Functional Molecules Controlling The Film Growth And Their Photoelectric Properties In Perovskite Solar Cells

In recent years,perovskite materials have attracted widespread attention due to their many outstanding properties.In the photovoltaic（PV）field,the power conversion efficiency（PCE）of perovskite solar cells（PSCs）has jumped from 3.8%to 25.7%in ten years.In addition,in the optoelectronics field,the external quantum efficiency（EQE）of perovskite light-emitting diodes（Pe LEDs）has been increased from 0.76%to 28%,driving the vigorous development of perovskite materials.Despite the rapid development,scientific and engineering issues,such as its instability,versatility,cost,and large-area fabrication still need to be resolved for future commercial applications.This is an essential step toward obtaining highly crystalline and low-defect perovskite thin films.In this thesis,the efficiency and stability of formamidine（FA）-based perovskite solar cells are focused.The performance of the device is improved by regulating crystal growth and omnidirectional passivation of film defects states density.Further,the mechanism of different additive control strategies is revealed.The energy loss mechanism of the device is clarified to understand the physical working mechanism.The main contents are as follows:（1）Self-polymerized molecules stabilize FAPbI₃ perovskite solar cells.Aiming at the phase transition and humidity instability of FAPbI₃ PSCs,an in-situ polymerization controlled growth（IPCG）strategy is applied to improve the efficiency and stability of FAPbI₃ perovskite solar cells in Chapter 3.Polymerization of 2-（Dimethylamino）ethyl methacrylate（DMAEMA）contained in the antisolvent（toluene）created polymers（denoted as Poly（D））is employed to simultaneously increase the perovskite grain size,passivate defects,stabilize the black phase,and block moisture penetration,thus greatly improving photovoltaic performance and stability.The resulting FAPbI₃-based PSC（FTO/Sn O₂/Perovskite/Spiro-OMe TAD/Au）delivered a PCE of～21%（cf.～16.0%PCE for the pristine FAPbI₃ device）.Further,the polymerization strategy delivers PSCs with remarkable stability,with 100%of the initial PCE performance being retained for 104 days under ambient conditions（room temperature,relative humidity=50±5%,dark indoor environment）without encapsulation.（2）Bimolecular synergistic effect for efficient and stable FA-based perovskite solar cells.To address the non-radiative recombination caused by vacancy defects and stability problems,in Chapter 4,additives and stabilizers,namely safe and non-toxic acesulfame potassium（Ace-K）and pentaerythritol tetraacrylate（PETA）,are employed.The perovskite film is prepared by a two-step deposition method.Ace-K has abundant functional groups to form strong interactions with lead ions by being introduced into the lead iodide precursor,regulating crystallization nucleation and passivating defects.The potassium ions filled in the interstitial in the lattice suppress the FA-I Franklin defect to reduce hysteresis and improve the optoelectronic properties of the device,resulting in EQE_EL of 7.3%and a drop in non-radiative recombination loss from 111 m V to 72 m V.PETA is dissolved in chlorobenzene and coated on the surface of the perovskite film.Based on the structure（FTO/Sn O₂/Ace-K perovskite/PETA/Spiro-OMe TAD/Au）,the PCE of 21.9%（19.7%for the control device）,excellent V_oc of 1.18 V and3%hysteresis factor are obtained.In addition,the device maintains an initial efficiency of 88%for 1800 hours benefiting from the network structure inherent hydrophobicity of PETA under ambient conditions（room temperature,relative humidity=60-70%,dark indoor environment）.Furthermore,the PSC maintains more than 80%of its initial efficiency under 440 hours of continuous illumination at a maximum power point（MPP）（test conditions:argon atmosphere,temperature=（35±5）℃）.（3）Multifunctional molecular additive enables perovskite bifunctional diode with high photovoltaic and electroluminescent performance.In Chapter 5,we develop bifunction diode for advanced application.Integration of photovoltaic（PV） and electroluminescent（EL） functions and/or units in one device is attractive for new generation optoelectronic devices but it is challenging to achieve highly comprehensive efficiency.The defect-induced nonradiative recombination limits the development of photovoltaic/luminescence bifunctional diodes.Therefore,it is crucial to develop strategies to reduce nonradiative recombination and minimize V_ocloss.Based on the excellent results obtained in the previous work,the fifth chapter used 3-sulfopropyl methacrylate potassium salt（SPM）additive to tackle this issue.SPMs not only induce large grain size during the film formation but also produce a secondary phase of 2D K₂PbI₄to passivate the grain boundaries（GBs）.In addition,its sulfonic acid group and potassium ion can coordinate to lead ion and fill the interstitial defects,respectively.Thus,SPM holistically reduces the defective states and suppresses nonradiative recombination loss.As a result,planar PSC（SnO₂/perovskite/spiro-OMe TAD）delivers a PCE of～22%,with a maximum V_ocof 1.20 V（E_g=1.57 eV）.The V_oc is 94%of the radiative V_oc limit（1.28 V）,higher than the control device(V_oc of 1.12 V).In addition,the reciprocity between PV and EL is also correlated to quantifying the energy losses and understanding the device physics.When operated as a light-emitting diode（LED）,the maximum EL external quantum efficiency(EQE_EL)is up to 12.2%(EQE_EL values of 10.7%under an injection current of short-circuit photocurrent),thus leading to high-performance PV/EL dual functions.In addition,this work demonstrates the reciprocal relationship between photovoltaic and luminescent properties,and quantifies energy losses to understand the physical working mechanism of components.