How to render in single pages ($this->render)

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Hi everybody!
I have a little problem. In my controller, located in "application/controllers/newsletter.php", I have the command "$this->render('')".
When using the command "$this->render()" it searches for the file to include in the directory "concrete/single_pages/my_folder" and not in the directory "application/single_pages/my_folder".
Is it possible to tell concrete5 to search for the file in the application directory.
I've tried it with "$this->render('application/single_pages/my_folder')" but the result was the the file was searched in "concrete/single_pages/application/single_pages/my_folder".

Has anybody an idea or hint?

Thanks

Chris