Green Solvent Processing And Optoelectronic Properties Of Perovskite Films

Organic-inorganic hybrid perovskite solar cells(PSCs)have attracted worldwide attention due to their excellent photoelectric properties.However,most of the reported high-efficiency PSCs are fabricated using volatile organic solvents with high toxicity,which is a major obstacle to the large-scale production of PSCs.Therefore,the development of environmentally friendly and low-toxic solvents is conducive to promoting the sustainable development of the field of PSCs.This thesis focuses on the green solvent preparation process of PSCs.The pinhole-free and large-grain MAPb I₃perovskite films were prepared by green anti-solvent assisted crystallization method.In addition,a Lewis base hexamethylphosphoramide(HMPA)solvent was proposed to treat the interface between the transport layer and the perovskite layer,with an aim to suppress the nonradiative recombination by passivation of the transport layer/perovskite interface through Lewis acid-base coordination.By characterizing the properties of films and corresponding devices,the effect of solvent processing on the power conversion efficiency(PCE)of PSCs was explored.(1)Perovskite films were fabricated by mixing green antisolvent diethyl ether(DE)and propyl acetate(PA).The results show that the mixed anti-solvent can induce grain growth,and the average grain size increases from 119 nm to 166 nm.At the same time,the carrier recombination life was prolonged by the use of mixed anti-solvent,indicating that the non-radiative recombination was inhibited.In addition,the devices treated with mixed anti-solvent show lower trap state density and faster charge mobility,indicating that the charge accumulation at the interface is reduced,which is conducive to promoting carrier migration.By introducing mixed solvents DE and PA,the power conversion efficiency(PCE)of the device was increased from 18.28%to 20.61%.This was mainly due to the increase in the fill factor(FF)(from 79.13%to 84.49%).The increase in FF is mainly attributed to the reduced ideal factor and to the improved diode junction quality.(2)The nickel oxide(Ni O_x)/perovskite interface was optimized by HMPA solvent to reduce the residual stress of perovskite film and promote the charge extraction and transport of Ni O_x/perovskite interface.The P=O bond of Lewis base HMPA is polar.The high electron density at the O site produces a large dipole moment and high basicity,which easily reacts with lead ion(Pb²⁺)to generate adjuncts at the interface,controlling the nucleation site and crystallization rate of perovskite.The residual lead iodide(Pb I₂)at the interface plays a role in passivation of defects.The results of conductivity and time-resolved photoluminescence showed that HMPA treatment was beneficial to the extraction of interfacial charge.Capacitance-voltage measurements and dark current-voltage curves further proved that HMPA solvent interface treatment can reduce trap state density and facilitate carrier transport.HMPA solvent treated devices achieved a PCE of20.91%and an open-circuit voltage of 1.09 V.Based on the above work,high quality perovskite films were prepared by environment-friendly low toxic solvent,which effectively reduced the non-radiation recombination and improved the carrier mobility.It is believed that this thesis provides a more environmentally friendly way for the sustainable and scalable development of emerging PSCs technologies.