Researchers from Nankai University, Ningbo University and Chinese Academy of Sciences have developed a molecular interface engineering strategy that directs vertical crystallization in Dion-Jacobson (DJ) perovskite solar cells, significantly improving both efficiency and operational stability.
Two-dimensional perovskites are inherently more stable than their 3D counterparts, but their photovoltaic performance is often limited by inefficient charge transport, largely due to unfavorable crystal orientation. To address this, the team introduced dual-anchoring organic acids - croconic acid (CA) and squaric acid (SA) - as functional interlayers between the NiOx hole transport layer and a thieno[3,2-b]thiophene-2,5-diyldimethanaminium (TTDMA)-based DJ perovskite with a nominal layer number of n=4.
Both CA and SA exhibit strong chemical interactions with the NiOx surface and the overlying perovskite. However, their structural behavior differs markedly. CA forms a twisted, disordered interfacial layer due to multivalent coordination with NiOx, which limits its ability to guide crystal growth. In contrast, SA adopts an ordered vertical configuration through bidentate coordination, creating a well-defined molecular template that directs perovskite nucleation and promotes vertically aligned crystal growth.
This templating effect leads to highly crystalline (TTDMA)(MA0.4FA0.6)n−1PbnI3n+1 films with improved vertical orientation. At the same time, the SA interlayer plays multiple functional roles: it passivates interfacial defects, relieves lattice strain, improves energy level alignment, and suppresses the oxidation of iodide ions (I−) induced by Ni3+ species in the NiOx layer. These combined effects enhance charge transport and reduce non-radiative recombination losses.
As a result, solar cells incorporating the SA-modified interface achieved a champion power conversion efficiency (PCE) of 22.03%, with a certified value of 21.42%, alongside markedly improved operational stability. This represents a record performance for DJ perovskite solar cells.
Importantly, the strategy was also shown to be generalizable. The same vertical crystallization control was demonstrated in Ruddlesden-Popper (RP) perovskites using thieno[3,2-b]thiophen-2-ylmethanaminium (TTMA) as the spacer, confirming the broader applicability of this molecular interface design.
Overall, this work highlights how molecular-scale control at buried interfaces can simultaneously regulate crystal growth, reduce interfacial degradation pathways, and unlock higher efficiencies in layered perovskite photovoltaics.
