Interface Engineering For Polymer Solar Cells And Perovskite Solar Cells

This work is focused on the investigation of interface engineering for bulk-heterojunction polymer solar cells and planar perovskite solar cells.The dissertation comprises of three main parts.1.The anatase TiO2 nanorods synthesized by a thermal decomposition method were employed as electron transport layers(ETLs)in high-performance inverted bulk-heterojunction(BHJ)polymer solar cells(PSCs)based on the active layers of poly(4,8-bis-alkyloxybenzo(1,2-b:4,5-b')dithiophene-2,6-diyl-alt-(alkyl thieno(3,4-b)thiophene-2-carboxylate)-2,6-diyl)(PBDTTT-C)and(6,6)-phenyl-C71-butyric acid methyl ester(PC71BM).1)TiO2 nanorods with different length-diameter ratio were obtained by extracting low boiling point solvent vapor in the synthesis.Self-assembled TiO2 nanorods ETLs prepared by a solution-phase processing method were characterized by the excellent film morphology,the suitable energy level,and the high electron mobility.2)The power conversion efficiencies(PCEs)of devices with short and long TiO2 nanorods ETLs could achieve 6.96%and 7.26%,respectively,much higher than that using amorphous TiO2 ETLs(6.00%).3)The investigation on the electron transport kinetics indicated that much fewer defects in the interface between TiO2 nanorods ETLs and active layers and within the ETLs reduced the carrier recombination loss,which enhanced the short-circuit current and fill factor,consequently gaining a higher PCE.2.Different kinds of amorphous TOx(TiOx-a)ETLs were utilized in inverted BHJ-PSCs based on PBDTTT-C:PC71BM active layers to gain insight into the light soaking effect.1)The conventional TiOx-a films were prepared by a sol-gel method,and the TiOx-a(UV-air)and TiOx-a(UV-N2)films were obtained through the high-intensitive UV(254 nm)treatment on TiOx-a films in air and N2 atmosphere,respectively.The TiOx-a films were characterized by poor morphology,a certain number of organic functional groups as well as surface hydroxyl groups,and a relatively lower concentration of oxygen vacancy.The TiOx-a(UV-air)films were featured by the better morphology,the most surface hydroxyl groups,and the lowest concentration of oxygen vacancy.While the TiOx-a(UV-N2)films showed the best morphology,the fewest surface hydroxyl groups,and the highest concentration of oxygen vacancy.2)The device with TiOx-a(UV-N2)ETL yielded a PCE of 7.79%,addressed the light soaking effect and improved the stability.But the devices with TiOx-a and TiOx-a(UV-air)ETLs exhibited much lower PCEs,5.98%and 3.27%,respectively,as well as the light soaking effect.3)The investigation on photoelectric properties of devices revealed the light soaking effect was derived from the trapping effect and the interfacial charge accumulation effect in the interface between TiOx ETLs and active layers and within the ETLs.It is believed that changing the species and amount of defects in TiOx films can settle the light soaking effect.3.High-performance planar perovskite solar cells were realized by the utilization of Cs-doped CH3NH3PbI3(MAPbI3(Cs)-NRs)active layers via a two-step deposition method.1)The Cs doping effect in the two-step deposition method could control perovskite grain growth effectively,thus yielding(MA)0.95Cs0.05PbI3 films with improved morphology and producing some nanorods on the surface.While there were not any nanorods on the surface of(MA)0.95Cs0.05Pbl3 films prepared by a one-step deposition method.2)The device based on MAPbl3(Cs)-NRs active layer yielded a PCE of 16.21%,outperforming the one using a pure MAPbI3 layer(12.98%),and meanwhile eliminated the current-voltage hysteresis.3)The investigation on the carrier transport kinetics demonstrated a well hole-transport interface in the device using MAPbI3(Cs)-NRs active layer,inhibiting carrier recombination induced by the charge trapping and ion migration effects,which accordingly contributed to a high PCE.