The impact of the Ag particle ͑metal powder in the screen printed paste͒ size on the quality of Ag thick-film ohmic contacts to high-sheet-resistance emitters of Si solar cells is investigated. Spherical particle size was varied in the range of 0.10-10 m ͑ultrafine to large͒. Even though ultrathin glass regions are achieved for the large particle paste, giving low specific contact resistance ͑ c ͒, secondary ion mass spectroscopy measurements showed a higher Ag concentration ͑Ͼ10 15 cm −3 ͒ at the p-n junction that increased the junction leakage current ͑J o2 ͒ and decreased the V oc by ϳ7 mV and fill factor ͑FF͒ by ϳ0.02. Pastes with ultrafine Ag particles generally produced a thick glass layer at the Ag-Si contact interface, which increased c and series resistance ͑R s ͒ ͑ജ1 ⍀ cm 2 ͒, and lowered the FF by ϳ0.03. Small to medium size Ag particles in the paste produced thin glass regions and many regularly distributed Ag crystallites at the contact interface. This resulted in low R s ͑Ͻ1 ⍀ cm 2 ͒, high shunt resistance ͑60,558 ⍀ cm 2 ͒, low J o2 ͑ϳ20 nA/cm 2 ͒, and high FF ͑0.781͒. Cell efficiencies of ϳ17.4% were achieved on untextured float zone Si with 100 ⍀/ᮀ emitter by rapid firing of screen printed contacts in a lamp-heated belt furnace.Screen printed contacts are widely used for low-cost Si solar cells. Most photovoltaic ͑PV͒ manufacturers use low-sheetresistance emitters ͑Ͻ60 ⍀/ᮀ͒ because of the difficulty and challenge in achieving good screen printed contacts using high-sheetresistance emitters. Unfortunately, low-sheet-resistance emitters contribute to loss in cell performance because of heavy doping effects and high surface recombination velocity. Therefore, an attempt is made in this paper to achieve good ohmic contacts on high-sheetresistance emitters ͑100 ⍀/ᮀ͒ through improved understanding of the contact interface structure and its influence on contact quality and solar cell performance. Optimizing the inorganic constituents of the Ag paste can help achieve good-quality thick-film ohmic contacts. 1 This is particularly important when dealing with high-sheetresistance emitters. There are two possible routes to achieve goodquality ohmic contacts on lightly doped emitters. 2 The first is through self-doping techniques 3,4 and the second is via optimization of the Ag paste composition and firing cycle. 5-7 Because the diffusivity of Ag 8 is faster than that of P, 9 self-doping techniques using self-doping Ag pastes ͑Ag/P or Ag/Sb͒ probably do not prevent shunting. In this paper, the effects of Ag particle size are investigated and exploited to help in the development of Ag paste composition for high-sheet-resistance emitters using rapid firing conditions. ExperimentalIn this study, screen printed n + -p-p + solar cells ͑4 cm 2 ͒ were fabricated on single-crystal Si using carefully controlled Ag pastes and rapid firing. p-Type, 0.6 ⍀ cm, 300-m-thick ͑100͒ float-zone ͑FZ͒ substrates as well as high-sheet-resistance emitters were used for all the experiments to amplify and analyze the impact of paste ch...

The aim of this study is to understand the effect of the glass frit chemistry used in thick-film Ag pastes on the electrical performance of the silicon solar cell. The study focuses on the physical behavior of the glass frit during heat treatment as well as the resulting Ag-Si contact interface structure. We observe that the glass frit transition temperature (T g ) and softening characteristics play a critical role in the contact interface structure. The glass transition temperature also significantly influences the contact ohmicity of the thick-film metal grid. A high glass frit transition temperature generally results in thinner glass regions between the Ag bulk of the grid and the Si emitter. It was found that a glass frit (with high T g ) that crystallizes fast during the firing cycle after etching the silicon nitride and Si emitter results in smaller Ag crystallite precipitation at the contact interface. This results in smaller junction leakage current density (J o2 ) and higher open-circuit voltage (V oc ). Using high T g pastes (with the appropriate Ag powder size), greater than 0.78 fill factors and .17.4% efficiency were achieved on 4 cm 2 untextured single crystal Si solar cells with 100 V/sq emitters.

The dielectric constant and spontaneous polarization of fine-grained BaTiO(3) prepared from powder produced by metalloorganic decomposition technology were studied. The room-temperature dielectric constant of BaTiO(3) was found to increase sharply with increase in grain size, reach a maximum at about 0.4 mum, and decrease with further increase in grain size. Spontaneous polarization continuously decreased with decrease in grain size. A model is proposed to explain the grain size dependence of the dielectric constant.

The defect structure and dielectric properties of BaTiOa with 1 to 10 mol% Nd& additions were studied. The results indicated that neodymium occupies the barium site and charge compensation takes place by creation of titanium vacancies. The dependence of inverse electric susceptibility, spontaneous polarization, and specific heat on temperature for samples containing more than 2 mol% of Nd& were characteristic of a diffuse transformation resulting from a disordering of defects. The addition of Nd203 leads to a very drastic shift in the Curie temperature (T,) of BaTiO,; 3 mol% Nd& addition moves T, below room temperature.