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Hybrid organic-inorganic halide perovskite solar cells (PSCs) have achieved intriguingly high photoelectric conversion efficiencies (PCEs), but their operational stability is still not satisfactory owing to their vulnerability to moisture and heat. Herein, we report the introduction of pseudohalide thiocyanate ions and potassium dopants into formamidinium lead triiodide (FAPbI3) to obtain a new class of pseudohalide-substituted lead halide perovskites FAPb(SCN)2I that can be prepared in ambient air and exhibit broad-range light absorption. Through the introduction of K+-cation doping, hole-conductor-free PSCs based on a FA0.98K0.02Pb(SCN)2I perovskite light absorber and a low-cost, screen-printable carbon-based counter electrode exhibited a PCE of 13.39%. Importantly, the FA0.98K0.02Pb(SCN)2I-based hole-conductor-free PSCs exhibited an 88% PCE retention even after continuous heating at 100 °C for 1020 h, indicating excellent thermal stability. This study suggests that the compositional engineering of non-iodine X-site pseudohalide anion substitution and A-site cation doping hold great promise for improving the stability of PSCs.