Abstract
We investigate the effect of the polyelectrolyte lithium poly(styrene sulfonate) (Li:PSS) on the electronic band structure of organic solar cells and find that it functions as a hole transport layer, allowing improved efficiency and device stability.
Highlights
One of the motivations to explore lithium salt of PSS (Li):PSS as an hole transport layer (HTL) material is due to its reduced acidity compared to PEDOT:PSS, which is ubiquitously used in conventional structure organic solar cell (OSC)
We anticipated that the reduced acidity of Li:PSS would prolong the stability of OSCs by eliminating acid-mediated degradation mechanisms which are known to occur at the interface between an HTL and active layer in typical OSCs
It has been reported in the literature[39] that acidic HTLs have a higher work function (WF) at their surfaces than non-acidic HTLs, we observed that the WF values for Li:PSS and all combinations of Li:PSS and PEDOT mixtures were in the range of 4.86 to 4.94 eV, similar, or slightly lower than the value measured for PEDOT:PSS (5.01)
Summary
Increasing interest in organic solar cells has driven remarkable advances in the discovery of new materials and devices with high-performance architectures; a wide array of new HTL and ETL materials have emerged in the past few years and contributed to improvements in device efficiency.[7,8] Compared to the wide variety of ETLs that have been reported, a comparatively limited number of HTL types are known to be effective in conventional structure OSCs.[9]Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PED-OT:PSS) is most often used as an HTL in conventional structure OSCs.[10,11,12] It has several advantages including water solubility, facile solution processability and low-temperature fabrication.[13]. OT:PSS mixtures, their effect on the electronic band structure of OSC devices at the Li:PSS/PTB7 interface and on OSC performance and stability.
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