Direct energy gap materials, e.g. CdTe, CuInSe2, CuInGaSe2, CdSe, ZnP2 and Zn3P2, are the most interesting for thin-film solar cell applications. Among the various methods of preparation of these films, chemical bath deposition and electrodeposition deserve special attention because they have been shown to be inexpensive, low-temperature and non-polluting methods. Based on Pourbaix diagrams of CdS, CdTe, CuInSe2, CdSe, etc., drawn from basic considerations, the best parameters for their electrodeposition are deduced. Theoretical considerations on the chemical-bath deposition of CdS, CdSe and Sb2S3 are also indicated. In particular, the role of the complexing agent and of the ligands in chemical bath deposition quality is discussed, as are the uniformity and stability of the films. The photoelectrochemical, Schottky barrier and heterojunction solar cell properties based on chemically and electrochemically deposited thin films with heteropolyacids are shown. Future trends for chemically and electrochemically deposited polycrystalline thin films are addressed. Results from very recent work done in the improvement of chemically and electrochemically deposited thin films are presented. Significant results obtained on advanced CdS/CdTe, CdS/CIS and CdS/CIGS solar cells developed by industry and by laboratory groups worldwide are indicated. Emerging low cost materials or/and less environmental hazards materials which may introduce solar cells into worldwide market are considered in the conclusion.