Research On Defect Passivation And Photovoltaic Performance Of Perovskite Solar Cells

Perovskite solar cells(PVSCs)are regarded as one of the most promising photovoltaic technologies due to their low cost and high efficiency.Up to now,the highest authenticated power conversion efficiency(PCE)of PVSCs has reached25.5%.This high efficiency is mainly attributed to the excellent optoelectronic properties of perovskite materials,such as strong light-harvesting capacity ability,unique defect tolerant property,fast charge carrier mobility,low exciton binding energy,and tunable bandgap.However,the unsatisfactory stability of PVSC restricts its commercial applications.The defects at the surface and grain boundaries(GBs)of perovskite,as well as the interfacial defects between the transport layer and perovskite are the main factors leading to device degradation.Therefore,finding suitable strategies to reduce various defects in PVSCs is the key to improving efficiency and stability.The perovskite polycrystalline films contain numerous defects ascribed from the solution preparation process,including interstitials,vacancies and impurities,as well as non-coordinated ions at their GBs and surfaces.Such defects will influence the carrier transport via the formation of non-radiative recombination centers,thus hindering the further enhancement on the device efficiency and stability.Although various passivators have been proved to be promising materials for passivating perovskite films,there is still lack a deeper understanding of the effectiveness via different passivation methods.Here,the mechanism between anti-solvent dripping and additive doping strategies on the passivation effects in PVSCs is systematically investigated with a non-fullerene organic small molecule(F8IC).Such a passivated effect of F8IC is realized via coordination interactions between the carbonyl and nitrile groups of F8IC with Pb²⁺ions of MAPb I3.Interestingly,F8IC anti-solvent dripping can effectively passivate the surface defects and thus inhibit the non-radiative charge recombination on the upper part of the perovskite layer.Whereas,F8IC additive doping strategy significantly reduces the surface and bulk defects,and produces compact perovskite film with denser crystal grains,thus facilitating charges transmission and extraction.Therefore,these benefits are translated into significant improvements of the short circuit current density(Jsc)from 20.59 m A cm^-2 to 21.86m A cm^-2,and the champion PCE from 16.19%to 18.40%.The selection of optimal passivation strategy should also be considered according to the energy level matching between the passivators and perovskite.The large energetic disparity is unsuitable in additive doping,whereas it is expected in anti-solvent dripping.In nickel oxide(NiOx)-based PVSCs,the interfacial redox reaction between Ni³⁺metal cations sites and A-site cation salts is invariably ignored on the modification of NiOx hole transport layers(HTLs).This detrimental reaction will generate Pb I2-rich hole extraction barriers at the interface,which is likely to limit hole mobility and increase charge recombination,resulting in device open-circuit voltage(Voc)loss.Furthermore,the interfacial redox reaction will accelerate perovskite film degradation by deprotonating the precursor amine and oxidizing iodide to interstitial iodine,which induces the severe instability of NiOx-based PVSCs.Here,a physical separation strategy by introducing a buffer layer to obstruct the interfacial redox reaction is explored.The results demonstrate that the trimethylolpropane tris(2-methyl-1-aziridinepropionate)(SaC-100)depositing onto NiOx can serve as a buffer layer and surface modifier simultaneously.The ratio of Ni³⁺/Ni²⁺in NiOx is enhanced and the interfacial redox reaction between Ni³⁺and A-site cation salts is suppressed,which results in the improvement of conductivity and the reduction of interface defects,thus favoring hole extraction and reducing the Voc loss of device.Moreover,the interfacial energy level alignment and the morphology of perovskite are also optimized.As a result,the device with NiOx/SaC-100 achieves a PCE of20.21%with a Voc of 1.11 V,a Jsc of 22.37 m A cm^-2,and a FF of 81.36%,which is superior to the reference device with a PCE of 17.54%,a Voc of 1.05 V,a Jsc of 21.29m A cm^-2,and an FF of 78.09%.Furthermore,the device shows better light stability and thermal stability because of the blocking effect and defect passivation effect of SaC-100.