Study Of Additive-optimized Functional Layers To Enhance Photovoltaic Performance Of Perovskite Solar Cells

ABX₃ structured polycrystalline perivskite materials with wonderful optoelectric properties,tunable band gap and controlled synthesis process have shown great promise in the field of photovoltaic(PV)devices,such as perovskite solar cells(PSCs),photodetectors and light emitting diodes.Currently,PSCs have become a hot research topic in the PV fields with a high power conversion efficiency(PCE)of over25.8%.In the process of their application,scientific and technical isues such as long-term stability,lead toxicity and large area preparation still need to be solved.The selection and quality optimization of the functional layer material systems is the way to solve the above problems.To this end,we use additive engineering in this thesis to regulate the crystal growth dynamics of polycrystalline perovskite films,optimize the optoelectric properties of charge transport layer and passivate the internal defects of devices in a full range maner to improve the PV performance of PSCs,and reveal the physical mechanisms related to the additive regulation.The innovative results achieved are as follows:1.The presence of defects within electron transport layers(ETLs),perovskite films and at their interfaces greatly affects the PCE and stability of PSCs.We proposed a facile and effective defect passivation strategy in a synergistic maner by introducing chelating agents containing alkali metal cations,i.e.sodium tartrate(STA)/potassium sodium tartrate(PSTA),into the SnO₂ aqueous colloidal dispersions.The chelating effects of the additive and the presence of alkali metal ions synergistically regulated the growth dynamic process of SnO₂ nanocrystals,improved the film-forming quality of ETLs and their electrical properties,and provided a good platform for the preparation of high-quality perovskite films.In particular,the freely movable K⁺and Na⁺ions in the additives enter the perovskite films in the form of thermal diffusion to passivate the uncoordinated halide defects through ionic interactions.Finally,the PSCs with STA-SnO₂ and PSTA-SnO₂ as ETLs achieved20.38%and 21.14%PCEs,respectively,and the stability of the devices was effectively improved.2.To further achieve the full range passivation of defects within devices and precise energy level alignment among functional layers,we developed a combination of additive-doped ETLs and anti-solvent post-treatment of perovskite films to enhance the PV performance and stability of PSCs:i.e.,the introduction of phenethylammonium chloride(PEACl)into the SnO₂ aqueous colloidal dispersions optimized the performance of ETLs.The N atoms in-NH₂ contained in the additive can coordinate with Sn⁴⁺ions,which effectively improves the agglomeration of SnO₂nanoparticles,while the presence of Cl^-also effectively fills the oxygen vacancy defects in SnO₂ ETLs,thus obtaining ETLs with high flatness and good crystalline quality.In adidition,the freely Cl^-ions can also participate in the crystal growth dynamics of perovskite films,assisting in optimizing the crystalline quality of perovskiye films.To further improve the interfacial properties of perovskite/hole transport layer(HTL),p-type conductive material N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine(NPB)was introduced into the antisolvent chlorobenzene to prepare perovskite films,and the cross-linked distribution of NPB on the surface and at the grain boundaries of perovskite films effectively passivated the uncoordinated Pb²⁺defects,which not only achieves a full range passivation of defects within devices,but also enables the formation of gradient heterojunction between the upper perovskite film and Spiro-OMe TAD HTL,providing a convenient channel for effective migration and transport of hole carriers.Ulitimately,PSCs synergistically optimized by PEACl and NPB obtained a PCE of21.88%.Moreover,due to the excellent hydrophobic properties of PEACl and NPB molecules,the high decomposition point,and the full range passivation of defects within the devices,the above devices exhibit great tolerance to moisture and temperature,which effectively enhancs the long-term operational stability of PSCs.3.The inferior work function,electrical conductivity,hydrophilic properties,and film-forming quality of PEDOT:PSS HTLs are the main factors limiting the enhancement of PV performance of p-i-n structured PSCs.We used additive modulation combined with interfacial modification to achieve a synergistic modulation of the photoelectric properties of PEDOT:PSS HTLs,the growth dynamic process of perovskites,and the interfacial properties.That is,HAuCl₄ was introduced into the PEDOT:PSS aqueous solution,and the redox reaction between them induced the phase separation of PEDOT:PSS and effectively regulated the electrical conductivity and surface morphology of HTLs.On this basis,NPB with good electrical conductivity,strong hydrophobicity and down-conversion to UV light was selected to further modify HAuCl₄-PEDOT:PSS films.The more suitable energy level structure of NPB compared with that of perovskite and HAuCl₄-PEDOT:PSS films promotes the efficient hole transport,while the coordination of N atoms with uncoordinated Pb²⁺ions passivates the defects at the interface,further reducing the non-radiative V_oc loss of the device.The enhanced quality of perovskite films,the local surface plasmon resonance generated by gold nanoparticles on HAuCl₄-PEDOT:PSS films,and the scattering effect of the particles will also enhance the utilization of solar energy.Based on the above synergistic optimization strategy,PSCs on rigid substrates achieved a PCE of 19.20%with a Voc of 1.077 V,almost hysteresis-free behavior,and enhanced stability.The corresponding flexible PSCs also achieved a PCE of 14.04%with strong wrinkle resistance.4.Preferred orientation growth of organic-inorganic hybrid perovskite grains affects the PV performance of PSCs.However,the formation energy of other crystal planes is higher than that of(110)crystal plane,so it is difficult to achieve the preferred orientation growth of perovskite films along other crystal planes,which is even more difficult for Sn-Pb binary perovskite materials due to the faster crystallization rate.We have successfully achieved the preferred orientation growth of Sn-Pb binary perovskite films along(224)crystal plane by adopting simple methods combined additive engineering with ultrasonic treatment(UST).That is,the nucleation and growth dynamic process of polycrystalline perovskites were regulated by introducing a high melting point additive tartaric acid(TA)with both complexation and antioxidant properties,into the low toxic MA_0.9Cs_0.1Pb_0.75Sn_0.25I₃ perovskite precursor solution,where the formation of PbI₂/SnI₂·TA intermediate phase regulated the crystallization rate of Sn-Pb binary polycrystalline perovskites,improved crystallinity of the films,reduced the defect states associated with Sn⁴⁺,and inhibited the decomposition of the films.Subsequently,the interaction between PbI₂/SnI₂·TA and MAI/Cs I was further modulated by ultrasonication of the above solution for different times,and a transition of preferred film orientation growth of the Sn-Pb binary polycrystalline perovskite films along the(110)crystalline plane to the(224)crystalline plane was finally ahieved.When TA-doped perovskite precursor solution was ultrasonicated for 15 min,the perovskite film with preferred orientation growth along the(224)crystal plane was successfully obtained,and the PSCs prepared with these films achieved a PCE of 15.59%.The PCE was improved by 25.32%and 8.64%compared with those with preferred orientation growth along(110)crystal plane without any treatment and those with TA but without UST,respectively.In addition,PSCs with preferred growth orientation along(224)plane have less hysteresis and higher stability.This thesis not only privides an effective additive synergy optimization strategy for improving the PV performance of PSCs,but also elucidates the mechanism of action of different regulatory strategies,providing novel ideas for the design of additive engineering strategies and an experimental and theoretical basis for the mechanism of enhanced performance of devices.