Damp-heat stable and efficient perovskite solar cells and mini-modules with a tBP-free hole-transporting layer

Abstract

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. Here, a tBP-free spiro-OMeTAD approach was successfully devised 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. Our findings signify a crucial leap towards commercialization by addressing thermal stability issues.