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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Thin silicon solar cell performance characteristics

Refined techniques for surface texturizing, back surface field and back surface reflector formation were evaluated for use with shallow junction, single-crystal silicon solar cells. Each process was characterized individually and collectively as a function of device thickness and bulk resistivity. Among the variables measured and reported are open circuit voltage, short circuit current and spectral response. Substantial improvements were obtained by the utilization of a low cost aluminum paste process to simultaneously remove the unwanted n(+) diffused region, form the back surface field and produce an ohmic contact metallization. The highly effective BSF which results from applying this process has allowed fabrication of cells 0.05 mm thick with initial outputs as high as 79.5 mW/4 sq cm (28 C, AM0) and superior electron radiation tolerance. Cells of 0.02 mm to 0.04 mm thickness have been fabricated with power to mass ratios well in excess of 2 watts per gram.

Gay, C. F.↗
NASA NTRS1976

A program continuation to develop processing procedures for advanced silicon solar cells

Shallow junctions, aluminum back surface fields and tantalum pentoxide (Ta205) antireflection coatings coupled with the development of a chromium-palladium-silver contact system, were used to produce a 2 x 4 cm wraparound contact silicon solar cell. One thousand cells were successfully fabricated using batch processing techniques. These cells were 0.020 mm thick, with the majority (800) made from nominal ten ohm-cm silicon and the remainder from nominal 30 ohm-cm material. Unfiltered, these cells delivered a minimum AMO efficiency at 25 C of 11.5 percent and successfully passed all the normal in-process and acceptance tests required for space flight cells.

Avery, J. E.↗
DOE OSTI2020

Surface Ligand Management Aided by a Secondary Amine Enables Increased Synthesis Yield of CsPbI 3 Perovskite Quantum Dots and High Photovoltaic Performance

Lead-halide perovskite quantum dots (PQDs) or more broadly, nanocrystals possess advantageous features for solution-processed photovoltaic devices. The nanocrystal surface ligands play a crucial role in the transport of photogenerated carriers and ultimately affect the overall performance of PQD solar cells. Here, significantly improved CsPbI 3 PQD synthetic yield and solar-cell performance through surface ligand management are demonstrated. The treatment of a secondary amine, di- n -propylamine (DPA), provides a mild and efficient approach to control the surface ligand density of PQDs, which has an apparently different working mechanism compared to previously reported surface treatments. Using an optimal DPA concentration, the treatment can simultaneously remove both long-chain insulating surface ligands of oleic acid and oleylamine, even for unpurified PQDs with high ligand density. As a result, the electrical coupling between PQDs is enhanced, leading to improved charge transport, reduced carrier recombination, and a high power conversion efficiency approaching 15% for CsPbI 3 -PQD-based solar cells. In addition, the production yield of CsPbI 3 PQDs can be increased by a factor of 8. These results highlight the importance of developing new ligand-management strategies, specifically for emerging PQDs to achieve scalable and high-performance perovskite-based optoelectronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS1972

The observation of damage regions produced by neutron irradiation in lithium-doped silicon solar cells.

Study regions of lattice disorder produced in lithium-doped float-zone melted n/p-type silicon solar cells by irradiation with monoenergetic neutrons at doses between 10 to the 10th and 10 to the 13th per cu cm. The defect regions were revealed by chemically etching the surface of the solar cells and by observing carbon replicas in an electron microscope. It was found that the defect density increased with increasing irradiation dose and increased lithium content, whereas the average defect diameter was found to decrease. From thermal annealing experiments it was found that in the lithium-doped material the defect structure was stable at temperatures between 300 and 1200 K. This was found to be in contrast to the undoped material where at the lowest doses considerable annealing was observed to occur. These results are discussed in terms of the theoretical predictions and models of defect clusters proposed by Gossick (1959) and Crawford and Cleland (1959).

Ghosh, S.↗
DOE OSTI2022

On the surface passivating principle of functional thiol towards efficient and stable perovskite nanocrystal solar cells

Inorganic halide perovskite nanocrystals (PNCs) have demonstrated promising potential for solar cell applications. However, the lability of photoactive CsPbI3 phase under ambient conditions, coupled with considerable amounts of surface defects induced during solidification process, have impeded achieving high performances and longevities of the PNC-based solar cells. Post-treatment of the PNCs with organic ligands has been proposed as an efficient strategy for surface passivation, which, however, still relies on the binding actions of typical functional groups towards surface defects (especially, carboxylates onto iodine vacancies). Herein, we uncover that thiolate, a deprotonated form of thiol, renders distinctive binding feasibility towards iodine vacancies at the CsPbI3 PNC surface, compared with those of typical functional groups. By treating the PNC solid with deprotonated cysteine as a ligand, the surface defects are comprehensively passivated. The solar cells with the modified PNC films demonstrate an excellent PCE of 15.5 % and improved device longevity (77 % of initial PCE over 2 months) under ambient conditions. Our work not only elucidates the chemical principles of thiol on the binding with PNC surface, but also corroborates the power of thiolate as a promising strategy to develop high performances and improved longevity of solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Electrochemical quantification of phosphonic acid passivated surface sites of NiO x for perovskite solar cells

Nickel oxide (NiO x ) is among the few p-type metal oxide semiconductors considered a strong candidate for hole transport layers in halide perovskite solar cells (PSCs). However, its reactivity with perovskite ions poses significant challenges to achieving high efficiency and long-term stability. Here, we investigate passivation of detrimental reactive surface sites on NiO x by carbazole phosphonic acids. We leverage electrochemical cyclic voltammetry (CV) of NiO x electrodes as a proxy measure for the redox activity that afflicts PSCs. From the CVs, we derive a metric, N (units cm −2 ), that relates to the number of redox active sites on NiO x surfaces. We observe a statistically significant negative correlation between PSC efficiency and N-value that indicates PSCs are more efficient on NiO x with lower electrochemical reactivity. The new mechanistic insight into NiO x passivation demonstrates it requires a reducing agent and Brønsted acid combination, providing a broadly applicable approach for evaluating and enhancing the stability and performance of NiO x -based interfaces in photovoltaics.

14 SOLAR ENERGY↗
NASA NTRS1978

Silicon Solar Cell Process Development, Fabrication and Analysis

Ribbon to Ribbon (RTR) solar cells processed from polycrystalline feedstock showed maximum AMO efficiency of 5.6%. Solar cells from single crystalline feedstock showed slightly higher efficiency than those from polycrystalline feedstock, indicating maximum efficiency of about 6.6% with SiO AR coating. Single crystalline control cells gave 11-12% AMO efficiencies demonstrating that the poor performance of the RTR solar was due to the low quality of material itself. Dendritic web solar cells from the standard process showed maximum AMO efficiency of 9.8% while efficiency of control solar cells were around 11-12%. Web solar cells from back surface field (BSF) process indicated maximum AMO efficiency of 10.9%. Some improvement in open circuit voltage was noticed from the BSF process. Small light spot scanning experiments were carried out on the solar cells from Wacker Silso, EFG, RTR, and dendritic web ribbons. Photoresponse results provided information on localized cell performance and grain size in polycrystalline material, and agreed quite well with the cell performance data, such as efficiency, minority carrier diffusion length, and spectral response.

Yoo, H. I.↗
DOE OSTI2022

Surface reaction for efficient and stable inverted perovskite solar cells

We report perovskite solar cells (PSCs) with an inverted structure (often referred to as the p-i-n architecture) are attractive for future commercialization due to their easily scalable fabrication, reliable operation, and compatibility with a wide range of perovskite-based tandem device architectures. However, the power conversion efficiency (PCE) of p-i-n PSCs falls behind n-i-p (or normal) structure counterparts. This large performance gap could undermine efforts to adopt p-i-n architectures, despite their other advantages. Given the remarkable advances in perovskite bulk materials optimization over the past decade, interface engineering has become the most important strategy to push PSC performance to its limit. Here, we report a reactive surface engineering approach based on a simple post-growth treatment of 3-(Aminomethyl)pyridine (3-APy) on top of a perovskite thin film. First, the 3-APy molecule selectively reacts with surface FA+, reducing perovskite surface roughness and surface potential fluctuations associated with surface steps/terraces. Second, the reaction product on the perovskite surface decreases the formation energy of charged iodine-vacancies, leading to effective n-type doping with a reduced work function in the surface region. With this reactive surface engineering, the resulting p-i-n PSCs obtained a PCE over 25%, along with retaining 87% of the initial PCE after over 2400 h of one-sun operation at about 55 degrees C in air.

14 SOLAR ENERGY↗
NASA NTRS1979

The importance of surface recombination and energy-bandgap narrowing in p-n-junction silicon solar cells

Experimental data demonstrating the sensitivity of open-circuit voltage to front-surface conditions are presented for a variety of p-n-junction silicon solar cells. Analytical models accounting for the data are defined and supported by additional experiments. The models and the data imply that a) surface recombination significantly limits the open-circuit voltage (and the short-circuit current) of typical silicon cells, and b) energy-bandgap narrowing is important in the manifestation of these limitations. The models suggest modifications in both the structural design and the fabrication processing of the cells that would result in substantial improvements in cell performance. The benefits of one such modification - the addition of a thin thermal silicon-dioxide layer on the front surface - are indicated experimentally.

Fossum, J. G.↗
NASA NTRS1979

Detection of hairline cracks in textured silicon solar cells

Using a focused laser scanner, the optical technique described in the present paper can be used to detect hairline cracks of the type occurring in solar cells subjected to surface texturing. The technique is capable of detecting cracks of the order of a few microns, which, otherwise, can be observed only under high magnification using an optical microscope. The technique consists of scanning a solar cell with a finely focused laser beam and recording the photoresponse (short circuit current or open circuit voltage) as a function of beam position. The presence of a crack is manifested by a sharp dip in the photoresponse.

Sopori, B. L.↗
NASA NTRS1990

Buried homojunction solar cells formed in p-InP during sputter deposition and hydrogen plasma processing

Although it is apparent that direct current (DC) magnetron sputter deposition of indium tin oxide (ITO) leads to the formation of a buried homojunction in single-crystal p-type InP, the actual mechanism of type conversion of the InP surface is not clear. Since sputter deposition of In2O3 has also led to high-quality cells, it appears that Sn is not the cause of type conversion. To investigate the junction formation process further, experiments involving the use of a pure hydrogen plasma have been performed, resulting in type conversion of Fe-doped InP surfaces and in solar cells with efficiencies over 16 percent (global). The results confirm that sputter deposition is not necessary to form this type of buried homojunction solar cell, and they suggest a fabrication process that may be used with other relevant photovoltaic materials.

Gessert, T. A.↗
NASA NTRS1979

Solar cell with improved N-region contact and method of forming the same

An improved solar cell, and method of forming the same are disclosed. It is characterized by a semiconductor silicon wafer of P-type material having diffused therein a shallow N-type region. A sintered silver contact is affixed to the surface of the N-type region at the outer surface. The improved solar cell is formulated from silver powder blended with silver metaphosphate for establishing a zone of increased carrier concentration. An aluminum or silver-aluminum alloy contact is affixed to the P-type wafer at the outer surface opposite the N-type region.

Bube, K. R.↗
NASA NTRS1980

Electrostatic bonding of thin (approximately 3 mil) 7070 cover glass to Ta2O5 AR-coated thin (approximately 2 mil) silicon wafers and solar cells

Electrostatic bonding (ESB) of thin (3 mil) Corning 7070 cover glasses to Ta2O5 AR-coated thin (2 mil) silicon wafers and solar cells is investigated. An experimental program was conducted to establish the effects of variations in pressure, voltage, temperature, time, Ta2O5 thickness, and various prebond glass treatments. Flat wafers without contact grids were used to study the basic effects for bonding to semiconductor surfaces typical of solar cells. Solar cells with three different grid patterns were used to determine additional requirements caused by the raised metallic contacts.

Egelkrout, D. W.↗
NASA NTRS2005

Manufacture of Solar Cells on the Moon

In support of the space exploration initiative a new architecture for the production of solar cells on the lunar surface is devised. The paper discusses experimental data on the fabrication and properties of lunar glass substrates, evaporated lunar regolith thin film (antireflect coatings and insulators), and preliminary attempts in the fabrication of thin film (silicon/II-VI) photovoltaic materials on lunar regolith substrates. A conceptual design for a solar powered robotic rover capable of fabricating solar cells directly on the lunar surface is provided. Technical challenges in the development of such a facility and strategies to alleviate perceived difficulties are discussed. Finally, preliminary cost benefit ratio analysis for different in situ solar cell production scenarios (using exclusively in-situ planetary resources or hybrid) are discussed.

Freundich, Alex↗
NASA NTRS1994

Hypervelocity Impact Testing of Space Station Freedom Solar Cells

Solar array coupons designed for the Space Station Freedom electrical power system were subjected to hypervelocity impacts using the HYPER facility in the Space Power Institute at Auburn University and the Meteoroid/Orbital Debris Simulation Facility in the Materials and Processes Laboratory at the NASA Marshall Space Flight Center. At Auburn, the solar cells and array blanket materials received several hundred impacts from particles in the micron to 100 micron range with velocities typically ranging from 4.5 to 10.5 km/s. This fluence of particles greatly exceeds what the actual components will experience in low earth orbit. These impacts damaged less than one percent of total area of the solar cells and most of the damage was limited to the cover glass. There was no measurable loss of electrical performance. Impacts on the array blanket materials produced even less damage and the blanket materials proved to be an effective shield for the back surface of the solar cells. Using the light gas gun at MSFC, one cell of a four cell coupon was impacted by a 1/4 inch spherical aluminum projectile with a velocity of about 7 km/s. The impact created a neat hole about 3/8 inch in diameter. The cell and coupon were still functional after impact.

Christie, Robert J.↗
NASA NTRS1977

Theoretical effects of surface diffused region lifetime models on silicon solar cells

A computer simulation of silicon solar cells has indicated that the combination of band gap reduction due to heavy doping and certain spatial forms of lifetime dependence can combine to form severe limitations on the open-circuit voltage of such cells. The interaction of these effects tends to shift the active region of the diffused surface layer away from the injecting junction, resulting in an increase in the current density injected into the surface region. Reductions in open circuit voltage as great as 10% over models which do not include these effects can be seen.

Dunbar, P. M.↗
DOE OSTI2021

Distinguishing bulk and surface recombination in CdTe thin films and solar cells using time-resolved terahertz and photoluminescence spectroscopies

Understanding the nature of recombination and its dependence on defects and interfaces is essential for engineering materials and contacts for higher open circuit voltage (V oc ) and power conversion efficiency in photovoltaic (PV) devices. Time-resolved photoluminescence (TRPL) has conventionally been used to evaluate recombination, but carrier redistribution often dominates the response at short times. In this work, we report on the quantification of carrier dynamics and recombination mechanisms by complementary use of both time-resolved terahertz spectroscopy (TRTS) and TRPL combined with numerical modeling of the continuity equations and Poisson’s equation. We have demonstrated this approach using CdTe thin films. A thin film stack with CdTe fabricated by vapor transport deposition and treated with CdCl 2 exhibited a bulk lifetime of 1.7 ± 0.1 ns, negligible CdTe/CdS interface recombination velocity, and back surface recombination velocity of 6.3 ± 1.3 x10 4 cm/s. In contrast, a film stack without CdCl 2 treatment had a bulk lifetime of only 68 ± 12 ps and a higher interface recombination velocity of 4 ± 2 x10 8 cm/s. By determining the locus and mechanisms of performance-limiting recombination, we can accelerate the development of thin-film PVs with higher V oc and efficiency. While the method has been demonstrated here using CdTe, it is also applicable to perovskites, Cu(InGa)Se 2 , Cu2ZnSn(S,Se) 4, and emerging technologies.

14 SOLAR ENERGY↗