Author: Marc-Roland Kaelin
Publisher:
ISBN:
Category :
Languages : en
Pages : 96

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Author: Wei Wang
Publisher:
ISBN:
Category : Chalcopyrite
Languages : en
Pages : 107

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CuInGaSe2 (CIGS), a promising thin film solar cell material, has gained lots of attention in decades due to its high energy conversion efficiency and potential lower manufacture cost over conventional Si solar cells. As a cheaper processing method compared to vacuum-based techniques, solution-based deposition has been successfully applied to fabricate electronic devices, such as transistors and solar cells. In my research, CIGS thin film solar cells with energy conversion efficiencies up to 8.01% were successfully fabricated using newly developed air-stable, low-cost inks. The inks consist of commercially available, low-cost compounds and solvents and can be processed using a variety of printing and coating techniques. More importantly, it can synthesize CIGS films free of contamination from copper selenides and amorphous carbon which are common issues for most of solution-based techniques. Besides, high-quality micrometer-sized CIGS films were obtained by using our enhanced selenization approach. Various characterization techniques were employed to qualitatively and quantitatively characterize the semiconductor materials and devices fabricated by this process. The mechanism for the transformation from metal salt precursor films to CIGS absorber thin films and the influence of ink composition and selenium vapour pressure on absorber film quality and photovoltaic device performance were investigated and discussed.

Author: Stephen Thacker Connor
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 99

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In recent years, the field of photovoltaics has become increasingly important due to rising energy demand and climate change. While most solar cells are currently composed of crystalline silicon, devices with thinner films of inorganic absorber materials might allow production at a greater scale due to their lower materials cost. In particular, thin films of CuInS2 are promising solar absorber materials due to their high efficiencies and low required thicknesses. However, the fabrication of thin film solar cells currently requires expensive vacuum techniques. As an alternative, solution-based deposition techniques have been proposed as a route to low-cost and high-throughput electronic device fabrication. I have studied how film growth depends on solutuion deposited precursor film quality, with the goal of producing large grained films of CuInS2 through solution processing. In the first approach, we used solvothermal decomposition of organometallic precursors at moderate temperatures to produce nanoparticles of CuInS2. Thin films of these nanoparticles were cast onto molybdenum coated glass and further processed to create CuInS2 solar cells. We found that performance was dependent on film porosity, grain size, and stoichiometry of the nanoparticles. Films with grain sizes of ~200nm were attained, from which 1.3% efficient solar cells were made. In addition, we showed that this synthesis could be extended to produce CuInS2 nanoparticles with partial substitution of Fe, Zn, and Ga. In the second approach, we synthesized an air-stable hybrid organometallic/nanoparticle ink at room temperature in ambient conditions through a vulcanization reaction. This ink could be coated onto substrates in smooth layers, and further reactive annealing formed large grained CuInS2 films. This process was characterized, and a correlation between residual carbon and grain growth was found. Additionally, the chemical transformation between precursor layers and final sulfide thin film was analyzed, with an emphasis on the difference between sulfurization and selenization. We demonstrated that the sulfurization process was producing morphological defects due to its nucleation limited growth mechanism. However, it was modified to more closely resemble the diffusion limited selenization mechanism, thus producing flat films of CuInS2 with grain sizes of ~500nm.

Author: Christopher J. Hibberd
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Solar photovoltaic modules provide clean electricity from sunlight but will not be able tocompete on an open market until the cost of the electricity they produce is comparable to thatproduced by traditional methods. At present, modules based on crystalline silicon wafer solarcells account for nearly 90% of photovoltaic production capacity. However, it is anticipatedthat the ultimate cost reduction achievable for crystalline silicon solar cell production will besomewhat limited and that thin film solar cells may offer a cheaper alternative in the longterm. The highest energy conversion efficiencies reported for thin film solar cells have beenfor devices based around chalcopyrite Cu(In, Ga)(Se, S)2 photovoltaic absorbers. The most efficient Cu(In, Ga)(Se, S)2 solar cells contain absorber layers deposited by vacuumco-evaporation of the elements. However, the cost of ownership of large area vacuumevaporation technology is high and may be a limiting factor in the cost reductions achievablefor Cu(In, Ga)(Se, S)2 based solar cells. Therefore, many alternative deposition methods areunder investigation. Despite almost thirty companies being in the process of commercialisingthese technologies there is no consensus as to which deposition method will lead to the mostcost effective product. Non-vacuum deposition techniques involving powders and chemical solutions potentiallyoffer significant reductions in the cost of Cu(In, Ga)(Se, S)2 absorber layer deposition ascompared to their vacuum counterparts. A wide range of such approaches has beeninvestigated for thirty years and the gap between the world record Cu(In, Ga)(Se, S)2 solarcell and the best devices containing non-vacuum deposited absorber layers has closedsignificantly in recent years. Nevertheless, no one technique has demonstrated its superiorityand the best results are still achieved with some of the most complex approaches. The work presented here involved the development and investigation of a new process forperforming one of the stages of non-vacuum deposition of Cu(In, Ga)(Se, S)2 absorber layers. The new process incorporates copper into an initial Group III-VI precursor layer, e.g. indiumgallium selenide, through an ion exchange reaction performed in solution. The ion exchangereaction requires only very simple, low-cost equipment and proceeds at temperatures over1000?C lower than required for the evaporation of Cu under vacuum. In the new process, indium (gallium) selenide initial precursor layers are immersed insolutions containing Cu ions. During immersion an exchange reaction occurs and Cu ionsfrom the solution exchange places with Group III ions in the layer. This leads to theformation of an intimately bonded, laterally homogeneous copper selenide? indium (gallium)selenide modified precursor layer with the same morphology as the initial precursor. These modified precursor layers were converted to single phase chalcopyrite CuInSe2 andCu(In, Ga)Se2 by annealing with Se in a tube furnace system. Investigation of the annealingtreatment revealed that a series of phase transformations, beginning at low temperature, leadto chalcopyrite formation. Control of the timing of the Se supply was demonstrated toprevent reactions that were deemed detrimental to the morphology of the resultingchalcopyrite layers. When vacuum evaporated indium (gallium) selenide layers were used asinitial precursors, solar cells produced from the absorber layers exhibited energy conversionefficiencies of up to 4%. While these results are considered promising, the devices werecharacterised by very low open circuit voltages and parallel resistances. Rapid thermal processing was applied to the modified precursor layers in an attempt tofurther improve their conversion into chalcopyrite material. Despite only a small number ofsolar cells being fabricated using rapid thermal processing, improvements in open circuitvoltage of close to 150mV were achieved. However, due to increases in series resistance andreductions in current collection only small increases in solar cell efficiency were recorded. Rapid thermal processing was also used to demonstrate synthesis of single phase CuInS2from modified precursor layers based on non-vacuum deposited indium sulphide. Non-vacuum deposition methods provide many opportunities for the incorporation ofundesirable impurities into the deposited layers. Analysis of the precursor layers developedduring this work revealed that alkali atoms from the complexant used in the ion exchangebaths are incorporated into the precursor layers alongside the Cu. Alkali atoms exhibitpronounced electronic and structural effects on Cu(In, Ga)Se2 layers and are beneficial in lowconcentrations. However, excess alkali atoms are detrimental to Cu(In, Ga)Se2 solar cellperformance and the problems encountered with cells produced here are consistent with theeffects reported in the literature for excess alkali incorporation. It is therefore expected thatfurther improvements in solar cell efficiency might be achieved following reformulation ofthe ion exchange bath chemistry.

Author: Stefan Jost
Publisher:
ISBN:
Category :
Languages : en
Pages : 155

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Author: Suresh Babu Gandham
Publisher: LAP Lambert Academic Publishing
ISBN: 9783845423241
Category :
Languages : en
Pages : 140

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Solar cells have high potential as an alternative energy technology for fulfilling the energy needs. It has the additional advantage being environmentally friendly. Solar photovoltaic cells based on single crystalline Si are prohibitively expensive. Hence, researchers are looking for solar cell materials which are cheap and abundant. Successful thin film solar cells based on CuInGaSe2 uses costly and non-abundant elements like In & Ga, CdTe uses toxic material Cd. To overcome these associated difficulties, we have chosen Cu2ZnSnSe4 thin films which contain elements which are relatively cheap, abundant and less toxic. In this book a brief review of the solar cell absorber layers were presented along with their successes and present market values. Focus is mainly concentrated on the qualities and suitability of Cu2ZnSnSe4 thin films as absorber layers. Preparation (using co-evaporation)and characterization details of this materials are highlighted. Parameters like optimum deposition conditions and ratio between elements re given. Brief description of window preparation and characterization is also presented along with the scope for future work to encourage the readers.

Author: J. C. Keane
Publisher:
ISBN:
Category :
Languages : en
Pages : 5

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We present a summary of our work on the preparation of CuInGaSe2 (CIGS) absorbers that has led to fabricating record-efficiency solar cells. The use of the three-stage process in conjunction with composition monitoring facilitates the fabrication of solar cells with efficiencies between 18% and 19.5% for absorber bandgap in the range of 1.1-1.2 eV. We describe our recent results in reducing absorber thickness and low-temperature deposition. Our preliminary results on absorbers grown from low-purity source materials show promise of reducing the cost of fabricating the absorber.

Author: Stephen Thacker Connor
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
In recent years, the field of photovoltaics has become increasingly important due to rising energy demand and climate change. While most solar cells are currently composed of crystalline silicon, devices with thinner films of inorganic absorber materials might allow production at a greater scale due to their lower materials cost. In particular, thin films of CuInS2 are promising solar absorber materials due to their high efficiencies and low required thicknesses. However, the fabrication of thin film solar cells currently requires expensive vacuum techniques. As an alternative, solution-based deposition techniques have been proposed as a route to low-cost and high-throughput electronic device fabrication. I have studied how film growth depends on solutuion deposited precursor film quality, with the goal of producing large grained films of CuInS2 through solution processing. In the first approach, we used solvothermal decomposition of organometallic precursors at moderate temperatures to produce nanoparticles of CuInS2. Thin films of these nanoparticles were cast onto molybdenum coated glass and further processed to create CuInS2 solar cells. We found that performance was dependent on film porosity, grain size, and stoichiometry of the nanoparticles. Films with grain sizes of ~200nm were attained, from which 1.3% efficient solar cells were made. In addition, we showed that this synthesis could be extended to produce CuInS2 nanoparticles with partial substitution of Fe, Zn, and Ga. In the second approach, we synthesized an air-stable hybrid organometallic/nanoparticle ink at room temperature in ambient conditions through a vulcanization reaction. This ink could be coated onto substrates in smooth layers, and further reactive annealing formed large grained CuInS2 films. This process was characterized, and a correlation between residual carbon and grain growth was found. Additionally, the chemical transformation between precursor layers and final sulfide thin film was analyzed, with an emphasis on the difference between sulfurization and selenization. We demonstrated that the sulfurization process was producing morphological defects due to its nucleation limited growth mechanism. However, it was modified to more closely resemble the diffusion limited selenization mechanism, thus producing flat films of CuInS2 with grain sizes of ~500nm.

Author: Ashwani Kaul
Publisher:
ISBN:
Category :
Languages : en
Pages : 123

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Thin film solar cells have the potential to be an important contributor to the world energy demand in the 21st century. Among all the thin film technologies, CuInGaSe2 (CIGS) thin film solar cells have achieved the highest efficiency. However, the high price of photovoltaic (PV) modules has been a major factor impeding their growth for terrestrial applications. Reduction in cost of PV modules can be realized by several ways including choosing scalable processes amenable to large area deposition, reduction in the materials consumption of active layers, and attaining faster deposition rates suitable for in-line processing. Selenization-sulfurization of sputtered metallic Cu-In-Ga precursors is known to be more amenable to large area deposition. Sputter-deposited molybdenum thin film is commonly employed as a back contact layer for CIGS solar cells. However, there are several difficulties in fabricating an optimum back contact layer. It is known that molybdenum thin films deposited at higher sputtering power and lower gas pressure exhibit better electrical conductivity. However, such films exhibit poor adhesion to the soda-lime glass substrate. On the other hand, films deposited at lower discharge power and higher pressure although exhibit excellent adhesion show lower electrical conductivity. Therefore, a multilayer structure is normally used so as to get best from the two deposition regimes. A multi-pass processing is not desirable in high volume production because it prolongs total production time and correspondingly increases the manufacturing cost. In order to make manufacturing compliant with an in-line deposition, it is justifiable having fewer deposition sequences. Thorough analysis of pressure and power relationship of film properties deposited at various parameters has been carried out. It has been shown that it is possible to achieve a molybdenum back contact of desired properties in a single deposition pass by choosing the optimum deposition parameters. It is also shown that the film deposited in a single pass is actually a composite structure. CIGS solar cells have successfully been completed on the developed single layer back contact with National Renewable Energy Laboratory (NREL) certified device efficiencies [greater than]11%. The optimization of parameters has been carried out in such a way that the deposition of back contact and metallic precursors can be carried out in identical pressure conditions which is essential for in-line deposition without a need for load-lock. It is know that the presence of sodium plays a very critical role during the growth of CIGS absorber layer and is beneficial for the optimum device performance. The effect of sodium location during the growth of the absorber layer has been studied so as to optimize its quantity and location in order to get devices with improved performance. NREL certified devices with efficiencies [greater than]12% have been successfully completed.

Author: Jan-Peter Bäcker
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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