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We characterize heterojunction solar cells made from single-crystal silicon films grown heteroepitaxially using hot-wire chemical vapor deposition (HWCVD). Heteroepitaxy-induced dislocations limit the cell performance, providing a unique platform to study the device physics of thin crystal Si heterojunction solar cells. Hydrogen passivation of these dislocations enables an open-circuit voltage VOC close to 580 mV. However, dislocations are partially active, even after passivation. Using standard characterization methods, we compare the performance of heteroepitaxial absorbers with homoepitaxial absorbers that are free of dislocations. Heteroepitaxial cells have a smaller diffusion length and a larger ideality factor, indicating stronger recombination, which leads to inefficient current collection and a lower VOC than homoepitaxial cells. Modeling indicates that the recombination in the inversion layer of heterojunction cells made from defective absorbers is comparable with the overall recombination in the bulk. Temperature-dependent VOC measurements point to significant recombination at the interface that is attributable to the presence of dislocations.