Elimination of charge carrier trapping in diluted semiconductors

Abstract

In 1962, Mark and Helfrich demonstrated that the current in a semiconductor containing traps is reduced by N/Nt(r), with N the amount of transport sites, Nt the amount of traps and r a number that depends on the trap energy distribution. For r > 1, the possibility opens that trapping effects can be nearly eliminated when N and Nt are simultaneously reduced. Solution-processed conjugated polymers are an excellent model system to test this hypothesis, because they can be easily diluted by blending them with a high-bandgap semiconductor. We demonstrate that in conjugated polymer blends with 10% active semiconductor and 90% high-bandgap host, the typical strong electron trapping can be effectively eliminated. As a result we were able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their efficiency at nearly ten times lower material costs.

Vapor transport deposition of antimony selenide thin film solar cells with 7.6% efficiency

“…This, again, indicates the presence of trap-assisted Shockley–Read–Hall (SRH) recombination in both devices 29, 30 . The slope was decreased from 1.51( k B T/q ) to 1.23( k B T/q ) by using VTD process, suggesting reduced trap-assisted recombination in VTD-fabricated devices 28, 31 . We measured the TA decay of the two devices to investigate the carrier lifetime (Supplementary Fig.…”

Enhanced Hole Transport in Ternary Blend Polymer Solar Cells

“…As summarized in Table 2, the hole mobility in binary blend films was comparable to or larger than that in neat films. [39][40][41] In these diluted blends, the charge transport was improved or comparable to that in neat films. As shown in Figure 7, trap filling region was observed from 0.1 to 1 V for both PTB7-Th and PDCBT neat films but not observed for the ternary blend film.…”

Efficient Blue Polymer Light‐Emitting Diodes with Electron‐Dominated Transport Due to Trap Dilution

“…[13] Figure 2b shows both electron and hole current for a blend of PSF-TAD:PFO at 10:90 wt% ratio. The hole current in the blend is again trap-free space-charge limited, but now the electron current is higher than the hole current and has an identical voltage dependence, indicating that also the electron transport now shows trap-free SCLC behavior, with an electron mobility higher than the hole mobility.…”

“…In our earlier work on poly[2-methoxy-5-(2′-ethylhexyloxy)p-phenylene vinylene] (MEH-PPV) blended with poly(9-vinylcarbazole)(PVK) or PFO, addition of 90% of the wide band gap polymer (ten times dilution) was suffi cient to virtually eliminate trapping effects. [ 13 ] Figure 2 b shows both electron and hole current for a blend of PSF-TAD:PFO at 10:90 wt% ratio. The hole current in the blend is again trap-free space-charge limited, but www.MaterialsViews.com www.advelectronicmat.de (3 of 6) 1500406 wileyonlinelibrary.com now the electron current is higher than the hole current and has an identical voltage dependence, indicating that also the electron transport now shows trap-free SCLC behavior, with an electron mobility higher than the hole mobility.…”