peri-Fused polyaromatic molecular contacts for perovskite solar cells.

Molecule-based selective contacts have become a crucial component to ensure high-efficiency inverted perovskite solar cells1-5. These molecules always consist of a conjugated core with heteroatom substitution to render the desirable carrier-transport capability6-9. So far, the design of successful conjugation cores has been limited to two N-substituted π-conjugated structures, carbazole and triphenylamine, with molecular optimization evolving around their derivatives2,5,10-12. However, further improvement of the device longevity has been hampered by the concomitant limitations of the molecular stability induced by such heteroatom-substituted structures13,14. A more robust molecular contact without sacrificing the electronic properties is in urgent demand, but remains a challenge. Here we report a peri-fused polyaromatic core structure without heteroatom substitution that yields superior carrier transport and selectivity over conventional heteroatom-substituted core structures. This core structure produced a relatively chemically inert and structurally rigid molecular contact, which considerably improved the performance of perovskite solar cells in terms of both efficiency and durability. The champion device showed an efficiency up to 26.1% with greatly improved longevity under different accelerated-ageing tests.

Rising from the Ashes: Gaseous Therapy for Robust and Large-Area Perovskite Solar Cells.

Scalable fabrication of perovskite solar cells (PSCs) with high reliability is one of the most pivotal concerns that must be addressed before they get into the photovoltaic (PV) market. Scaling large-area high-quality perovskite films is of great importance in this process. Here, gaseous therapy has been proposed for the post-treatment of perovskite films with high scalability and low cost. An inspiring evolvement from poor perovskite films to high quality ones is demonstrated under a joint treatment of methylamine gas and hot solvent vapors. The perovskite films are completely reconstructed and repaired regardless of the morphology of the original films. As a consequence, small-area (0.09 cm2) and large-area (4 cm2) PSCs based on the healed MAPbI3 films can afford J-V scanned efficiencies of 19.2 and 16.5% under a reverse sweep, respectively. Furthermore, stabilized power outputs of 18.5 and 15.2% are obtained from the small one and large one under continuous maximum power point tracking.

Effects of Annealing Time on Triple Cation Perovskite Films and Their Solar Cells.

Cesium (Cs) contained triple-cation and mixed halide perovskite (CsFAMA) is broadly employed as light absorption layers for efficient and stable perovskite solar cells (PSCs) fabrication with high reproducibility. On the other hand, thermal annealing is a universal post-treatment method for perovskite films preparation. Moreover, thermal management highly depends on perovskite materials. However, no specialized study has been reported on CsFAMA perovskite to date. Herein, we have systematically investigated the influence of thermal annealing and annealing time on CsFAMA films and their solar cells. We demonstrated that heating time of 45 or 60 min at 100 °C is desirable. More interestingly, we found that the unannealed CsFAMA films exhibit ultrahigh photoluminescence (PL) intensities, much stronger than that of annealed films. Note that PL intensities gradually weaken as a function of annealing time. In particular, the PL intensities of fresh films (after antisolvent dripping) are at least 200 times higher than that of 60 min annealed films. To our knowledge, it is the first time to report this PL behavior. We speculate that it is due to quantum confinement effect of perovskite crystal nuclei and "cage effect" of DMSO intermediates in the fresh films. To this point, the unannealed CsFAMA films may have great potential in PL emission applications.