Under long‐term thermal stress, the decomposition of organic‐inorganic hybrid perovskite is a big challenge to realize stable and efficient perovskite solar cells (PSCs). Thereby, it is of pivotal importance to engineer an organic hole transport layer, which is featured not only by an excellent hole conduction but also by a high glass transition temperature. Here, a solution‐processible molecular semiconductor (T5H‐EP‐BMCA) is reported. The air‐doped composite of T5H‐EP‐BMCA presents a hole density of 6.5 × 1017 cm–3, a space‐charge‐limited current hole mobility of 5.1 × 10–4 cm2 V–1 s–1, and a direct‐current electrical conductivity of 30.6 µS cm–1. Moreover, the conductive composite owns a high glass transition temperature of 165 °C, a heat‐resistant morphology, and low gas permeability coefficients. These joint attributes allow for the fabrication of 21.0%‐efficiency, 85 °C‐durable PSC by controlling the thermal decomposition of perovskite.