Research On Electrode Interfacial Materials For Efficient Polymer Solar Cells

Bulk-heterojunction polymer solar cells(BHJ-PCSs)have been attracting much attention due to the advantages of easy fabrication,low cost,light weight,applicable to large areas and flexible devices.As the key parameters of industrialization,the power conversion efficiency(PCE)and stability of polymer solar cells urgently need to be improved.As core functional layers of solar cells,the active layer and the interfacical layer with excellent electrical,optical and energy level characteristics have become a research hotspot in the field of organic photovoltaic.To improve the efficiency of polymer solar cells,this paper has carried out the research on high-performance interfacial modification materials,and our study has foucs on the concept of"determining optimized strategies,elucidating on micro-mechanism and improving device performance".The main contents are as follows:1.The simple and facial approach of spin-coating technology with post heat and ultraviolet-ozone treatment is performed on niobium oxalate hydrate as precursor to prepare Nb2O5 interfacial layer with ultra-high transmittance.The ultraviolet photoemission spectroscopy results confirm that Nb2O5 with a work function of 4.85 eV is suitable for employing as anode buffer layer(ABL).The average PCE of the P3HT:PCBM-based fullerene devices with Nb2O5 ABL reaches to 4.01%,surpassing that of the control devices with ITO/PEDOT.PSS ABL(3.69%).Further investigations on the PBDB-T:ITIC-based non-fullerene PSCs with Nb2O5 ABL demonstrate that a PCE as high as 8.67%can be achieved,which is superior to that of device modified by PEDOT:PSS ABL(8.03%).2.We fabricated the active layer with vertical phase separation on the electron transport layer of a titanium(?)oxide bis(2,4-pentanedionate)(TOPD)and obtained a PCE of 10.23%in inverted PSCs.In this device,TOPD with high transparency is an excellent cathode buffer layer due to its outstanding electron-collecting and hole-blocking functions.Meanwhile,benefiting from the the vertical phase separation properties of PBDB-T:ITIC-M blend film,the vertical concentration distribution of the donor and acceptor was formed in the active layer,which ensures effective exciton dissociation and simultaneously offers independent pathways for charge transportation.The combination of their virtues facilitates the high enhancement of open circuit voltage(Voc)up to 0.21 V besides the increased short circuit density(Jsc)of 1.9 mA cm-2,leading to an encouraging PCE enhancement from 4.59%to 10.23%exceeding the traditional BHJ-PSCs with a PCE of 9.08%.3.Fine-tuning the surface free energy(SFE)of TOPD cathode buffer layer was proposed to achieve a desired perpendicular component distribution for the PBDB-T:ITIC-M photoactive layer.The Owens-Wendt method was adopted to precisely calculate the SFE of TOPD film based on the contact angle measurement.We found that the SFE of TOPD film increases as the annealing temperature rises,and the SFE change causes the vertical component distribution within the bulk region of PBDB-T:ITIC-M.The results of secondary-ion mass spectroscopy visibly demonstrated that the TOPD film with an SFE of 48.71 mJ cm-2(annealed at 90? for 5 min)is beneficial to form desired vertical component distribution.Consequently,compared with conventional bulk heterojunction devices,the PCE increases from 9.00 to 10.20%benefiting from the Jsc increase from 14.76 to 16.88 mA cm-2.