Tailoring crystallization and oriented growth through crosslinking molecules toward efficient and stable CsPbI₂Br perovskite solar cells

Wide-bandgap all-inorganic CsPbI₂Br perovskite is a promising top-cell absorber for tandem photovoltaic devices, but suffers from rapid, disordered crystallization and defect-induced instability. This study employs a crosslinking Lewis base molecule, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), to regulate the crystallization and oriented growth of CsPbI₂Br. In the precursor, the sulfonate group (-SO₃⁻) of AMPS coordinates with Pb²⁺, forming larger colloids that lower the nucleation barrier and promote the formation of dense films. During annealing, both the -SO₃⁻ and carbonyl (C=O) groups coordinate with Pb²⁺, leading to the horizontal adsorption of AMPS on the (200) crystal plane. This significantly lowers the surface formation energy of the (200) crystal plane, promoting preferential crystal growth along the (200) orientation. Meanwhile, the in-situ polymerization of AMPS forms a crosslinked network, which, combined with the improved crystallinity, effectively relieves the residual tensile strain. Ultimately, n-i-p devices fabricated using AMPS-treated CsPbI₂Br achieve a power conversion efficiency (PCE) of 17.28%, with an open-circuit voltage (V_OC) of 1.367 V, a short-circuit current density (J_SC) of 15.83 mA·cm⁻², and a fill factor (FF) of 79.86%. In addition, the devices retain 90% of their initial efficiency after 660 h at 20–30% relative humidity (RH), and 75% after 500 h of continuous maximum power point (MPP) tracking.