P‐Dopant: LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19% (Adv. Energy Mater. 32/2019)

Abstract

Spiro‐OMeTAD has been widely used as a promising hole conductor for metal halide perovskite solar cells due to its ability to deliver highly efficient devices. However, additives such as lithium salt and O2 exposure are still required to modify the electrical properties due to the poor conductivity of pristine spiro‐OMeTAD. In article number 1901519, Jianfeng Lu, Udo Bach and co‐workers employ the oxidized form of spiro‐OMeTAD as a dopant to improve the efficiency of the spiro‐OMeTAD‐based lithium‐free perovskite solar cells from 10% to 19.3% while simultaneously enhancing the device stability.

Dopant‐Free, Donor–Acceptor‐Type Polymeric Hole‐Transporting Materials for the Perovskite Solar Cells with Power Conversion Efficiencies over 20%

“…Hole‐transporting layers (HTLs) are always required to construct high‐efficiency PVSCs. The most commonly used hole transport material (HTM) in record‐breaking PVSCs is 2,2′,7,7′‐tetrakis‐( N , N ‐di‐ p ‐methoxyphenyl‐amino)‐9,9′‐spirobifluorene (spiro‐OMeTAD) . However, the complex synthetic route, poor film quality, and need for several dopants limit the suitability of spiro‐based small‐molecule HTMs for future large‐scale PVSC applications .…”

Nonhalide Materials for Efficient and Stable Perovskite Solar Cells

“…Apart from metal salts containing TFSI – anion, organic salts possessing TFSI – anion were also developed. [ 38,72 ] A dicationic salt of Spiro‐MeOTAD(TFSI) 2 was employed to dope Spiro‐ MeOTAD. [ 76 ] The doping process was realized via the oxidation of Spiro‐MeOTAD by reduction of Spiro‐MeOTAD 2+ .…”

“…Since the hygroscopic LiTFSI and O 2 can promote the degradation of PSCs, this doping process avoid the participation of O 2 required for the traditional LiTFSI doping process. A higher PCE of 19.3% was achieved based on the device with Spiro‐MeOTAD(TFSI) 2 as compared to the control device doped by LiTFSI (18.1%), [ 38 ] where improved hole extraction was responsible for the enhanced efficiency. Furthermore, better stability was observed for the Spiro‐ MeOTAD(TFSI) 2 doped device than the LiTFSI doped one after ageing under continuous one sun illumination at relative humidity of 40% and 50 °C for 300 h. The LiTFSI‐free organic salts as p‐type dopant was found to be very effective in achieving efficient and stable PSCs.…”

“…It is well known that LiTFSI has been extensively adopted for increasing conductivity of the commonly used hole transport material (2,2',7,7'‐tetrakis ( N , N ‐di‐ p ‐methoxyphenyl‐amine)‐9,9'‐spirobifluorene (Spiro‐MeOTAD) and poly(triarylamine) (PTAA)). In order to overcome the moisture instability of devices resulting from hygroscopic LiTFSI salt, a variety of new dopants containing molecular anions have been developed to take place of traditional LiTFSI, such as AgTFSI, [ 34 ] Zn(TFSI) 2 , [ 12 ] Cu(I/II)(dpm) 2 (PF 6 ) 2 (JQ1), [ 35 ] bis[2,2′‐(chloromethylene)‐dipyridine] copper(II) bis[bis(trifluoromethylsulfonyl) imide] [Cu(bpcm) 2 ], [ 36 ] phosphoric acid (H 3 PO 4 ), [ 37 ] Spiro‐MeOTAD(TFSI) 2 , [ 38 ] etc. Apart from the use in dopants, molecular anions were directly incorporated into CTMs.…”

Gaining Insight into the Effect of Organic Interface Layer on Suppressing Ion Migration Induced Interfacial Degradation in Perovskite Solar Cells

“…For hole‐transporting layer (HTL), several dopant‐free hole‐transporting materials (HTM) or LiTFSI‐free Spiro‐OMeTAD are designed to avoid extrinsic ion migration. [ 29,30 ] 3) Incorporating interface layers: Yang et al. [ 31 ] used capacitance−voltage measurements to investigate the interfacial degradation mechanism and emphasized the importance of tuning the interface between electron‐transporting layer (ETL) and metal electrode, that is, via employing a cathode interface layer (CIL) in inverted PSCs to reduce the interfacial degradation.…”