The low cost and scalability advantages of printable mesoscopic perovskite solar cells (p-MPSCs) are impaired by the issue of limited power conversion efficiency (PCE). Herein, the PCE of p-MPSCs is improved by introducing the polymer additive polyacrylonitrile (PAN) into the formamidinium (FA)-based perovskite for crystallization and defect modulation. PAN forms hydrogen bond and coordination bond with halide perovskite through its C≡N group. Such interactions improve the crystallization and filling of FA-based perovskite in the mesoscopic scaffold and bring a long carrier lifetime by passivating defects. The synergy improves the PCE of p-MPSCs from 16.80% to 18.33%. Meanwhile, the hydrophobic nature of PAN enhances the device's resistance against moisture. This work demonstrates that the polymer additive is a promising choice for breaking the PCE limit of p-MPSCs.
One of the key issues of lead-free halide double perovskite nanocrystals (DPNCs) is their low photoluminescence quantum yields (PLQYs), and the PLQYs of nondoped pristine DPNCs are currently below 2%, though they can be enhanced via strategies such as ion doping or surface passivation. Herein, we report an organic–inorganic hybrid approach to significantly increase the PLQYs of nondoped pristine DPNCs. With Cs2NaBiCl6 NCs as the model, we selected methylammonium (MA+) and formamidine (FA+) as organic A-site ions and for the first time successfully synthesized the organic–inorganic hybrid in-direct bandgap DPNCs, e.g., MA2NaBiCl6 and FA2NaBiCl6. The PLQYs of the prepared Cs2NaBiCl6, MA2NaBiCl6, and FA2NaBiCl6 are 1.9%, 6.2%, and 15.4%, respectively. The enhancement of PLQYs can be due to the lattice distortion on using the unsymmetric rod-like MA+ and V-like FA+ to replace the symmetric Cs+, which yields faster charge transfer, enhanced excitation, and reduced nonradiative recombination, which are combined to make the self-trapped excited state brighter with significantly enhanced PLQYs. Overall, our results clearly demonstrate that the organic–inorganic hybrid strategy is an effective way to tune the lattice distortion and significantly enhance the emission of nondoped DPNCs, which will open doors for designing functional optoelectronic materials.
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