Influence of PEDOT:PSS Material Characteristics on the Performance of PEDOT:PSS/n-Si Hybrid Heterojunction Solar Cells

Author:Zhu Ju Zuo

Supervisor:ye ji chun


Degree Year:2018





Organic/inorganic hybrid heterojunction solar cells comprised of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)and n type silicon(n-Si)have attracted wide attention due to its simple fabrication and high power conversion efficiency.PEDOT:PSS is a kind of transparent conductive polymers,with high transmittance of over 80%,high conductivity of 700 S/cm and high work function of 5.0 eV.PEDOT:PSS contacts to n-Si inducing inversion layer at the silicon surface,without Fermi energy level pinning effect.The high transmittance and anti-reflective effect of the PEDOT:PSS results in a majority of photons absorbed in the silicon.As well,PEDOT:PSS has excellent passivation effect on the silcon surface leading to high quality of p-n junction.PEDOT:PSS as the hole transport layer,its characteristics has significant influence on the performance of the PEDOT:PSS/n-Si hybrid heterojunction solar cells,and it’s important to enhance the device performance by optimizing the performance of the PEDOT:PSS.In this dissertation,we focus on the PEDOT:PSS material characteristics to improve the photovoltaic performance of the PEDOT:PSS/n-Si hybrid heterojunction solar cells.Primary research works are including as follow:(1)Influence of double-layered PEDOT:PSS on the photoelectric performance of the PEDOT:PSS/n-Si hybrid heterojunction solar cells has been investigated.Double-layered PEDOT:PSS,composed of high work function PEDOT:PSS on bottom and high conductivity PEDOT:PSS on top,were designed to improve the performance of the devices.As a result,the high work function PEDOT:PSS induced the strong inversion layer at the silicon surface,largening the build-in voltage and suppressing the silicon surface recombination.The high work function PEDOT:PSS with 35 nm thickness had no adverse impact on the series resistance of the device after covering the high conductivity PEDOT:PSS layer.After applying double-layered PEDOT:PSS,the open circuit voltage of the device increased to 640 mV by 31 mV,with fill factor of0.755 and power conversion efficiency of 12.69%.The improvement of the open circuit voltage is beneficial to the separation of the photo-generated carriers in the space charge region.The influence of different mass fraction of the ethylene glycol added into the high work function PEDOT:PSS on the morphology and conductivity was investigated as well.With the addition of ethylene glycol from 0 wt%to 10 wt%,the surface roughness of the high work function PEDOT:PSS increased from 0.72 nm to 2.31 nm,and the square resistance decreased from 2?106Ω?sq-1 to 9.9?103Ω?sq-1.The open circuit voltage changed little with the addition of different mass fraction ethylene glycol.The short current density reduced slightly and the fill factor increased with the increasing mass fraction of the ethylene glycol,and the best power conversion efficiency was obtained with the addition of 7 wt%ethylene glycol.(2)Application of the modified metal polymer nanocomposite top electrode in the PEDOT:PSS/n-Si hybrid heterojunction solar cells.Based on the double-layered PEDOT:PSS structure,ultrathin silver electrode was used to replace the top high conductivity PEDOT:PSS layer and the Ag grids to improve the carrier collection efficiently.When the thickness of the Ag film was below 10 nm,the Ag film showed island-like structure if it was directly deposited onto the PEDOT:PSS,resulting in poor optical and electric performance.When introducing an ultrathin Au/MoOx modified layer,a smooth Ag film were obtained with the thickness of 6 nm.The ultrathin Au/MoOx modified layer also reduced the contact resistance between the PEDOT:PSS film and the Ag film,improving the optical and electrical performance significantly.The MoOx with high work function strengthened the inversion layer at the silicon surface,suppressing the surface recombination,and the carriers were separated and collected effeciently.The device with the Au/MoOx modified metal polymer nanocomposite top electrode showed high fill factor of 0.802,demonstrating a promising way to collect the carrier efficiently.For the low short current density of the device with the Au/MoOx modified metal polymer nanocomposite top electrode,we introduced a MoOx film as an antireflection layer on top and calculated the optimum thickness of the PEDOT:PSS and the MoOx by finite-element method.The results showed when the thickness were about 40 nm and 45 nm,respectively,the optical photocurrent loss was minimized.The experiment results showed that the short current density was improved to 23.13 mA?cm-2 with power conversion efficiency of 10.82%,after covering a MoOx antireflection layer.