Nanostructred Hybrids Interlayer For Polymer Solar Cells And Indium Free Perovskite Solar Cells

Polymer solar cells(PSCs)have attracted enormous attention as the most promising source of green energy for the future due to the superior advantages of lightweight,low price,solution-based processing,mechanical flexibility and large area roll-to-roll manufacturing at low temperature.In recent years,the power conversion efficiency(PCE)of PSCs has been dramatically improved and already reached over 12% for single stack devices.Various mathods have been applied to improve the performance of PSCs.In this paper,our work focuses on the modification of the buffer layer,as well as the interfacial compatibility and energy alignment between active layer and buffer layer,aiming to increase charge selective,reduce the recombination of carriers,increase the electron mobility and obtain efficient PSCs and indium free perovskite solar cell.The flexible inverted polymer solar cells composed of poly(3-hexylthiophene)(P3HT):(6,6)-phenyl-C61 butyric acid methyl ester(PC61BM)blends on the flexible poly(ethylene terephthalate)(PET)substrates were fabricated,which showed improving device performance by using solution-processed ZnO/poly(ethylene glycol)(PEG)hybrids as electron transport layers compared to the devices using the pristine ZnO as electron transport layers.It is mainly attributed to the effective passivation of the ZnO surface traps,suppression of the interfacial charge recombination,decrease of the work function and improvement of the energy-level alignment between ZnO and PC61 BM.PEG with different molecular weight have diferent effect on the ZnO.It was found that the short PEG backbone(eg.Mw = 400)containing less oxygen could not effectively passivate ZnO surface traps,meanwhile,longer PEG backbone(eg.Mw = 20000)could lead to the formation of the charge transport barrier owning to the insulating nature of PEG.Furthermore,solar cells with the ZnO/PEG buffer also showed better air-stability compared to the devices with the pristine ZnO buffer.In addition,due to the simplicity and low-temperature process,the ZnO/PEG hybrids can be well suitable as cathode buffer for large area roll-to-roll manufacturing of printed polymer solar cells.A novel ZnO@reduced graphene oxide-poly(N-vinyl pyrrolidone)(ZnO@RGO-PVP)nanocomposite by in situ growth of ZnO nanoparticles in poly(N-vinyl pyrrolidone)decorated reduced graphene oxide(RGO-PVP)has been developed as electron transport layer for improving polymer solar cells performance.PVP not only can favor homogeneous distribution of the RGO via the strong ?-? interactions between graphene and PVP molecules,but also can act as a stabilizer and bridge to control the in situ growth of sol-gel-derived ZnO nanoparticles on surface of the graphene.At the same time,RGO provides a conductive connection for independently dispersion of ZnO nanoparticles to form uniform nanoclusters with reduced domain boundaries and surface traps.Moreover,ZnO@RGO-PVP produces a better energy alignment.Compared to the bare ZnO,ZnO@RGO-PVP electron transport layer substantially reduces the recombination of carriers,increases the electrical conductivity and enhances electron extraction.Consequently,the performance of the inverted device based on thieno[3,4-b]-thiophene/ benzodithiophene(PTB7)?[6,6]-phenyl C71-butyric acid methyl ester(PC71BM)with ZnO@RGO-PVP as electron transport layer has been greatly improved to 7.5% with improved long-term stability.The results reveal that ZnO@RGO-PVP is universally applicable as an electron transport layer for improving polymer solar cells performance.Amphiphilic fullerene-end-capped poly(ethylene glycol)(C60-PEG)is synthesized to modify uniform Zn O arrayed nanorods(ANs)grown in situ on the surface of poly(N-vinyl pyrrolidone)decorated reduced graphene oxide(RGO).The two dimensional(2D)graphene provides a stable and conductive flat substrate for one dimensional(1D)arrayed nanorods with reduced defects.The addition of amphiphilic C60-PEG can improve the compatibility of electron transport layer and the active layer.Meanwhile,C60-PEG produces a modified efficacy on the arrayed nanorods with reduced defects and decreased work function.Compared to the bare ZnO ANs,C60-PEG modified ZnO ANs@RGO electron transport layer can reduce the recombination of carriers,increase the electron mobility and enhance electron extraction.As a result,the efficiency of the inverted polymer solar cells based on PTB7?PC71BM is improved to 8.1% with better long-term stability.C60-PEG was applied as electron transport layer alone or as a self-assembled monolayer to modify ZnO,improving the performance of inverted polymer solar cells.At the same time,two types of novel fullerene derivative/ZnO hybrids were prepared by physical blending C60-PEG with ZnO nanocrystals(ZnO/C60-PEG)and by in situ growth ZnO from C60-PEG(ZnO@C60-PEG)at relatively low temperature.C60-PEG can tune energy level alignment and improve the interfacial compatibility between active layer and interfacial layer.Besides,for two hybrids,the C60-PEG could be beneficial for the dispersion of ZnO and produce n-doping effect on the ZnO,which results in decreased conduction band,reduced carrier recombination and improved extraction and collection of electron.Compared with the ZnO/C60-PEG by physical blend approach,the ZnO@C60-PEG by growth approach showed more favorable morphology and higher electron mobility by developing a homogenous network.Consequently,inverted polymer solar cells based on PTB7:PC71BM present a PCE of 6.6% by incorporating C60-PEG into as electron transport layer.Moreover,an improved PCE of 7.4% with good long-term stability in air were further achieved by using C60-PEG modified ZnO interlayer.The efficiency of the inverted polymer solar cells based on PTB7?PC71BM is raised to 8.0% for ZnO@C60-PEG electron transport layer and to 7.5% for ZnO/C60-PEG electron transport layer with improved long-term stability.In this work,C60-PEG could be prepared by solution process at room temperature without additional annealing,which shows the potential in large-scale printed polymer solar cells.ZnO,plasmonic gold nanoparticles and conductive carbon nanotubes were combined by in situ growing to improve the light absorption and the electron mobility and the performance of polymer solar cells.Gold nanoparticles decorated carboxylic CNT(CNT-Au)was prepared by simple dehydration-condensation reaction.While CNT provides the template for the in situ growth of ZnO to form homogeneous film with less defects and higher conductivity,gold nanoparticles induce the surface plasmon effect to increase the light absorption.Compared to the bare ZnO,ZnO@CNT-Au nanohybrids could increase photo-generated excitons,decrease the charge recombination and facilitate the electron collection.In consequence,the power conversion efficiency of inverted polymer solar cell based on PTB7:PC71BM was improved to 7.9% by adopting ZnO@CNT-Au as electron transport layer.We have demonstrated a comparative study of perovskite solar cells based on SnOx electron transport layers.Specifically SnOx prepared by ALD using water,ozone,or oxygen plasma as oxidant has been studied.The best characteristics were achieved for devices based on ozone-SnOx as electron transport layer with a stable PCE of 15.3% and a remarkably high Voc of 1.17 V.Photoelectron spectroscopy revealed the formation of a PbI2 interfacial layer between the SnOx and the perovskite in all devices.Different interface dipoles resulted in different extraction barriers in the CB between the MAPbI3 and the Pb I2 for the SnOx grown with different oxidants.Notably the barrier was the largest in case of H2O-SnOx and the smallest in case of the ozone-SnOx,which resulted in superior electron extraction when ozone-SnOx was used.Based on this insight,we designed an ITO-free semitransparent bottom electrode based on SnOx /Ag /SnOx,in which the SnOx served as electron extraction layer and its outstanding permeation barrier properties efficiently protected the ultra-thin silver layer against corrosion due to halide compounds.The resulting In-free perovskite cells achieve a PCE up to 11%.The low process temperature(< 100°C)of the SnOx /Ag /SnOx electrode provides a clear advantage over ITO,which is typically processed at high temperatures.