our HJ technology with high-quality a-Si and a low-resistance electrode technology for a back-contact structure. By combining and optimizing the technologies, we developed a HJBC solar cell with a conversion efficiency of 26.3% in 2016, which was a record-breaking efficiency for Si solar cells [5]. In our preliminary experiments of the development of passivation technology, we have confirmed that further improvement of minority carrier lifetime is possible, which reduces the extrinsic recombination loss in the conversion efficiency by an absolute value of ~0.7% from ~1.2%. Small reductions in series resistance loss and optical loss are also possible by a small optimization. Therefore, it is reasonable to expect that a conversion efficiency of 27.1% is achievable by using our state-of-the-art technology [5]. Targeting a conversion efficiency of over 27%, we have improved our HJBC technologies. Now, we reach a conversion efficiency of 26.7% [2]. Besides the cell, using high-efficiency HJBC solar cells and newly developed technologies to minimize the resistance loss of intercell connection in the module and to raise the collection efficiency of the light radiated into the module, we achieved a conversion efficiency of 24.5% efficiency in a module with a size of a building-integrated photovoltaics (BIPV) product [2]. 3. Perovskite/c-Si tandem solar cell One of the low-cost solar cell candidates with efficiencies higher than the theoretical limit of Si is a combination of a perovskite solar cell and a c-Si solar cell. An organic-inorganic hybrid perovskite solar cell has rapidly progressed, and its conversion efficiency has reached 25.2% [3]. A perovskite solar cell is highly attractive as a top cell of a multijunction solar cell owing to its wide- and tunable-bandgap absorber. A record efficiency of 29.15% is reported for a tandem device comprising a perovskite component cell on a Si solar cell [3]. We have also developed perovskite solar cells and examined their multijunction structures with two-terminal and three-terminal tandem as shown in Fig. 2. Our derailed results can be found in ref 6-8. We believe that the improvement of the processes and materials of perovskite solar cells will lead to conversion efficiencies of over 30%. Acknowledgments The authors would like to thank Dr. Rudi Santbergen of Delft University of Technology for performing optical simulations of perovskite/c-Si tandem solar cells. This work was supported in part by the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry of Japan. Reference D.Adachi et al., Appl. Phys. Lett. 107, 23350 (2015).K. Yamamoto et al., Jpn. J. Appl. Phys 57, 08RB20 (2018).https://www.helmholtz-berlin.de/pubbin/news_seite?nid=21020;sprache=en;seitenid=73236M A Green et al., Prog Photovolt Res Appl. 28, 3 (2020).Y, Yoshikawa et al., Nat. Energy 2, 17032 (2017).R. Mishima et al. Appl. Phys. Express 10, 062301 (2017).R. Santbergen et al., Optics Express. 24, A1288 (2016).R. Santbergen et al., IEEE J. Photovolt. 9, 446 (2019). Figure 1

Efficient organic solar cells with low-temperature in situ prepared Ga2O3 or In2O3 electron collection layers

Facile synthesis of an interfacial layer in organic solar cells (OSCs) is important for broadening material designs and upscaling photovoltaic conversion efficiency (PCE). Herein, a mild solution process of spin-coating In(acac)3 and Ga(acac)3 isopropanol precursors followed by low-temperature thermal treatment was developed to fabricate In2O3 and Ga2O3 cathode buffer layers (CBLs). The introduction of In2O3 or Ga2O3 CBLs endows PM6:Y6-based OSCs with outstanding performance and high PCEs of 16.17% and 16.01%, respectively. Comparison studies present that the In2O3 layer possesses a work function (WF) of 4.58 eV, which is more favorable for the formation of ohmic contact compared with the Ga2O3 layer with a WF of 5.06 eV and leads to a higher open circuit voltage for the former devices. Electrochemical impedance spectroscopy was performed to reveal how In2O3 and Ga2O3 affect the internal charge transfer and the origin of their performance difference. Although In2O3 possesses lower series resistance loss, Ga2O3 has a higher recombination resistance, which enhances the device fill factor and compensates for its series resistance loss to some extent. Comparative analysis of the photo-physics of In2O3 and Ga2O3 suggests that both are excellent CBLs for highly efficient OSCs.

Perovskite modules with 99% geometrical fill factor using point contact interconnections design

AbstractThin‐film photovoltaic technology, based on hybrid metal halide perovskites, has achieved 25.2% and 16.1% certified power conversion efficiencies for solar cell and solar module devices, respectively. Still, the gap between power conversion efficiency of small area solar cells and large area solar modules is greater than for any other photovoltaic technology. Analysis of loss mechanisms in n‐i‐p solution processed devices defined layer inhomogeneity loss and inactive area loss as the two most prominent loss mechanisms in upscaling. In this study, we focus on minimizing inactive area loss. We analyze the point contact interconnections design and demonstrate it on perovskite thin‐film solar modules to achieve a geometrical fill factor of up to 99%. Numerical and analytical simulations are utilized to optimize interconnections and solar module design and balance inactive area loss, series resistance loss, and contact resistance loss.

Design Considerations of Ultracapacitor Stack for Optimal Sizing of Energy Storage Systems in Contingency Applications

Ultracapacitors (UCs) today are playing an increasing role in the energy storage systems (ESSs) of several power conversion applications. In this article, a design method for optimal sizing of a UC stack is proposed, which minimizes the overall cost of the ESS. The problem is cast with normalized cost parameters of the ESS subsystem, using which the discharge ratio of the stack is optimized for the given ESS specifications. An iterative design algorithm is proposed which systematically engineers the stack parameters of unit cell capacitance, the number of series cells and parallel strings along with the initial and final stack voltage levels that meet the specified ESS requirements while also supplying the equivalent series resistance (ESR) loss. The iterative sizing process also factors in the maximum power transfer constraint imposed by the ESR to guarantee stable operation of the cost-optimal design even as the stack voltage varies during discharge. The design considerations, optimization framework, ESR effects, and the proposed sizing algorithm are synthesized in a generalized formulation in order to capture the variations in cost and subsystem parameter values that typically vary based on scaling requirements as well as the UC and power converter technology. Experimental results on a 4 kWmin UC stack validate the proposed cost-optimal design algorithm and the ESR induced voltage collapse.

Improvement of carrier collection in Si/a-Si:H nanowire solar cells by using hybrid ITO/silver nanowires contacts

Optoelectronic devices based on high aspect ratio nanowires bring new challenges for transparent electrodes, which can be well addressed by using hybrid structures. Here we demonstrate that a composite contact to radial junction nanowire solar cells made of a thin indium-tin oxide (ITO) layer and silver nanowires greatly improves the collection of charge carriers as compared to a single thick ITO layer by reducing the series resistance losses while improving the transparency. The optimization is performed on p-i-n solar cells comprising of dense non-vertical nanowires with a p-doped c-Si core and an ultra-thin a-Si:H absorption layer grown by plasma-enhanced chemical vapor deposition on glass substrates. The optimal hybrid contact developed in this work is demonstrated to increase the solar cell conversion efficiency from 4.3% to 6.6%.