Researchers from Ulsan National Institute of Science and Technology (UNIST), Gyeongsang National University (GNU) and University of Ulsan explain that in spiro-OMeTAD-based hole-transporting layer (HTL) protocols, 4-tert-butylpyridine (tBP) is an indispensable component; however, its inclusion leads to substantial detrimental effects, hindering thermal stability.
Recently, the team developed a tBP-free spiro-OMeTAD approach by substituting ethylene carbonate (EC) electrolyte for tBP. The electronegative carbonyl functionality led to the formation of a solvation complex with Li+ ions, addressing the solubility concern of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in chlorobenzene even without tBP.
The liberated TFSI− ions facilitate the stabilization of a larger population of spiro-OMeTAD˙+ radicals, thereby enabling efficient p-doping.
The EC-incorporated HTL achieved a maximum power conversion efficiency (PCE) of 25.56% (certified 25.51%).
In scaled-up applications, perovskite solar mini-modules with aperture areas of 25 and 100 cm2 demonstrated PCEs of 23.22% and 22.14%, respectively.
The elevated glass transition temperature and robustly sequestered Li+ ions endow the devices with resilience against damp-heat conditions (85 °C/85% RH) for 1000 hours.
This work could enable a step towards commercialization by addressing thermal stability issues.
