In situ molecular compensation in wide-bandgap perovskites for efficient all-perovskite tandem solar cells

Substantial VOC loss and halide segregation in wide-bandgap (WBG) perovskite sub-cells pose significant challenges to the advancement of all-perovskite tandem solar cells (APTSCs). One of the most impactful developments addressing this issue is the application of hole-selective self-assembled monolayers (SAMs), which has led to significant progress in APTSC technology. However, SAMs with poor resistance to polar solvents are inevitably delaminated from substrates during perovskite precursor coating, presenting a major challenge in achieving complete SAM coverage. This leads to derivatization issues, such as defective perovskite formation and considerable interfacial energy loss. Here, we introduced an in situ molecular compensation strategy to address the inherent limitation of SAMs in WBG perovskites by incorporating 5-ammonium valeric acid iodide (5-AVAI). The high-dipole 5-AVAI spontaneously accumulated at the buried interface to compensate for SAM-deficient sites during WBG perovskite deposition, effectively minimizing interfacial energy loss. Simultaneously, the amphoteric 5-AVAI, containing both amino and carboxyl groups, could compensate defects at grain boundaries for solid passivation. Consequently, a champion efficiency of 20.23% with a record VOC of 1.376 V was achieved in WBG devices, enabling an overall efficiency of 28.9% for the APTSCs. Encouragingly, the tandem devices showed good operational stability, retaining 87.3% of their initial efficiency after 800 h of continuous tracking.