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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Development of pulsed processes for the manufacture of solar cells

Low-energy ion implantation processes for the automated production of silicon solar cells were investigated. Phosphorus ions at an energy of 10 keV and dose of 2 x 10 to the 15th power/sq cm were implanted in silicon solar cells to produce junctions, while boron ions at 25 keV and 5 x 10 to the 15th power were implanted in the cells to produce effective back surface fields. An ion implantation facility with a beam current up to 4 mA and a production throughput of 300 wafers per hour was designed and installed. A design was prepared for a 100 mA, automated implanter with a production capacity of 100 MW sub e/sq cm per year. Two process sequences were developed which employ ion implantation and furnace or pulse annealing. A computer program was used to determine costs for junction formation by ion implantation and various furnace annealing cycles to demonstrate cost effectiveness of these methods.

Minnucci, J. A.↗
NASA NTRS1984

Investigation of test methods, material properties, and processes for solar cell encapsulants

Photovoltaic (PV) modules consist of a string of electrically interconnected silicon solar cells capable of producing practical quantities of electrical power when exposed to sunlight. To insure high reliability and long term performance, the functional components of the solar cell module must be adequately protected from the environment by some encapsulation technique. The encapsulation system must provide mechanical support for the cells and corrosion protection for the electrical components. The goal of the program is to identify and develop encapsulation systems consistent with the PV module operating requirements of 30 year life and a target cost of $0.70 per peak watt ($70 per square meter) (1980 dollars). Assuming a module efficiency of ten percent, which is equivalent to a power output of 100 watts per square meter in midday sunlight, the capital cost of the modules may be calculated to be $70.00 per square meter. Out of this cost goal, only 20 percent is available for encapsulation due to the high cost of the cells, interconnects, and other related components. The encapsulation cost allocation may then be stated as $14.00 per square meter, included all coatings, pottant and mechanical supports for the cells.

Source record↗
DOE OSTI2021

Homogenous Voltage-Matched Strings Using Three-Terminal Tandem Solar Cells: Fundamentals and End Losses

Strings constructed from three-terminal tandem (3TT) solar cells offer the performance benefits of voltage-matching (which reduces sensitivity to spectral variation), but without the subcell voltage isolation required by four-terminal cells. However, the circuitry for a 3TT string can become complex, making circuit analysis more challenging. Here, we illustrate the essential features of “homogenous” voltage-matched (VM) 3TT strings, for which all 3TT cells in the string are nominally identical (with the same design/doping sequence, such that they can be fabricated on the same manufacturing line). Several representative VM string configurations are explicitly considered, and used to describe the general construction of string I(V) curves. End losses intrinsic to these strings are discussed in detail, along with mitigation strategies to minimize their impact. Our analysis agrees with experimental results for eight-cell strings constructed from GaInP/GaAs 3TT devices.

14 SOLAR ENERGY↗
NASA NTRS1985

High-efficiency silicon solar-cell design and practical barriers

A numerical evaluation technique is used to study the impact of practical barriers, such as heavy doping effects (Auger recombination, band gap narrowing), surface recombination, shadowing losses and minority-carrier lifetime (Tau), on a high efficiency silicon solar cell performance. Considering a high Tau of 1 ms, efficiency of a silicon solar cell of the hypothetical case is estimated to be around 29%. This is comparable with (detailed balance limit) maximum efficiency of a p-n junction solar cell of 30%. Value of Tau is varied from 1 second to 20 micro. Heavy doping effects, and realizable values of surface recombination velocities and shadowing, are then considered in succession and their influence on cell efficiency is evaluated and quantified. These practical barriers cause the cell efficiency to reduce from the maximum value of 29% to the experimentally achieved value of about 19%. Improvement in open circuit voltage V sub oc is required to achieve cell efficiency greater than 20%. Increased value of Tau reduces reverse saturation current and, hence, improves V sub oc. Control of surface recombination losses becomes critical at higher V sub oc. Substantial improvement in Tau and considerable reduction in surface recombination velocities is essential to achieve cell efficiencies greater than 20%.

Mokashi, A.↗
DOE OSTI2021

Flexible and efficient perovskite quantum dot solar cells via hybrid interfacial architecture

All-inorganic CsPbI 3 perovskite quantum dots have received substantial research interest for photovoltaic applications because of higher efficiency compared to solar cells using other quantum dots materials and the various exciting properties that perovskites have to offer. These quantum dot devices also exhibit good mechanical stability amongst various thin-film photovoltaic technologies. We demonstrate higher mechanical endurance of quantum dot films compared to bulk thin film and highlight the importance of further research on high-performance and flexible optoelectronic devices using nanoscale grains as an advantage. Specifically, we develop a hybrid interfacial architecture consisting of CsPbI 3 quantum dot/PCBM heterojunction, enabling an energy cascade for efficient charge transfer and mechanical adhesion. The champion CsPbI3 quantum dot solar cell has an efficiency of 15.1% (stabilized power output of 14.61%), which is among the highest report to date. Building on this strategy, we further demonstrate a highest efficiency of 12.3% in flexible quantum dot photovoltaics.

14 SOLAR ENERGY↗
NASA NTRS1974

The effect of Be/+/ ion implanted exponential and uniform impurity profiles on the electrical characteristics of GaAs solar cells

The high surface recombination velocity is the major deterrent to obtaining efficient GaAs solar cells. If, however, an electric field is built in at the surface, the carriers will be swept away from the surface thus minimizing the surface recombination velocity problem. It has been previously shown theoretically that an exponential impurity distribution in the doped region of the cell results in a built-in electric field. Ion implantation was used to produce solar cells with an exponential impurity profile and cells with uniform profiles. It is shown that cells with an exponential impurity profile have higher open-circuit voltage, fill factors, and spectral response than those with a uniform impurity profile.

Vaidyanathan, K. V.↗
NASA NTRS1981

Fabrication of multijunction high voltage concentrator solar cells by integrated circuit technology

Standard integrated circuit technology has been developed for the design and fabrication of planar multijunction (PMJ) solar cell chips. Each 1 cm x 1 cm solar chip consisted of six n(+)/p, back contacted, internally series interconnected unit cells. These high open circuit voltage solar cells were fabricated on 2 ohm-cm, p-type 75 microns thick, silicon substrates. A five photomask level process employing contact photolithography was used to pattern for boron diffusions, phorphorus diffusions, and contact metallization. Fabricated devices demonstrated an open circuit voltage of 3.6 volts and a short circuit current of 90 mA at 80 AMl suns. An equivalent circuit model of the planar multi-junction solar cell was developed.

Valco, G. J.↗
DOE OSTI2021

Simulating the Effect of p-n Junction Fields on TRPL Transients of Thin-Film CdTe Solar Cells

Bias-dependent time-resolved photoluminescence (TRPL) transients of thin CdTe solar cells were simulated with the goal of characterizing the effect of p-n junction fields on photoluminescence decays. It was found that, although bulk lifetime could be accurately determined in field-free samples, electric field effects in solar cells lead to systematic underestimation of bulk lifetime. Modulating field strength with the application of external bias was found to have a major impact, a result corroborated by experimental data. In particular, p-n junction fields effects were found to be effectively suppressed when a cell is put far into forward bias, enabling accurate measurement of bulk lifetime in p-n junction structures.

CdTe↗
DOE OSTI2024

Solution-processed tungsten diselenide as an inorganic hole transport material for moisture-stable perovskite solar cells in the n-i-p architecture

Some of the obstacles to the commercialization of perovskite solar cells (PSCs) are their long-term moisture stability and material cost of the constituent layers, such as the commonly used spiro-OMeTAD hole transport layer (HTL). Replacing the spiro-OMeTAD with low-cost inorganic hole transport materials (HTMs) are important to further elevate the attractiveness of PSCs for commercialization. Perovskite-compatible, solution-exfoliated two-dimensional (2D) transition metal dichalcogenides (TMDCs) are being considered as viable candidates for inorganic HTMs. We consider one such TMDC, WSe 2 which was chemically exfoliated using dichlorobenzene (DCB), a perovskite-compatible solvent, as it was integrated with triple cation perovskite absorbers within the solar cell stack. Here, the WSe 2 HTL required heat treatment processes to be maintained below 100°C in order to preserve the integrity of the underlying perovskite; despite this lower temperature post treatment process, the structural morphology of the film revealed its dense and pinhole-free nature. Temperature-dependent transport studies conducted on the WSe 2 film provided evidence of its semiconducting character and its ability to extract holes well from the underlying triple-cation Cs 0.05 FA 0.79 MA 0.16 PbI 2.45 Br 0.55 absorber. The inorganic HTL offered better environmental stability in moisture-rich environments of up to 60% relative humidity, in comparison to spiro-OMeTAD HTL-based devices which degraded faster as a result of pinholes

14 SOLAR ENERGY↗
DOE OSTI2022

Polymerized Small Molecular Acceptor with Branched Side Chains for All Polymer Solar Cells with Efficiency over 16.7%

The power conversion efficiencies (PCEs) of small molecule acceptor (SMA)-based organic solar cells have already exceeded 18%. However, the development of polymer acceptors still lags far behind their SMA counterparts mainly due to the lack of efficient polymer acceptors. In this work, a series of polymer acceptors named PY-X (with X being the branched alkyl chain) are designed and synthesized by employing the same central core with the SMA L8-BO but with different branched alkyl chains on the pyrrole motif. It is found that the molecular packing of SMA-HD featuring 2-hexyldecyl side chain used in the synthesis of PY-HD is similar to L8-BO, in which the branched alkyl chains lead to condensed and high-order molecular assembly in SMA-HD molecules. When combined with PM6, PY-HD-based all polymer solar cell (all-PSC) exhibits a high PCE of 16.41%, representing the highest efficiency for the binary all-PSCs. Moreover, the side-chain modification on the pyrrole site position further improves the performance of the all-PSCs, and the PY-DT-based device delivers a new record high efficiency of 16.76% (certified as 16.3%). The work provides new insights for understanding the structure–property relationship of polymer acceptors and paves a feasible avenue to develop efficient conjugated polymer acceptors.

14 SOLAR ENERGY↗
NASA NTRS1975

The high intensity solar cell - Key to low cost photovoltaic power

This paper discusses the problems associated with conventional solar cells at high intensities and presents the design considerations and performance characteristics of the 'high intensity' (HI) solar cell which appears to eliminate the major problems. Test data obtained at greater than 250 AM1 suns gave a peak output power density of 2 W per sq cm at an efficiency exceeding 6% with an unoptimized cell operating at over 100 C. It appears that operation at 1000 AM1 suns at efficiencies greater than 10% is possible. At 1000 AM1 suns and 10% efficiency, the HI cell manufacturing cost is estimated to be $0.25/watt, with multi-megawatt annual production capability already existing within the industrial sector. A high intensity solar system was also analyzed to determine its cost effectiveness and to assess the benefits of further improving HI cell efficiency.

Sater, B. L.↗
DOE OSTI2022

Phosphorus replenishment to improve the contact resistivity of light-induced Al contacts on Si solar cells

A method to repair laser-induced phosphorus loss from the n-type emitter of Si solar cells during light-induced Al plating is demonstrated. The ability to add a water-reactive phosphorus compound, PCl 5 , into the Al plating bath gives a unique advantage to Al over Cu for front contacts on Si solar cells. The contact resistivity between light-induced Al and Si emitter is reduced to as low as 0.1 mΩ-cm 2 . Cyclic voltammetry performed on a plating bath composed of 81 wt% 1-ethyl-3-methylimidazolium tetrachloroaluminate, 19 wt% AlCl 3 , and 0.2 wt% PCl 5 reveals multiple reduction reactions of PCl 5 , although incomplete decomposition of PCl 5 is possible. A decrease in nucleation loop size during cyclic voltammetry is also observed suggesting that PCl 5 , while being consumed, modifies the growth mechanism during Al plating. Structural analysis confirms that the addition of PCl 5 produces an Al film which is levelized and compact. Here, a pulsed voltage profile coupled with chemical analysis verifies that phosphorus incorporation is electrolytically activated and is likely the cause for the low contact resistivity.

14 SOLAR ENERGY↗
DOE OSTI2024

Mixed Self-Assembled Monolayers for High-Photovoltage Tin Perovskite Solar Cells

Self-assembled monolayers (SAMs) are used as potent hole transport layers (HTLs) in lead-based perovskite solar cells, enabling large quasi-Fermi level splitting for high photovoltage (>1.1 V) with a deficit of <0.5 V. However, tin-based perovskite solar cells (TPSCs) with SAM HTLs suffer from low photovoltage (<0.65 V) with a deficit of >0.7 V. Herein we employ a holistic approach to tackle this significant challenge by designing a mixed SAM, engineering a compatible tin perovskite thin film, and leveraging an efficient electron transport layer. Consequently, high photovoltage of 0.829 V is achieved with an efficiency of 9.4%, which is a record to our knowledge among TPSCs using SAMs as sole HTLs. Finally, while SAMs have been little used in TPSCs thus far, our holistic approach should catalyze their future advancements toward outperformance.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Polymeric Electron-Selective Contact for Crystalline Silicon Solar Cells with an Efficiency Exceeding 19%

Carrier-selective contacts have become a prominent path forward toward efficient crystalline silicon (c-Si) photovoltaics. Among the proposed contacting materials, organic materials may offer simplified and low-cost processing compared with typical vacuum deposition techniques. In this paper, branched polyethylenimine (b-PEI) is presented as an electron-transport layer (ETL) for c-Si solar cells. The incorporation of a b-PEI interlayer between c-Si(n) and Al leads to a low contact resistivity of 24 mΩ cm 2 . A silicon heterojunction solar cell integrated with b-PEI is demonstrated achieving a power conversion efficiency of 19.4%, which improves the benchmark efficiency of a c-Si solar cell with an organic ETL. This electron selectivity of b-PEI is attributed to its Lewis basicity, i.e., electron-donating ability, promoting favorable band bending at the c-Si surface for electron transport. Moreover, several other Lewis base polymers perform as efficient ETLs in organic/c-Si hybrid devices, indicating Lewis basicity could be a guideline for future organic ETL design.

14 SOLAR ENERGY↗
NASA NTRS1987

Self-consistent calculations and design considerations for a GaAs nipi doping superlattice solar cell

The authors present design constraints which show that a previously proposed GaAs nipi doping superlattice solar cell structure would not work as an efficient space solar cell. A structure based on the CLEFT process, which shows promise of being an efficient cell with very high radiation tolerance, is proposed. In order to test theoretically its viability and to optimize its design, self-consistent quantum mechanical calculations were made for a number of thicknesses of the n, i, and p layers and the dopings in the n and p layers. These results show that: 1) an i layer is not necessary; in fact, its presence makes it difficult to satisfy one of the key constraints; 2) a near-optimum design with 750-A thick n and p layers with dopings of 2.5E18/cu cm and a selective contact separation of 20 microns would yield both high efficiency and very high radiation tolerance.

Clark, Ralph O.↗
DOE OSTI2022

Solar cell efficiency tables (Version 60)

Abstract Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2022 are reviewed. An appendix describing temporary electrical contacting of large‐area solar cells approaches and terminology is also included.

14 SOLAR ENERGY↗