Long carrier diffusion length is important for optoelectronic devices that require large electrode spacing or thick active layers. Formamidinium lead triiodide (FAPbI₃) perovskite is a promising candidate with ultra-long carrier diffusion length, but the existence of internal tensile strain and formation of ion vacancies make its photoactive black phase thermodynamically unstable. Herein, phase-stable FAPbI₃-based single crystals with negligible absorption loss are achieved by synergy of iodide immobilization and compressive strain. Incorporation of guanidinium (GA⁺) cations strengthens the interaction with the inorganic framework and suppresses the formation of iodide ion vacancies. Besides, the interface compressive strain introduced from the indium tin oxide (ITO) substrate counteracts the lattice tensile strain. The as-grown GA_0.015FA_0.985PbI₃ single crystals exhibit no phase transition after storage in air for 2,000 h. Moreover, the GA_0.015FA_0.985PbI₃ single crystals exhibit ultra-long electron carrier diffusion length of about 600 μm, which is a record value for perovskite materials and only half of silicon single crystals.

长载流子扩散长度对于需要大电极间距或厚有源层的光电器件非常重要。三碘化甲脒铅（FAPbI ₃ ）钙钛矿是一种具有超长载流子扩散长度的有前途的候选材料，但内部拉伸应变的存在和离子空位的形成使其光敏黑相热力学不稳定。在此，通过碘化物固定和压缩应变的协同作用实现了吸收损失可忽略不计的相稳定的FAPbI _{3基单晶。}胍 (GA ⁺ ) 阳离子的掺入增强了与无机骨架的相互作用并抑制了碘离子空位的形成。此外，从氧化铟锡（ITO）基板引入的界面压缩应变抵消了晶格拉伸应变。生长的 GA _0.015 FA _0.985 PbI ₃单晶在空气中储存 2,000 小时后没有表现出相变。此外，GA _0.015 FA _0.985 PbI ₃单晶表现出约600 μm的超长电子载流子扩散长度，这是钙钛矿材料的记录值，仅为硅单晶的一半。