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The recent progress towards high-efficiency thin-film polycrystalline solar cells is examined in this paper together with a brief history of their development. On three materials of contempory is focused the interest for such devices: polycrystalline Si, CuInSe2 and its alloys, and CdTe. Although there has often been an implicit assumption that thin-films devices required a compromise of lower efficiency than their single, or bulk polycrystalline competitors, for the first time it is seen that polycrystalline thin-film solar cells can reveal these devices. In dispelling this myth, the elements are examined that have contributed to the progress in each area. More basic technical issue remain to be solved. Our basic understanding of the mechanism of film growth for CuInSe2 needs further work to be generally accepted: clearly more must be done to extend the model in a detailed fashion to the alloys, both Ga- and S-substituted. One might speculate that the more rapid commercialization of CdTe has been due to chance but to the many choices available for the deposition of high-quality films of that material. Hence, it may be important to the commercialization of CuInSe2 to develop straight forward alternate means of depositing the device-quality alloy films. It is unknown if the present process, which requires high-temperature substrates and sources, will allow low-cost, large-area manufacturing. Alternative methods, such as sputtering, spray deposition, and electrodeposition should be pursued with the goal of obtaining the same high-performance devices, keeping in mind the mechanism of film formation of evaporated films. A less serious problem - the use of a CdS n-type heterojunction partner - also needs to be addressed to simplify processing. Clearly, long-term research subjects such as substrate devices and the use of flexible substrates will broaden the range of CuInSe2-based products.