RESUMEN
Perovskite solar cells (PSCs) with n-i-p structures often utilize an organic 2,2',7,7'-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9'-spirobifluorene (spiro-OMeTAD) along with additives of lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) and tert-butylpyridine as the hole transporting layer (HTL). However, the HTL lacks stability in ambient air, and numerous defects are often present on the perovskite surface, which is not conducive to a stable and efficient PSC. Therefore, constructive strategies that simultaneously stabilize spiro-OMeTAD and passivate the perovskite surface are required. In this work, it is demonstrated that a novel ionic liquid of dimethylammonium bis(trifluoromethanesulfonyl)imide (DMATFSI) could act as a bifunctional HTL modulator in n-i-p PSCs. The addition of DMATFSI into spiro-OMeTAD can effectively stabilize the oxidized spiro-OMeTAD+ cation radicals through the formation of spiro-OMeTAD+ TFSI- because of the excellent charge delocalization of the conjugated CF3 SO2 - moiety within TFSI- . In addition, DMA+ cations could move toward the perovskite from the HTL, resulting in the passivation of defects at the perovskite surface. Accordingly, a power conversion efficiency of 23.22% is achieved for PSCs with DMATFSI and LiTFSI co-doped spiro-OMeTAD. Moreover, benefiting from the improved ion migration barrier and hydrophobicity of the HTL, still retained nearly 80% of their initial power conversion efficiency after 36 days of exposure to ambient air.
RESUMEN
Regardless of the impressive progress that perovskite solar cells (PSCs) have achieved, especially considering their power conversion efficiency (PCE) over 25%, traditional PSCs still contend with an inherent instability with exposure to humidity, which remains as a critical issue for the realization of commercial production. Herein, we proposed an effective pathway to relieve the instability of PSCs without sacrificing efficiency by introducing a 2D phase at the surface of the 3D perovskite film, based on a novel organic cyclohexylmethylammonium iodide (CMAI). The self-assembled thin 2D capping layer atop the 3D perovskite layer can not only reduce the ionic defects, but also serve as a protective barrier against moisture. Consequently, the champion device incorporating 2D perovskite capping layers delivered an open-circuit voltage (Voc) of 1.19 V, which contributes to an impressive PCE of 22.06% on account of the improved charge extraction and decreased non-radiative recombination. More importantly, an excellent long-term stability along with mitigated hysteresis was observed for the modified devices as a result of the suppressed ion migration and high humidity resistance of the 2D perovskite film. Our finding provides a comprehensive approach for simultaneously enhancing the efficiency and stability of PSCs through dimension engineering utilizing CMA-based 2D perovskite materials.
