Ultra‐Sensitive Bulk Piezophotovoltaic Effect in NaBa(P,Bi) Alloy Under Topological Phase Transition

Abstract The bulk photovoltaic effect, with ultra‐sensitive control under ambient piezo response, plays a significant role in many modern optoelectronic applications. However, functional bulk photovoltaic materials with high piezo sensitivity are rare, and discovering them is a great challenge. This article proposes a practical design scheme to achieve an ultra‐sensitive bulk piezophotovoltaic effect (BPPVE) in a single‐valley topological alloy material system. The BPPVE is accomplished by reversing the giant shift current in an alloy material that exhibits piezo‐sensitive topological band inversion, as predicted in the acentric single‐valley NaBa(P,Bi) alloy system. First‐principles calculations confirm that the shift current in NaBaP_1‐xBi_x has high directional and magnitude sensitivity (−5000 to 400 µA V⁻²) in a rather low‐stress region (<0.5 GPa) near the critical alloy concentration (x ∼ 0.48), along with a remarkable topological phase transition. Notably, the stress‐induced bulk photovoltaic effect in NaBa(P,Bi) is much more sensitive than in other existing bulk photovoltaic materials. The outcomes demonstrate an outstanding BPPVE with ultra‐high piezo sensitivity for the first time in topological alloy systems.