Oriented Crystal Growth of High‐Quality Wide‐Bandgap Perovskites for Efficient Flexible Perovskite/Cu(In, Ga)Se ₂ Tandem Photovoltaics

ABSTRACT Wide‐bandgap (WBG) perovskite is a promising candidate for fabricating tandem solar cells (TSCs), which exhibit significant potential due to their capacity to surpass the Shockley‐Queisser limit. However, a key challenge lies in the poor crystallization quality of WBG perovskites, which easily induces defects and limits the device performance. Herein, a novel additive, isonicotinoyl chloride hydrochloride (INCCl) is introduced, to regulate the crystallization process and facilitate the preferential (100) orientation growth of the 1.67 eV‐WBG perovskites. Furthermore, atoms with lone electron pairs in INCCl effectively passivated uncoordinated ions and enhanced the photostability of perovskite films. As a result, the WBG perovskite solar cells (PSCs) demonstrated a high champion power conversion efficiency (PCE) of 24.01%, and retained over 90% of the initial PCE after ≈1380 h of maximum power point (MPP) tracking. In addition, the INCCl‐modified flexible perovskite/Cu(In, Ga)Se ₂ (CIGS) TSCs delivered a champion PCE of 25.02% on an industry‐grade flexible CIGS substrate, along with superior bending stability and operational durability. This work provides an effective additive strategy for preparing high‐quality WBG perovskite films, demonstrating significant potential for advancing the tandem applications.