Performance Improvements Of Polymer And Perovskite Solar Cells Through The Hole Transportation Engineering

The power conversion efficiency(PCE)of Polymer solar cells(PSCs)and Perovskite solar cell(Pv-SCs)was mainly affected by the hole transportation.The hole transportation directly determined whether the free hole which was formed by the exciton separation can be collected quickly by the anode,and then the exciton or charge carrier recombination can be reduced.In this paper,we investigated the effects and mechanism of hole transportation on the performance of PSCs and Pv-SCs via the four kind of the hole transport modification.And then we used PTB7:PC71BM as active layer for PSCs and applied CH3NH3PbX3 as absorption layer for Pv-SCs.In order to enhance the hole transportation in PSCs based on PTB7:PC71BM,first of all,the blended active layers of PTB7:PC71BM with DIO were fabricated to regulate the distribution of PTB7 and PC71BM in the vertical stratifcation of the active layer for increasing the hole current density.This result was comfirmed by testing the hole mobility of PSCs.Furthermore,in order to enhance the hole transportation of hole transport layer(HTL)in PSCs based on PTB7:PC71BM,the 2-propanol(IPA)-doped poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate)(IPA-doped PEDOT:PSS)was used to increasing the hole conductivity of the HTL.The enhancement of IPA-doped PEDOT:PSS is mainly shown as the following:(1)the conductivity of HTL increasing from 9.5×10-4 to 2.63×10-3 s/cm;(2)The decreased roughness of IPA-doped PEDOT:PSS likely is good for the contact between the HTL and the active layer,improving the transportation rate;(3)the hole current density enhancing due to the inducing of the IPA-doped PEDOT:PSS.For device fabricated with IPA-doped PEDOTT:PSS and DIO,it has been observed that the short circuit current density(Jsc)increases from 14.48 mA/cm2 to 16.53 mA/cm2,while the fill factor(FF)increases from 67.6%to 73.1%.As the result,the PCE of PSCs increases from 7.24%to 9.06%,which demonstrates 25%improvement,along with good stability.Then,the DMSO-doped PEDOT:PSS was used to increase the hole conductivity for Pv-SCs.We also demonstrated the highly conductive thin DMSO-doped PEDOT:PSS layers significantly enhanced PCE and stability of Pv-SCs.Both imaging and X-ray analysis revealed that the perovskite films grown on DMSO-doped PEDOT:PSS exhibited larger grains with increased crystallinity and much closer crystal plate.The perovskite films grown on DMSO-doped PEDOT:PSS displayed the decreased roughness from 11.2 to 6.2 nm and the enlarge grain size from 160 nm to 190 nm.What's more,the conductivity DMSO-doped PEDOT:PSS was increased and the interface impedance between DMSO-doped PEDOT:PSS and electrode was decreased.Together,these improvements resulted in a 37%boost in the PCE compared to standard P-I-N photovoltaics with pristine PEDOT:PSS.Furthermore,we demonstrated that DMSO-doped PEDOT:PSS devices possess enhanced PCE durability over time.In order to increase the Open Cricuit Voltage(Voc)in Pv-SCs with PEDOT:PSS,we strategically blended poly(2-ethyl-2-oxazoline)(PEOz)with PEDOT:PSS(PEOz-PEDOT:PSS)as a modified HTL for high-performance Pv-SCs.The PEOz-PEDOT:PSS HTL exhibited enhanced features over the conventional layer including the following:(1)promoting perovskite with enlarged grain sizes,(2)decreasing the recombination of the perovskite film,(3)decreasing the difference of the non-capacitive current densities from forward and reverse in Pv-SCs.Remarkably,by using PEOz-PEDOT:PSS as the HTL,we can achieve a high power conversion efficiency of 17.39%,a increased Voc from 0.96 V to 1.08 V,and very low hysteresis for Pv-SCs,along with good stability.We also shown that the PEOz-PEDOT:PSS HTL films can be broadly applied to polymer solar cell systems where the PCEs of PTB7:PC7iBM solar cells increase from 7.80%to 8.78%.These demonstrations displayed that solution processed PEOz-PEDOT:PSS HTL films could have a wide range of applicability in different solar cell types and possibly other electronic systems.Finally,to reduce the hole trap-state density and the carrier recombination in the perovskite film,here we demonstrated that a a simple yet valuable additive dripping(AD)treatment step using Chlorobenzene(CB)doped with diphenyl ether(DPE)towards controlling the crystallization and morphology of perovskite film.The perovskite film with AD treatment displayed enhanced features over the perovskite film without AD treatment including the following:(1)reducing the hole trap-state density from 1,37 ×1016cm-3 to 9.07x1015 cm-3;(2)having the bule shift of perovskite PL peak from 777nm to 771nm,which indicated the recombination in the perovskite film was restrained;(3)effective charge transfer from the perovskite film to the HTL.Together,the advantages can significantly improve the PCE by 15%up to 16.64%with a high Jsc of 22.67 mA/cm2,compared to the control device using CB.The benefit came from the perovskite film with the enlarge grain size and the increased crystalline.We suggested that these unique attributes can reduce the hysteresis problem typical of Pv-SCs.These results shown that the AD approach is a promising technique for improving Pv-SCs.In summary,the influence of different treatment strategy for the hole trasportation on the PSCs and Pv-SCs performance has been studied,including additives,solvent doped into HTL,polymer doped into HTL and additive dripping which laid a solid foundation for the realization of the high efficiency solar cells with the good stability.