Infiltrated 2D/3D Heterojunction with Tunable Electric Field Landscape for Robust Inverted Perovskite Solar Cells with over 24% Efficiency.

In inverted perovskite solar cells, conventional planar 2D/3D perovskite heterojunctions typically exhibit a type-II band alignment, where the electric field tends to drive the electron motion in the opposite direction to the direction of electron transfer. Here, a 2D/3D gradient heterojunction is developed by allowing the 2D perovskite to infiltrate the 3D perovskite surface along the grain boundaries using the interaction between the organic cation of the 2D perovskite and the pseudohalogen thiocyanate ion (SCN-), which has the ability to diffuse downward. The infiltrated 2D perovskite not only fills the gaps of grain boundaries with improved structural stability, but it also reconstructs the original landscape of the electric field toward the n-doped surface to enable more rapid electron transfer and weaken the adverse type-II band alignment effect. Since 2D perovskite seals the GBs, the nonvolatile SCN- can accumulate at the top and bottom dual interfaces, releasing residual stress and significantly inhibiting nonradiative recombination. The device exhibits an excellent efficiency of 24.76% (certified 24.29%) and long-term stability that is >90% of the original PCE value after 800 h of heating at 85 °C or in high humidity (≈65%).

Efficient Charge Transport in Inverted Perovskite Solar Cells via 2D/3D Ferroelectric Heterojunction.

While the 2D/3D heterojunction is an effective method to improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs), carriers are often confined in the quantum wells (QWs) due to the unique structure of 2D perovskite, which makes the charge transport along the out-of-plane direction difficult. Here, a 2D/3D ferroelectric heterojunction formed by 4,4-difluoropiperidine hydrochloride (2FPD) in inverted PSCs is reported. The enriched 2D perovskite (2FPD)2PbI4 layer with n = 1 on the perovskite surface exhibits ferroelectric response and has oriented dipoles along the out-of-plane direction. The ferroelectricity of the oriented dipole layer facilitates the enhancement of the built-in electric field (1.06 V) and the delay of the cooling process of hot carriers, reflected in the high carrier temperature (above 1400 K) and the prolonged photobleach recovery time (139.85 fs, measured at bandgap), improving the out-of-plane conductivity. In addition, the alignment of energy levels is optimized and exciton binding energy (32.8 meV) is reduced by changing the dielectric environment of the surface. Finally, the 2FPD-treated PSCs achieve a PCE of 24.82% (certified: 24.38%) with the synergistic effect of ferroelectricity and defect passivation, while maintaining over 90% of their initial efficiency after 1000 h of maximum power point tracking.

Minimizing Interfacial Energy Loss and Volatilization of Formamidinium via Polymer-Assisted D-A supramolecular Self-Assembly Interface for Inverted Perovskite Solar Cells with 25.78% Efficiency.

2D perovskite passivation strategies effectively reduce defect-assisted carrier nonradiative recombination losses on the perovskite surface. Nonetheless, severe energy losses are causing by carrier thermalization, interfacial nonradiative recombination, and conduction band offset still persist at heterojunction perovskite/PCBM interfaces, which limits further performance enhancement of inverted heterojunction PSCs. Here, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (5FTPP) is introduced between 3D/2D perovskite heterojunction and PCBM. Compared to tetraphenylporphyrin without electron-withdrawing fluoro-substituents, 5FTPP can self-assemble with PCBM at interface into donor-acceptor (D-A) complex with stronger supramolecular interaction and lower energy transfer losses. This rapid energy transfer from donor (5FTPP) to acceptor (PCBM) within femtosecond scale is demonstrated to enlarge hot carrier extraction rates and ranges, reducing thermalization losses. Furthermore, the incorporation of polystyrene derivative (PD) reinforces D-A interaction by inhibiting self-π-π stacking of 5FTPP, while fine-tuning conduction band offset and suppressing interfacial nonradiative recombination via Schottky barrier, dipole, and n-doping. Notably, the multidentate anchoring of PD-5FTPP with FA+, Pb2+, and I- mitigates the adverse effects of FA+ volatilization during thermal stress. Ultimately, devices with PD-5FTPP achieve a power conversion efficiency of 25.78% (certified: 25.36%), maintaining over 90% of initial efficiency after 1000 h of continuous illumination at the maximum power point (65 °C) under ISOS-L-2 protocol.