Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press) - Provides extensive coverage of autoencoders, their architecture (encoder and decoder), latent representations, and various activation functions.
Autoencoders (UFLDL Tutorial), Andrew Ng, Jiquan Ngiam, Chuan Yu, and Yifan Hu, 2011 (Stanford University) - An excellent tutorial offering a clear, accessible explanation of autoencoders, focusing on the reconstruction process by the decoder.