A Thiourea Competitive Crystallization Strategy for FA‐Based Perovskite Solar Cells

The solution process of perovskite solar cells may lead to widespread defects in the device, causing severe nonradiative recombination and the loss of conversion efficiency. Herein, a strategy of embedding thiourea into perovskite to manipulate the crystallization process and passivate the defects simultaneously is demonstrated. A competitive crystallization mechanism by embedding thiourea into perovskite has been proposed for the improvement of morphology and crystallinity. The defects in the device have been dramatically decreased by the strong coordination of CS bond in thiourea with the undercoordinated Pb2+. Moreover, the bilateral affinity of thiourea to the SnO2 and perovskite can enhance the interface contact by the bridging bonding, which will release the residual stress of perovskite films. As a result, the thiourea‐embedding device achieves a power conversion efficiency over 24% and shows excellent storage and illumination stabilities. Even undergoing 3768 h storage, the maximum efficiency value of unencapsulated device keeps over 94%. Furthermore, the efficiency of the optimized device maintains over 80% after 120 h continuous illumination at 60 °C. A thiourea competitive crystallization strategy is proposed to manipulate the nonequilibrium nucleation and growth in solution processible perovskite materials. The embedding thiourea has succeeded in passivating the defects, healing the lattice mismatch and relaxing the residual tensile stress. The optimized device achieves the champion efficiency over 24% simultaneously with excellent storage and illumination stabilities.