Active Layer Modulation,Interface Modification Of Perovskite Solar Cells And Corresponding Mechanisms

Promoted by the strategical goals of peaking carbon dioxide emissions and achieving carbon neutrality,photovoltaic technology has developed rapidly.Perovskite solar cells（PSCs）have experienced unprecedented fast development in photovoltaic field,with the power conversion efficiency（PCE）increasing from 3.8%to 25.5%during the past decade,as well as significantly improved device stability.However,the record efficiency of PSCs is still much lower than the Shockley-Queisser（SQ）limit.In addition,the device stability at current status cannot satisfy the commercial requirements.Here,we aim to achieve efficient and stable perovskite solar cells through moduation at the active layer and perovskite interface of PSCs.We further exploring the moduation mechanism behind non-radiative recombination suppression,so as to contribute to and provide ideas for the development of efficient and stable perovskite solar cells.Specific research are as follows:1.In view of the non-uniform and rough perovskite film through two-step technique,we proposed the synergistic modulation of MACl and DMF to prepare high-quality MAPbI₃ perovskite film.MACl is capable of inducing pureα-MAPbI₃formation with large grain size,however,poor surface morphology.The corresponding PSCs achieved higher filling factor（FF）,while the open circuit voltage(V_OC)was low.DMF modulated perovskite exhibits quite smooth and uniform morphology,however,DMF induces non-photovoltaic phase simultaneously.The corresponding PSCs achieved high V_OC,1.10 V,while the average FF was low.The MACl and DMF synergistically modulated perovskite film possesses pureα-phase crystallization and excellent surface morphology at the same time.The champion solar cell achieved an efficiency of 19.02%.In addition,the MACl and DMF synergistically modulated solar cells showed better long-term stability in N₂ atmosphere and dark conditions than the additive-free devices.The modulated device retained 91%of the initial efficiency after700 h storage,while the addition-free solar cell only retained 71%of the initial efficiency.2.For PSCs based on FAMAPbI₃,in order to optimize the SnO₂/perovskite interface,the effect of KCl modulation was studied.KCl modulation effectively reduces the hydroxyl group（-OH）on the surface of SnO₂ film and passivates-OH induced defect states.The lattice constants of FAPbI₃ and KCl are 6.39 A and 6.29 A,respectively,the mismatch between which is less than 2%,indicating KCl may serve as seed to induce FAPbI₃ crystal growth.Consequently,the grain size of perovskite based on KCl modulated SnO₂ is enlarged,demonstrating improved perovskite quality.In addition,KCl modulation improves the charge extraction and transport at the SnO₂/perovskite interface.By optimsing SnO₂/perovskite interface with KCl,the device efficiency was increased from 19.51%to 20.65%.At the same time,the stability of KCl modulated device is improved.After heating at 85°C in ambient environment（relative humidity is about 30%-70%）for 16 days,KCl modulated device maintained58%of the initial efficiency,while the control device only maintained 50%of the initial efficiency.Considering that KCl modulation can induce FAPbI₃ crystal growth,MAI-free devices were fabricated and a champion efficiency of 20.42%was achieved based on KCl modulation,close to that of the MAI-stabilized devices（20.65%）,providing a promising strategy to fabricate MAI-free PSCs.3.To further improve the performance of PSCs,we designed trimethylphenylmethylammonium iodide（TMPMAI）by introducing one aromatic phenyl to the traditional alkyl quaternary ammonium to modulate the perovskite/Spiro-OMe TAD interface.TMPMAI electrostatically adsorbs on the surface of perovskite film and effectively supresses non-radiative recombination.We further explored the mechanism of the supressed non-radiative recombination and found:TMPMAI modulation passivated defects,and a gradient energy level distribution was formed at perovskite/Spiro-OMe TAD interface,resulting in the enhanced built-in electric field.The mechanism of TMPMAI modulation was investigated by DFT calculations,and the introduced phenyl took an important role in the modulation process.The device efficiency was increased from 21.38%to 23.11%through modulation.The maximum output efficiency reached 22.76%at the maximum power point.TMPMAI modulation endows the device with improved the long-term stability and thermal stability.The modulated device maintained nearly 80%of the initial efficiency after heating at 85°C in ambient environment（relative humidity of about 20%-40%）for 15 days,while the control device only maintained 63%of the initial efficiency.4.To stablize perovskite itself,Eu Br₂ was incorporated into the perovskite layer.The device efficiency was not influenced much by Eu Br₂,with champion efficiency of22.92%and 23.04%for the control and Eu Br₂ incorporated devices,respectively.Whereas Eu Br₂ incorporation inhibitsδ-FAPbI₃ in thin films and slows down the degradation rate of perovskite film in ambient environment under certain conditions,providing a promising strategy to improve the stability of perovskite material.