Traditional solar thermophotovoltaics (STPV) rely on intermediate layers to convert the broadband sunlight to the desired emission spectrum for photovoltaic cells. However, these intermediate layers suffer from substantial photon loss caused by the back emission from the layer towards the sun. Such photon loss is inevitable due to the reciprocity of the system. Here we propose an STPV system that utilizes an intermediate layer with nonreciprocal radiative properties. Such nonreciprocal property can help the intermediate layer to substantially suppress its back emission to the sun and direct the sunlight towards the cell. We show that this nonreciprocal STPV system can approach the Landsberg efficiency 93.3% in the ideal case, which is significantly higher than traditional STPV that is subject to the blackbody limit of 85.4%. The adaption of the nonreciprocal intermediate layer also brings a significant improvement on the efficiency in practical STPV systems with single-junction photovoltaic cells, offering a new pathway to achieve record-breaking performance in solar energy harvesting systems.