Inverted perovskite solar cells with air stable diketopyrrolopyrrole-based electron transport layer

One of the possible causes of degradation of perovskite solar cells is the instability of the electron transporting layer. In this regard, design of air stable electron transport organic semiconductors, compatible with perovskite energy levels presents challenges due to inherent vulnerability to traps, presumably originating due to water and/or oxygen. In this work, we demonstrate air stability of diketopyrrolopyrrole-based molecule (TDPP-CN₄) at ambient conditions and its application as electron transporting layer (ETL) in perovskite solar cells. We investigated electron mobility and air stability of TDPP-CN₄ by fabricating top-gate bottom-contact (TG-BC) thin film transistors and compared with PCBM at ambient conditions. Both TDPP-CN₄ and PCBM exhibit electron transport properties with mobility of 0.13 cm² V⁻¹ s⁻¹ and 0.03 cm² V⁻¹ s⁻¹ respectively. However, we found remarkable air stability of the TDPP-CN₄ in the OFET measurements under ambient conditions. These excellent properties of TDPP-CN₄ render them as potential ETL layer in inverted planar heterojunction perovskite solar cells. Our preliminary device studies show remarkable short-circuit current (J_sc) ∼ 17.4 mA/cm² with moderate open-circuit voltage (V_oc) of 0.50 V. These results suggest that the electron mobility and air-stability of diketopyrrolopyrrole-based molecule hold a promise as ETL in perovskite solar cells at ambient conditions.