Aligned and Graded Type-II Ruddlesden-Popper Perovskite Films for Efficient Solar Cells

Recently, Ruddlesden-Popper perovskites (RPPs) have attracted increasing interests due to their promising stability. However, the efficiency of solar cells based on RPPs is much lower than that based on 3D perovskites, mainly attributed to their poor charge transport. Herein, a simple yet universal method for controlling the quality of RPP films by a synergistic effect of two additives in the precursor solution is presented. RPP films achieved by this method show (a) high quality with uniform morphology, enhanced crystallinity, and reduced density of sub-bandgap states, (b) vertically oriented perovskite frameworks that facilitate efficient charge transport, and (c) type-II band alignment that favors self-driven charge separation. Consequently, a hysteresis-free RPP solar cell with a power conversion efficiency exceeding 12%, which is much higher than that of the control device (1.5%), is achieved. The findings will spur new developments in the fabrication of high-quality, aligned, and graded RPP films essential for realizing efficient and stable perovskite solar cells.
Funding Agencies|Research Grants Council of the Hong Kong Special Administrative Region, China [11304115]; National Natural Science Foundation of China [51473138]; Joint NTU-LiU Ph.D. programme on Materials and Nanoscience; Swedish Research Council VR [330-2014-6433]; European Commission Marie Sklodowska-Curie action [INCA 600398, 691210]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Nanyang Technological University [M4080514]; Ministry of Education Academic Research Fund Tier 1 grants [RG101/15, RG173/16]; Ministry of Education Academic Research Fund Tier 2 grants [MOE2014-T2-1-044, MOE2015-T2-2-015, MOE2016-T2-1-034]; Singapore National Research Foundation through the Competitive Research Program [NRF-CRP14-2014]; Marie Sklodowska-Curie Fellowship [2016-02051]