Ordered Element Distributed C 3 N Quantum Dots Manipulated Crystallization Kinetics for 2D CsPbI 3 Solar Cells with Ultra-High Performance.

Two-dimensional (2D) CsPbI 3 is developed to conquer the phase-stability problem of CsPbI 3 by introducing bulky organic cations to produce a steric hindrance effect. However, organic cations also inevitably increase the formation energy and difficulty in crystallization kinetics regulation. Such poor crystallization process modulation of 2D CsPbI 3 leads to disordered phase-arrangement, which impedes the transport of photo-generated carriers and worsens device performance. Herein, a type of C 3 N quantum dots (QDs) with ordered carbon and nitrogen atoms to manipulate the crystallization process of 2D CsPbI 3 for improving the crystallization pathway, phase-arrangement and morphology, is introduced. Combination analyses of theoretical simulation, morphology regulation and femtosecond transient absorption (fs-TA) characterization, show that the C 3 N QDs induce the formation of electron-rich regions to adsorb bulky organic cations and provide nucleation sites to realize a bi-directional crystallization process. Meanwhile, the quality of 2D CsPbI 3 film is improved with lower trap density, higher surface potential, and compact morphology. As a result, the power conversion efficiency (PCE) of the optimized device (n = 5) boosts to an ultra-high value of 15.63% with strengthened environmental stability. Moreover, the simple C 3 N QDs insertion method shows good universality to other bulky organic cations of Ruddlesden-Popper and Dion-Jacobson, providing a good modulation strategy for other optoelectronic devices.