Architectural Design And Performance Of Formamidine Based Perovskite Solar Cells

Hybrid organic-inorganic perovskites have attracted increased attraction over the past seven years and have have been considered as significant optoelectronic semiconductor materials.The main advantages of perovskites materials are simple processability,abundance of ingredients,tunable bandgap,high extinction coefficient,high charge mobility and bipolar transport nature.However,perovskite solar cells(PSCs)based on perovskite materials as the active layer still have some problems to be solved.In particular,understanding the principle to design rational microstructure of perovskites and carrier transport materials,and relation between the microstructure and performance of PSCs is of great importance.It is still a grat challenge to further enhance charge transport kinetics,to improve reproducibility and mitigate hysteresis,and to boost device stability and more.In response to these problems,the device structure and interface are optimized by adjusting the composition and morphology of perovskite materials,selecting different kinds of n-type semiconductors and designing the microstructures.We aim at providing some new design ideas and optimized parameters to improve the optical-physics and optoelectronic properties of the device.The main contents of this paper are as following.(1)Three-dimensional hierarchical TiO2-CdS-RGO composites were prepared as the electron transport layer(ETL)of formamidine lead iodine(FAPbI3)PSCs.Compared with single TiO2 and binary composite,TiO2-CdS-RGO has stronger fluorescence quenching ability and lower photoinduced electron-hole recombination rate,suggesting an excellent electron transport ability.Jsc and PCE of the device based on TiO2-CdS-RGO increases 14.5%and 36.3%,respectively compared with that of PSCs based on single TiO2 ETL.TiO2-CdS-RGO can improve the photoelectric properties because the high specific surface area of mesoporous TiO2 is conducive to perovskite penetration and promote electron transport efficiency.The matched energy level of perovskite,CdS and TiO2 is conducive to promote electron extraction and reduce the recombination rate of photogenerated carriers.RGO nanosheets with good conductivity can serve as the main electron transport network and provide high-speed charge transport paths that are crucial for enhancing the photoelectric conversion performance of PSCs.(2)Al2O3 layer passivated TiO2 nanorods array were synthesized as an ETL for thermal evaporation-route synthesized FAPbl3 perovskite solar cells.PSCs based on evaporation-fabricated FAPbI3 absorption layer and Al2P3-TiO2 ETL display excellent photoelectronic performance,showing a high photoelectric conversion efficiency of 14%with negligible hysteresis,excellent reproducibility and stability.The greatly improved performances can be attributed to the following three factors.Firstly,Al2O3 buffer layer as a barrier can effectively retard electrons in ETL reverse transport and impede charge carrier recombination.Secondly,Al2O3 passivation can enhance the TiO2/FAPbI3 interface contacts,alleviate the electron trapping effect resulted from the surface defects at TiO2/perovskite interface,benefiting for electron extraction to be transported directly toward FTO.Thirdly,the evaporation synthetic route is helpful to get extremely homogeneous FAPbl3 film without any pinholes and compact interface,which contribute to improve the photoelectric properties and stability of the device.(3)We designed a TiO2/C60/CSPbIxBr3-x/FAPbIyBr3-y multi-heterojunction PSCs with optimized energy band alignment by precisely adjusting I:Br proportion in CsPbIxBr3-x/FAPbIyBr3-y double perovskite layer.The high-mobility fullerene of C60 can passivate interfacial trap states,thus effectively further promote charge dissociation/transport.The introduction of CsPbIxBr3-x between FAPbIyBr3_y and ETL results in improved electron separation efficiency and current density.Owing to the conduction band offset,the multi-heterojunction with energy band alignment eliminates energy barriers at the heterojunction interface and facilitates the electrons and holes flowing to the opposite side,therefore enhances the charge extraction efficiency and boosts charge transport ability.PSCs based on double perovskite layer demonstrate enhanced photovoltaic performance,with an outstanding PCE of 16.3%with negligible hysteresis and excellent reproducibility,simultaneously exhibiting remarkable stability in ambient atmosphere,thermal and moisture conditions.(4)For the sake of boosting the electron extraction efficiency in PSCs and improving the balance of electron-hole transport,we design the novel soluble pyrrole modified fullerene as the electron extraction material(EEM)and fabricated bulk heterojunction(BHJ)PSCs by one-step co-deposition of perovskite/Pyr-fullerene mixtures.For one thing,pyrrole modified fullerenes are miscible and can significantly increase the grain size and reduce the grain boundaries,thereby reducing charge recombination loss caused by the trap states.For another,bulk heterojunction interpenetrating network enlarges the interfacial area between the perovskite and EEM facilitates balanced charge transfer.Simultaneously,the modified fullerene has optimized band alignment,the hybrid BHJ exhibits quenched fluorescence intensity,decreased electron lifetime and large recombination resistance,which indicates effective electron extraction and suppressed electron-holes recombination.The optimal PSCs achieve a PCE of up to 18.9%with virtually no hysteresis and suppress the degradation over time.(5)MOF derived ZnO(MZnO)was used as the ETL for the mixed cationic PSCs.MZnO with polyhedral morphology and a large number of internal channels can induce higher light absorbance efficiency and enhance the light utilization of perovskite.The introduction of MZnO results in more efficient electron extraction and suppressed electron-hole recombination rates than ordinary nanoparticle ZnO,and thus promotes electron transport and increase JSC and FF.MZnO-induced improvements in the interface structure of the PSCs greatly enhances the performance of the device,resulting in a Voc of 1.11 V,a Jsc of 22.1 mA cm-2,a FF of 0.74 and a PCE of 18.1%with almost no hysteresis.At the same time this device in a certain humidity environment has outstanding stability.The high efficiency of PSCs stems from enhanced carrier extraction efficiency as well as increased interfacial area and improved light utilization between ETL and PVSK.