The paper inside Solarcan is light sensitive and no developing is required to reveal a latent (invisible) image. When you retrieve the photograph it’s best to do so in subdued light before using a computer scanner to scan and invert the colours for your final image.
For instructions and pictures on retrieving your photograph, see our update: https://www.kickstarter.com/projects/samcornwell/the-solarcan/posts/1870674
Tl;dr? No, you don’t need chemicals.