A method (200) for fabricating patterns on the surface of a layer of a device (100), the method comprising: providing at least one layer (130, 230); adding at least one alkali metal (235) comprising Cs and/or Rb; controlling the temperature (2300) of the at least one layer, thereby forming a plurality of self-assembled, regularly spaced, parallel lines of alkali compound embossings (1300, 1305) at the surface of the layer. The method further comprises forming cavities (236, 1300) by dissolving the alkali compound embossings. The method (200) is advantageous for nanopatterning of devices (100) without using templates and for the production of high efficiency optoelectronic thin-film devices (100).