Ni nanobelts induced enhancement of hole transport and collection for high efficiency and ambient stable mesoscopic perovskite solar cells

Abstract

Highly efficient photo-generated carrier transfer is one of the key factors in determining the performance of organic–inorganic hybrid perovskite solar cells (PSCs). Here, we demonstrate a strategy for improved hole transfer and collection by employing a composite hole transporting material (HTM) consisting of free standing Ni nanobelts dispersed in the widely used 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). It is found that power conversion efficiency (PCE) and ambient stability of mesoscopic PSCs have been improved. To be more specific, in order to prevent significant charge recombination induced by direct contact of the metal Ni with a perovskite absorber, a spiro-OMeTAD intermediate layer was spin-coated on the CH₃NH₃PbI₃ layer prior to the sequentially deposited layers of Ni nanobelts and spiro-OMeTAD. With this architecture, the optimized PSC achieved a champion PCE of 16.18% with a short-circuit current density (J_sc) of 21.64 mA cm⁻², an open-circuit voltage (V_oc) of 1.02 V, and a fill factor (FF) of 73.3% under reverse scanning. Despite the small J–V hysteresis, a higher stabilized efficiency up to 14.47% near the maximum power point could be reached for the device fabricated with 1.8 mg mL⁻¹ Ni nanobelts compared with the pristine one (12.05%). However in the presence of highly hygroscopic lithium-bis(trifluoromethane) sulfonimide (Li-TFSI), PSCs in conjunction with Ni nanobelts present an impressively favorable ambient stability with an observed PCE retention rate of over 85% after 4-week storage with exposure to ambient air without any encapsulation.