Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%

Abstract

Perovskite solar cells (PSC) with efficiencies > 20% have only been realized with highly expensive archetype organic hole transporting materials that can impede the large-scale deployment of PSC. Here we demonstrate PSCs achieving stabilized efficiencies of 20.3% with CuSCN as hole electron extraction layer. We developed a new method for the solution deposition of compact and highly conformal CuSCN layers that afford fast carrier extraction and collection. We also show that the notorious instability of CuSCN based PSCs is not associated with the CuSCN/perovskite interface but rather originates from the CuSCN/Au contact. By introducing a thin spacer layer between CuSCN and gold layers, the PSCs retained >95% of their initial efficiency after aging for 500 h under full-sun illumination at 60 °C, and >85% of their initial efficiency after aging at 85 °C for 1000 h. Importantly, under both continuous illumination and thermal stress, CuSCN based devices surpass the stability of spiro-OMeTAD based PSCs.One Sentence Summary: A record performance displayed by operationally stable perovskite solar cells employing all-inorganic charge extraction layers was realized after introducing a simple dynamic approach for the deposition of thin and conformal CuSCN layer onto perovskite layer and a thin spacer layer between CuSCN and gold layers, which will foster their large scale deployment.The prominence of organic-inorganic perovskite solar cells (PSC) can be credited to the unprecedented advancement in the power conversion efficiencies (PCEs), realized mostly by tailoring the formation and composition of the absorber layer (1,2). Certified PCEs >20% have been obtained while retaining the electron selective TiO 2 layer and by using either spiroOMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene] or a polymerbased PTTA (poly-triarylamine) as the hole-transporting material (HTM) (2,3). However, the cost of these HTMs is prohibitively high for large-scale applications and the long-term operational and thermal instability seems to be associated with the archetype organic HTMs or their ingredients (4). One of the strategies to combat the issues of cost and instability could be the use of inexpensive inorganic hole extraction layers similar to the use of TiO 2 as an electron transporting material (5). However, obtaining stable PCEs >20% with PSCs using inorganic 2 HTMs, such as NiO, CuI, Cs 2 SnI 6 , and CuSCN when subjected to light soaking under realistic operational conditions, i.e., at maximum power point and 60°C has remained a challenge (6-9).The realization of efficiencies > 20% using PSCs with inorganic HTMs remains undoubtedly a key goal to foster the large-scale deployment of PSC. Among various inorganic hole transporting materials, CuSCN is an extremely cheap, abundant p-type semiconductor, that exhibits high hole mobility, a good thermal stability and a well-aligned work function (10). The CuSCN is intrinsically p-doped and transmits light across the entire visible and near infrared spect...

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