High Efficiency Of Inverted Perovskite Solar Cells Via Interface Modification

Since 2009,organic-inorganic hybrid perovskite materials have attracted wide attention in the field of perovskite solar cells(PSCs).In just 10 years,the certified power conversion efficiency(PCE)of the organic-inorganic hybrid PSCs has exceeded25%.At present,the organic-inorganic hybrid PSCs with high efficiency usually adopted a mesoporous structure or planar n-i-p structure.However,compared to the PSCs with n-i-p structure,the PCE of the PSCs with planar inverted p-i-n structure is inferior.Nonetheless,the inverted PSCs advance in simple structure,low-temperature preparation,and small hysteresis effect,which are more appealing to the commercialization of PSCs.However,the main bottleneck of the inverted PSCs is the lack of optical management and carrier dynamics optimization.The latter,in particular,severely limits the increase of open-circuit voltage.Therefore,we focus on the interface engineering,by modifying the interface between the perovskite layer and hole transport layer(HTL).The quality of perovskite thin film and the transport of photogenic carriers can be improved.Accordingly,the PCE and stability of PSCs are improved.In this thesis,the interface energy band matching,interface defect passivation,and the construction of an interface bridge are carried out from the following three aspects of work:(1)MAI interface band modulation mechanism and optical management process optimizationThe chlorine-doped lead methylamine iodide(MAPbI_3-xCl_x)was used as a light-absorbing layer in PSCs.MAI was used to modify the interface between HTL and the perovskite layer,and the band bending was formed at the interface of the perovskite layer near the HTL to accelerate the separation of photogenic carriers and the transfer of the hole to the transparent electrode,so as to improve the performance of the PSCs.We demonstrate a modified one-step fabrication method for the bandgap tuning of the perovskite layer by designing the iodide concentration gradient.Prior to the perovskite precursor solution spin-coated,different concentration of MAI solution was pre-coated on PEDOT:PSS layer to form iodide concentration gradient in the perovskite layer.Fast hole extraction and short lifetime due to the iodide concentration gradient were confirmed by photoluminescence measurement.By optimizing the MAI concentration with 4 mg/m L,the modified PSCs exhibited a PCE of 16.67%due to an increase in J_scfrom 19.66 to 23.52 m A/cm² and an increase in V_oc from 0.97 to 1.01 V.These values are significantly higher than PSCs using conventional one-step fabrication method without pre-coated MAI layer,which exhibit the efficiency of only 14.8%.We think that this new approach is an effective way to enhance the performance of PSCs.(2)Ultra-thin PTAA passivated perovskite film and carrier management optimizationThe chlorine-doped lead methylamine iodide(MAPbI_3-xCl_x)was used as the absorption layer of the inverted PSCs,and the ultra-thin polytriarylamine(PTAA)is used to achieve the passivation and interfacial composite inhibition of defects at the interface between perovskite layer and the HTL.One-step anti-solvent deposition method is widely applied in inverted PSCs.However,the anti-solvent processed film typically exhibits a small grain size and abundant defects.Herein,we propose a facile passivation approach using the ultrathin PTAA layer to passivate the interfacial and grain boundary defects.An energy band alignment is realized by introducing an ultrathin PTAA layer(valence band:-5.2 e V)sandwiched between the perovskite layer(valence band:-5.4 e V)and the PEDOT:PSS layer(valence band:-5.0 e V)to suppress interfacial recombination and accelerate hole transfer.By optimum design of the PTAA layer,we fabricate the PSCs with a PCE of 19.04%,a fill factor(FF)of 82.59%,and J_scof 21.38 m A/cm².To the best of our knowledge,the FF is the maximum value among inverted Chlorine-doped methyl PSCs.After storage in an ambient condition for 10 days,the PCE of the PSCs with PTAA modification is still maintained at the 80%level,indicating the substantially improved stability.Our work provides an effective method to boost the PSCs with enhanced efficiency and stability.(3)Bridging mechanism and interface quality optimization of alcohol-soluble small moleculeFA_0.2MA_0.8PbI_3-xCl_x is used as the perovskite precursor,and interface bridging is used to passivate the interface to improve the carrier transport efficiency.Interface engineering is widely applied in the one-step anti-solvent deposition for elevating the efficiency of the PSCs.Herein,an alcohol-soluble small molecule,namely2-Mercaptoimidazole(MI),inserted between the HTL and perovskite layer to form a cross-linking bridge,which is built through:(i)Coulomb interaction between the negatively charged MI and positively charged poly(3,4-ethylene dioxythiophene)(PEDOT);(ii)electrostatic interaction between imidazolium cation and iodide anion in perovskite.The cross-linking bridge can accelerate the hole transmission and inhibit interfacial recombination.Hence,by the optimum design of MI concentration,the hysteresis-free devices with a high PCE of 20.68%are obtained.The overall efficiency increase is due to significantly enhanced J_sc from 21.28 m A/cm² to23.45 m A/cm² and slightly raised V_oc from 1.06 to 1.08 V,suggesting that the MI modified layer can effectively improve the performance of the devices.Moreover,the unencapsulated devices with MI interfacial modification show better environmental stability compared to the reference devices.This facile interfacial approach is promising for future commercialization of inverted PSCs.In conclusion,we first propose an interface iodine ion concentration to achieve energy level alignment.Then the ultra-thin PTAA layer is developed to passivate the interface.Finally,we employ the alcohol-soluble small molecules to implement interface passivation between the perovskite film and HTL.Accordingly,we improve the performance of the inverted PSCs through these three works and give a positive insight into promoting the further development of perovskite solar cells.