Cross-linking polymerization boosts the performance of perovskite solar cells: from material design to performance regulation

Abstract

Perovskite polycrystalline films with massive grain boundaries (GBs) lead to high defect densities as well as poor environmental stability. Polymer additives provide an effective insight to solve these problems. However, certain polymers originating from ex situ polymerization have poor solubility and adversely affect perovskite nucleation. Comparatively speaking, in situ cross-linking polymerization shows more obvious superiority in the nucleation and crystal growth of perovskite films. However, no literature systematically reports the research progress and mechanism of the in situ polymerization reaction. In this review, we analyze comprehensively the characteristics of in situ polymerization and ex situ polymerization. Then, the performance regulation and underlying mechanisms of in situ polymerization are elaborated, including crystallization regulation, defect passivation, ion migration suppression, flexibility enhancement, self-healing ability, and stability improvement. Meanwhile, we overview the effects of an in situ polymerization reaction within the perovskite lattice: enhancing the lattice rigidity, flexibility, stability, etc. Furthermore, we highlight the advances in in situ polymerization in the charge transport layers (CTLs). Finally, we outline the challenges and opportunities of in situ cross-linking polymerization.