DE3122992C2 - - Google Patents

Description

The invention relates to a method for producing a unsubstituted polysilane with the composition

where x 10 and n is 1 to 2.

Unsubstituted polysilanes are potential precursors for hydrogenated amorphous silicon films. These films have properties like photoconductivity and can be applied in xerography, for image intensifiers and photoelectric Devices including solar cells, the films of such can include amorphous silicon on substrates. Such Solar cells promise the important advantage of moderate Costs for large areas with good effectiveness.

Various syntheses for polysilanes are known. Some go from compounds such as (SiBr₂) _x or Si₅H₁₀, which are not commercially available, which increases the number of steps to be performed. Another method is based on SiHBr₃, which should be explosive as it is generally manufactured. A typical known synthesis given by Stock and Zaidler in Chemical Reports Vol. 56 (1923), p. 986 proceeds as follows:

SiHCl₃ + Na → (SiH) _x .

However, since the sodium is in the form of an amalgam, the  Separation of the product difficult.

Another typical known method, that of stock and Somieski in Chemical Reports, Vol. 56 (1923), p. 247 as follows:

SiH₃Cl + Na → (SiH₂) _x .

However, the yield is low (theoretical maximum 2/3 x) and the main product is monosilane, which can explode on contact with air.

Another method that is easy to use in a variety of ways substituted ring compounds is given by Matsumura, Brough and West in JCS Chemical Communications 1978 pp. 1092 and proceeds as follows:

The object of the present invention is a simple method to develop an unsubstituted polysilane that the does not have the above-mentioned disadvantages.

This object is achieved by the one stated in the main claim Method.

The molar ratio of lithium to SiH _m Cl _{4- m} should be greater than (4- m) : 1 and preferably 2.5 (4- m) : 1 (ie 5: 1 for dichlorosilane). The weight ratio of lithium to the liquid can e.g. B. 1:90; m is preferably 2.

The inert liquid is preferably sufficient Amount available to dissolve all of the resulting LiCl. A preferred liquid is tetrahydrofuran.

Example 1

0.3 g (0.04 mol) of lithium was carefully dried in 30 cm³ (27 g) and degassed tetrahydrofuran. These Suspension was made in the absence of moisture and air gaseous dichlorosilane SiH₂Cl₂ (0.20 g; 0.002 mol) initial partial pressure implemented at room temperature 532 mbar.

After 18 hours, an orange air sensitive one fell Powder and was made by the suspension is removed within no more than 24 hours, to further implement the powder as little as possible to keep. The powder sank to the bottom while the lithium sank stayed on the surface. That made the separation easier. The Tetrahydrofuran showed when subsequently exposed to the air no reactivity and this shows that silane compounds, which would be soluble in tetrahydrofuran, not in were formed to a significant extent. That at the Reaction formed lithium chloride, which is in tetrahydrofuran could be precipitated from this by adding hexane will.

The orange powder showed bands in the IR spectrum that were analogous to those of thin films of hydrogenated amorphous silicon made by glow discharge.

The powder is therefore used as an unsubstituted polysilane composition

viewed, where n is approximately 2 and x appeared to be at least 20.

Example 2

0.3 g (0.04 mol) of lithium was carefully diluted in 30 cm³ (27 g) dried and degassed tetrahydrofuran dissolved. These Solution was made in the absence of moisture and air dry trichlorosilane SiHCl₃ (0.27 g; 0.002 mol) Room temperature implemented. The trichlorosilane appeared with that Tetrahydrofuran to be miscible.

After 18 hours, a brown air-sensitive, solid powder that was removed from the suspension in no more than 24 hours, in order to keep a further reaction of the powder as low as possible. The powder sank to the bottom in the liquid while that Lithium rather swam on the surface. That made it easier Separation. The tetrahydrofuran showed no reactivity, if it was subsequently exposed to the air. It shows that Ring compounds that would be soluble in tetrahydrofuran are not had arisen to a significant degree.

The brown powder was considered unsubstituted due to the IR spectrum Polysilane of the composition

where n is considered approximately 1. Based on other research, x appeared to be 20 or larger.

Claims (1)

Process for the preparation of an unsubstituted polysilane of the composition where x 10 and n is 1 to 2, by reacting SiH _m Cl _{4- m} , where m is 1 or 2, with an alkali metal, characterized in that lithium is used as the alkali metal and the reaction in a suspension in a liquid, which is inert to the reagents and the product and in which the polysilane is insoluble and the resulting LiCl is soluble.