Research On Reducing Energy Loss Of Perovskite Solar Cells Via Bulk Passivation And Interface Optimization

In the past decade,perovskite solar cells（PVSCs）have experienced rapid development,and their maximum certified power conversion efficiency（PCE）has reached 25.7%,exhibiting great commercial prospect.Nevertheless,this PCE value is still far behind the Shockley-Queisser limit due to the severe energy loss(E_loss)within the device.The E_loss mainly comes from the bulk defects or interfacial defect and the large energy level offset between the different layers.Reducing the E_loss of PVSCs is crucial to further improve the PCE and stability of devices.Therefore,in view of the E_loss problem in PVSCs,several strategies of bulk passivation and interface optimization were proposed in this work to reduce the E_loss in PVSCs and further improve the performance and stability of devices.The main research contents include the following seven parts:Firstly,biological material dopamine（DA）was doped into perovskite precursor solution to prepare a highly crystalline perovskite film with（110）crystal orientation.DA molecules can interact with the uncoordinated lead and iodine ions,which reduced the uncoordinated ion defects and inhibited the migration of I^-ions.Consequently,the PCE of the optimized device reaches 21.03%,which is obviously higher than that of the reference device（18.31%）.At the same time,the optimized device exhibits better stability due to the improved crystallinity of the perovskite film and the weakened ion migration behavior in the device.Secondly,we used three thiophene based molecules with different dipole moments to optimize the Sn O₂/MAPb I₃ interface,so as to reduce the E_loss at this interface.The thiophene based molecules passivated the-OH defects on Sn O₂ electron transport layer（ETL）surface by binding with them.At the same time,the electron transfer between the thiophene based molecules and the Sn O₂ ETL reduces the surface work function（W_F）of the Sn O₂ and improves the electron transport efficiency of the Sn O₂/MAPb I₃ interface.In addition,thiophene based molecules also improved the crystallinity of the upper perovskite films.Consequently,the PCE of the optimized device was increased from 17.54%to 20.61%,and the device stability was also improved.Thirdly,the crystallization process of perovskite films was regulated by adding TAPC to the antisolvent.The TAPC additive not only reduces the bulk defects of perovskite films,but also changes the surface energy level,and promotes the formation of p/p⁺homojunction on the upper surface of perovskite film.At the same time,the introduction of Th MAI and Th EAI at the Sn O₂/perovskite interface effectively reduced the defects of the interface and generated an interfacial electric field.The p/p⁺homojunction and interface electric field were formed on the upper and bottom surfaces of perovskite film under the synergistic effect of TAPC and Th EAI,which increases the built electric field and reduces the non-radiative recombination loss inside the device.As a result,the PCE of PVSCs increased from 19.15%to 23.44%,and the stability of PVSCS was also significantly improved after optimization.Fourthly,a BF₄^-anions assisted molecular doping（AMD）strategy was proposed to reduce the E_loss at the buried interface of inverted PVSCs.On the one hand,AMD strategy improves the doping level and hole transport capacity of PTAA and Poly-TPD hole transport layers（HTLs）and reduces the E_loss at the HTL/perovskite interface.On the other hand,the BF₄^-anions on HTLs surface increases the formation energy of iodine vacancy（V_I）on the bottom surface of perovskite by forming Pb-F bonds with lead ions in perovskite,which results in the energetic transformation from N-type to P-type on the bottom surface of perovskite layer.The formation of p-n homojunction on the bottom surface of perovskite layer increase the built-in electric field and charge separation efficiency of the device,and effectively reduce the E_loss at the HTL/perovskite buried interface.The optimized device achieved the highest PCE of 24.26%and exhibited good stability.Fifthly,three different dipole layers were introduced at the ITO/MAPb I₃ interface of HTL-free inverted PVSCs to reduce the E_loss at the interface.Firstly,these dipole layers passivate the-OH defects on ITO surface by binding with them,which reduces the non-radiative recombination of ITO/MAPb I₃ interface.In addition,the electron transfer between these dipole layers and ITO reduces the electron density of ITO and adjusts its surface W_F,which improves the hole transport efficiency at the ITO/MAPb I₃ interface and reduces the accumulation of hole carriers at this interface.Moreover,the dipole layers also improve the crystallinity of the upper perovskite film and reduce the non-radiative recombination loss caused by the bulk defects.Consequently,the HTL-free PVSCs achieved a maximum PCE of 20.19%and good stability after dipole layers optimization.Sixthly,we successfully synthesized two-dimensional（2D）Nb₂CT_x MXene nanomaterial and improved its electron transport capacity through amino functionalization.Then the optimized Nb₂CT_x MXene was used as ETL to improve electron transport efficiency at the ITO/perovskite interface.Firstly,the-F groups on Nb₂CT_x MXene surface were replaced by-NH₂groups after amino functionalization,which reduces the W_F of Nb₂CT_x MXene and improves the electron transport efficiency at the ITO/perovskite interface.Secondly,the Nb₂CT_x MXene with abundant-NH₂ groups can reduce the crystallization rate of perovskite films by forming hydrogen bond with the I^-ions in perovskite,resulting in improved crystallization quality of the films.As a result,the PVSCs based on T-Nb₂CT_x ETL and doped with T-Nb₂CT_x additive achieved the highest PCE of 21.79%and exhibited good stability.Seventhly,we successfully prepared 2D Nb₂CT_x MXene nanomaterial.The Nb₂CT_xMXene was treated with oxygen plasma to improve its hole transport capacity and used as HTL to improve the hole transport efficiency at the ITO/perovskite interface of inverted PVSCs.The number of-O groups on Nb₂CT_x MXene surface was increased by oxygen plasma treatment,and the W_F of Nb₂CT_x MXene was increased from 4.68 e V to 5.04 e V.The increased W_F of Nb₂CT_x MXene results in an upward band bending at the Nb₂CT_x/perovskite interface,which enhances the hole transport and reduces the non-radiative recombination E_loss of at this interface.Consequently,the optimized inverted PVSCs obtained highest PCE of 20.74%and had good stability.