Optical absorption of rectangular a-Si/c-Si solar cells is investigated. Each nanowire consists of a thin layer of a-Si, which surrounded by c-Si layers. The proposed structure has a very simple geometry compared with other nanowire solar cells, while its absorption rate is comparable to very complex structures. Periodic, semiperiodic, and multiple rectangular nanowires are used to achieve broadband absorption. In order to maximize the short-circuit current density of the proposed nanowire solar cells, particle swarm optimization algorithm has been performed. Irregularities have been observed to be one of the ways of absorbing broadband.