Controlled Redox of Lithium-Ion Endohedral Fullerene for Efficient and Stable Metal Electrode-Free Perovskite Solar Cells

Abstract

High efficiency perovskite solar cells have underpinned the rapid growth of the field. However, their low device stability limits further advancement. Hygroscopic lithium bis(trifluoromethanesulfonyl)imide (Li + TFSI − ) and metal electrode are the main causes of the device instability. In this work, the redox reaction between lithium-ion endohedral fullerenes and 2,2′,7,7′tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobi-fluorene (spiro-MeOTAD) was controlled to optimize the amount of oxidized spiro-MeOTAD and antioxidizing neutral endohedral fullerenes. Application of this mixture to metal-free carbon nanotube (CNT)-laminated perovskite solar cells resulted in 17.2% efficiency with a stability time of more than 1100 h under severe conditions (temperature = 60 °C, humidity = 70%). Such high performance is attributed to the uninhibited charge flow, no metal-ion migration, and the enhanced antioxidizing activity of the devices.

Large‐Diameter Carbon Nanotube Transparent Conductor Overcoming Performance–Yield Tradeoff

“…While AuCl 3 doping is a common method for the p ‐doping of CNT films, Au has been reported to deteriorate the perovskite system and therefore HNO 3 doping was used for the device application. [ 51,52 ] The device PCE increased to 17.4% owing to the enhancement in FF, which resulted from further reduced R S . [ 53 ] The V OC increased as well for the better aligned energy level between the Fermi level of the DWNT electrodes to the PTAA and the perovskite layer.…”

Environmentally Compatible Lead-Free Perovskite Solar Cells and Their Potential as Light Harvesters in Energy Storage Systems

“…In this context, it is important to inhibit the damage caused by spiro-MeOTAD and its components. To this end, carbon nanotube electrodes which are laminated before the application of spiro-MeOTAD can be used [ 11 , 57 , 58 , 59 , 60 ]. Another method is to apply poly(triarylamine) (PTAA), which has yielded relatively high PCEs.…”

“…This value is higher than that of other types of photovoltaics and extremely close to that of monocrystalline silicon solar cells ( Figure 1 A). With rapid and substantial improvements in PSC technology, the intrinsic device instability of PSCs has also been greatly improved to the level of commercialization [ 11 , 12 ]. However, the presence of lead (Pb) in perovskite materials lowers the market value of PSCs, as Pb is perceived to be toxic and detrimental to the environment.…”

Multi-Walled Carbon Nanotube-Assisted Encapsulation Approach for Stable Perovskite Solar Cells

“…Despite the high efficiency of perovskite solar cells (PSCs), insufficient device stability has been the limiting factor in commercialisation. Moreover, the perovskite materials have been reported to degrade easily due to moisture [ 5 ], oxygen [ 6 , 7 ], ultra-violet (UV) light, trapped charge [ 8 , 9 ], and heat [ 10 , 11 , 12 ]. While most researchers have focused on improving the stability of perovskite materials against moisture, it is noteworthy that good packaging technology can prevent water and oxygen intrusion before degradation occurs in the material [ 13 ].…”