All foreign nationals entering and staying in Germany must be in possession of a valid entry and stay visa, unless you are exempt from this requirement.
Upon request, the conference organizers could provide an official letter of invitation in order to facilitate your visa application. This invitation letter does not imply any commitment from the Organizing Committee to provide any kind of financial contribution.
The request should be made by e-mail and must include:
First name (as shown in passport)
Last name (as shown in passport)
Country of citizenship
Affiliation (supported by a document certifying it)