Investigation Of The Effect Of Interface Regulation On The Efficiency And Stability Of Perovskite Solar Cells

Perovskite solar cells(PSCs)are considered to be the most promising nextgeneration photovoltaic devices due to their high efficiency,simple preparation and low cost.The power conversion efficiency(PCE)of PSCs has been rapidly improved by components adjustment,interface regualation,charge transport layer optimization.At present,the certification PCE has reached 25.8%.The perovskite light-absorbing layers are usually prepared by solution methods.The rapid crystallization of the perovskite leads to the formation of defects during film fabrication,thereby reducing the device efficiency.These defect states are more likely to form at the interface of the perovskite than inside the perovskite film.At the same time,interface defects can accelerate the decomposition of perovskite,thereby shortening device lifetime.In this case,this thesis adopts an interface regulation strategy to passivate the surface defect states of perovskite to achieve the purpose of improving the efficiency and stability of PSCs.The main contents of this thesis are as follows:(1)The 2D perovskite is formed in situ on the surface of 3D perovskite via chemical interactions between diethylammonium iodide(DAI)and PbI6 octahedra,which passivates the interfacial defects of perovskite to improve the efficiency and stability of PSCs.The excess PbI2 on the surface of the perovskite film treated with DAI is consumed and transformed into 2D perovskite,thereby reducing deep-level defects and nonradiative recombination.Moreover,the 2D/3D structure can regulate the energy level alignment,enhance the charge extraction,and improve the open-circuit voltage(VOC)Finally,compared with the control device,the PCE of the DAI-treated device increases from 21.58%to 23.50%.The maximum power point output efficiency of the control device decreases by 10.59%within 300 seconds,while that of the DAI device decreases by only 2.75%.The unencapsulated devices stored in air(a relative humidity of～10%)for more than 500 hours can still retain 97%of their initial PCE,demonstrating long-term placement stability.(2)To further improve the performance of the device,4-trifluoromethylphenylamine hydrochloride(TFPhFACl),a dipole molecule,was used for the first time to regulate the top interface of the perovskite.Different functional groups in TFPhFACl have different effects on device performance.Firstly,TFPhFA+ has a large dipole moment,which can form a dipole layer on the perovskite surface,effectively promoting the extraction and transmission of charges from the perovskite active layer to the hole transport layer.Secondly,the TFPhFA+ cations coordinate with PbI6,which suppresses nonradiative recombination of perovskite.Finally,the recrystallization of 3D perovskite induced by chloride ions can improve the film quality.As a result,the control PSC without TFPhFACl treatment delivers an efficiency of 21.9%with a VOC of 1.08 V,a fill factor(FF)of 79.77%and a short-circuit current density(Jsc)of 25.49 mA/cm2.Compared with the control PSC,the champion TFPhFACl treated PSC delivers a much higher PCE of 24.0%with a Voc of 1.16 V,an FF of 81.26%and a Jsc of 25.42 mA/cm2.The device shows no decrease in PCE after 1500 hours stored in the air(relative humidity below 20%),indicating the good stability.(3)In order to optimize the bottom interface of perovskite and electron transport layer(ETL),amino trimethylphosphonic acid(ATMP)was used to regulate the growth of TiO2 grains,energy level alignment and improve the interface contact between perovskite and ETL,which can achieve an increase VOC and PCE of devices.The results show that ATMP can inhibit the hydrolysis of Ti4+ by forming a chelate with the phosphoric acid group in the molecule,prevent the aggregation and rapid deposition of TiO2 particles.Therefore,the growth of TiO2 grain can be regulated in this way.In addition,ATMP can regulate the energy band of TiO2 to achieve a more matching energy level arrangement,which facilitates carrier extraction and electron transport,improving the Voc of the device.Furthermore,ATMP can reduce the deep level defects on the surface of TiO2 and enhance the interface contact between TiO2 and perovskite;thus,the transfer of charge carriers at the interface is enhanced as well.Compared to the control devices,the average Voc of PSCs prepared with this ETL increases from 1.17 V to 1.19 V,and the average PCE increases from 23.59%to 24.10%.The maximum power point output efficiency of the control device decreases by 11.8%from 23.7%to 20.9%within 300 seconds;in contrast,the ATMP-TiO2 device decreases from 23.8%to 22.2%,a decrease of only 6.7%,showing better light stability.In this thesis,both the top and the bottom interfaces of the perovskite are regulated to reduce the defect state,regulate the energy level matching,thereby improve the efficiency and stability of the device.This work provides new ideas for the design of functional groups of perovskite passivators,and provides a reference for the preparation of high-quality ETL and the modification of the bottom interface.It is significant to promote the commercial application of perovskite solar cells.