Catalysts, chemical stability, and light harvesting are three major challenges in developing high performance photoelectrochemical water-splitting devices. Here we report the significant improvement of using bifacially designed schemes for achieving an ultrahigh solar to hydrogen efficiency of 18.22% with ultrafast hydrogen production rate and excellent chemical stability up to 370 hr. By deposition with appropriate catalyst (Pt) thickness, we have successfully balanced the trade-off among catalytic reaction, chemical protection, and light harvesting properties. In addition, the well-distributed catalytic and light harvesting sites provided by Si bifacial photoelectrochemical cells exhibit significantly higher omnidirectional hydrogen production capability as compared to conventional single-sided devices. Light-intensity dependent characterization is further demonstrated for realizing the bifacial photoelectrochemical cell in practical applications. The well-controlled, high efficiency, and chemically stable photoelectrochemical cell demonstrated herein can provide an important advance towards the development of next-generation renewable energy devices.