Crystallization Regulation And Ion Migration Of Photoactive Layer In Printable Mesoscopic Perovskite Solar Cells

Metal halide perovskite materials have attracted extensive attention because of their excellent photoelectric properties and the solution-processable preparation.Having Been developing for almost ten years,the laboratory certificated power conversion efficiency(PCE)of Perovskite Solar Cells(PSCs)has reached 25.5%.However,stability and other problems still restrict the industrialization of PSCs.Printable PSCs based on mesoporous itanium dioxide/zirconium dioxide/carbon triple-layer scaffold have shown promising prospects for practical applications due to their simple fabrication process,low material cost and excellent stability.Printable PSC has successfully passed the main items of the International Institute of Electrical Engineering(IEC)qualification tests.In this paper,we study mesoporous structure and devices,focusing on the crystal regulation and ion movement of the perovskite.The content includes the following aspects:(1)A method to enhance the activity of perovskite precursor solution was developed.GBL is usually used as the solvent in printable PSCs.The perovskite solution based on GBL solvent will precipitate after a period of storage,resulting in the decrease of the precursor activity and poor repeatability of the prepared devices.Herein,we introduce Et OH into the GBL based perovskite precursor as the co-solvent,Et OH can effectively weaken the coordination interaction between GBL molecule and Pb²⁺,thus effectively inhibiting the formation of precipitation in the precursor solution.Based on Et OH modified precursor,the photovoltaic performance and device repeatability of printable PSCs were improved.After stored for more than 30 days,the PCE of the devices prepared by the precursor solution is still in the range of 14%?15.5%.(2)A method to regulate the crystallization growth of perovskite active layer was studied.The thickness of the triple-layer scaffold of the printable PSCs is more than 10?m,which makes it difficult for the precursor solution to permeate and crystallize in the mesoporous scaffold.In this section,Pb(Ac)₂ was introduced into the perovskite precursor to regulate the crystallization process of the perovskite film.Pb(Ac)₂can regulates the nucleation and growth of perovskite crystals through the formation of MAAc;in addittion,the introduction of excess Pb(Ac)₂can improve the film quality.By introducing 1%Pb(Ac)₂into the perovskite precursor solution,the photovoltaic performance of printable PSCs were improved.This work demonstrates the feasibility of regulation crystal growth kinetics through lead source additives.(3)The ion movement of perovskite in mesoporous scaffold was studied.There is an obvious ion migration phenomenon in the thin film and single crystal of organic-inorganic hybrid perovskite materials.Undoubtedly thorough insight into the ion-migration mechanism is highly desired for the development of PSCs to improve intrinsic stability.To investigate the ion migrations of perovskites in the mesoporous scaffold,we designed and fabricated lateral devices with the structure of Carbon/Zr O₂/Carbon.The morphology and composition of perovskite in mesoporous ZrO₂ were analyzed by applying constant bias voltage between Carbon electrodes,combined with in-situ microscopy and Energy Dispersion X-Ray Spectroscopy.Studies have shown that perovskite materials in inorganic mesoporous scaffold exhibit higher voltage tolerance and relatively weak ion movement.(4)The effect of bifunctional organic small molecule additives(5-AVA)on ion migration in halide perovskite was studied.Based on Kelvin Probe Force Microscopy,The Pico Cond Time-Counting Spectrometer and voltage-current measurements,we studied the ion movement dynamics and mechanism of perovskite materials in mesoporous structures.Strengthened with bifunctional organic molecular of 5-AVA at the grain boundaries,the perovskite crystal was localized on the nano scale,thus the ionic migration became reversible.The stability of mesoporous lateral device with MA-based perovskite was therefore enhanced.