CuI and CuSCN as Hole Transport Materials for Perovskite Solar Cells
Authors: Madhavan Vinod , Baloch Ahmer Ali Bozdar , Manekkathodi Afsal , Thirunvukkaarasu Dhanasekaran , Zimmermann Iwan , Roldán-Carmona Cristina , Grancini Giulia , Buffiere Marie , Nazeeruddin Mohammad Khaja , Belaidi Abdelhak , Tabet Nouar 
Published: June 2019

CuI and CuSCN as Hole Transport Materials for Perovskite Solar Cells Vinod E. Madhavan1*, Ahmer Ali
Bozdar Baloch1, Afsal Manekkathodi1, Dhanasekaran Thirunvukkaarasu1, I. Zimmermann2, C. Roldán-
Carmona2, G. Grancini2, M. Buffiere1, Mohammad Khaja Nazeeruddin2, A. Belaidi1 and Nouar Tabet1 1
Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, P. O.
Box 5825, Doha, Qatar 2 Group for Molecular Engineering of Functional Materials, Institute of Chemical
Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, CH-1951 Sion, Switzerland
*vmadhavan@qf.org.qa. ABSTRACT: Perovskite based solar cell is an important area of research for solar energy harvesting and for green energy revolution. The materials used for a thin film solar cell are considerably less with respect to the prevailing silicon based solar cells. There is an interest in copper based inorganic materials, especially copper iodide (CuI) and copper thiocyanate (CuSCN) as hole transport materials (HTMs) in perovskite solar cells (PSCs) for efficient, inexpensive and stable energy harvesting. Copper based films exhibit higher conductivity and wider-band-gap. The existing organic HTMs are expensive and have low hole mobility. The reported high power conversion efficiency (PCE) of CuI and CuSCN based perovskite solar cells are 6% and 20.3% respectively [Christians et al. J. Am. Chem. Soc., 2014, N Arora et al. Science 2017]. The perovskite solar cells based on inorganic CuI and CuSCN can be more stable and cost-effective with respect to spiro-OMeTAD HTM. We present our work on mixed perovskite in the form of (FAPbI3)0.85(MAPbBr3)0.15 in combination with CuI and CuSCN HTMs that lead to efficiencies 5.16% and 15.43% respectively in an n-i-p architecture under full sun illumination. The CuI based device displayed a short-circuit current density (Jsc) of 8.98 mA/cm2, Voc of 898.57 mV and fill factor (FF) of 0.64. Under similar conditions, the device with CuSCN, showed a significant increase in the Jsc (8.95 mA/cm2 to 20.86 mA/cm2) and Voc (from 898.57 mV to 1060 mV) (Figure1). A reference cell with standard spiro-OMeTAD HTM showed a PCE of 19.65% (with Voc of 1180 mV and Jsc of 22.70 mA/cm2). The high Jsc when using CuSCN with respect to CuI is mainly due to the effective charge extraction between the perovskite and CuSCN. However there is a strong quenching in the photoluminescence measurements in both CuI and CuSCN cases, which suggests that excellent hole injection is taking place from the perovskite active layer into the CuI and CuSCN hole transport materials (Figure 2). It is worth noting that CuI based perovskite devices showed a PCE of 6% with excellent photocurrent stability and 2 orders higher electrical conductivity that lead to higher fill factors [Christians et al. J. Am. Chem. Soc., 2014]. Impedance spectroscopy measurements revealed high recombination rate in CuI devices [Huangfu et al, Applied Surface Science 2015]. This could explain the low Voc and Jsc despite the quenching of the photoluminescence spectrum in the presence of CuI and CuSCN. Further studies are in progress in-order to find out the origin of the recombination and how to remediate them. Various device structure models (p-i-n and n-i-p geometry) with copper based HTMs are simulated with SCAPS software to find out the efficient structures with minimum losses. The results shows that the CuSCN based cells are more promising and can be used to prepare high efficiency perovskite solar cells. References J.A. Christians, R.CM. Fung, P.V. Kamat, J. Am. Chem. Soc. 2014, 136, 2, 758–764 pp. N. Arora, M. I. Dar, A. Hinderhofer, N. Pellet, F. Schreiber, S.M. Zakeeruddin, M. Grätzel, Science 2017,10.1126/science.aam5655. M. Huangfu, Y. Shen, G. Zhu, K. Xu and M. Cao*,F. Gu and L. Wang, Appl. Surf. Sci. 2015, 357-B, 2234–2240pp.