Recently, a hole-transport-layer (HTL)-free structure was proposed to decrease the cost of organic lead halide perovskite solar cell (PSC) fabrication. In HTL-free PSCs, instead of using an HTL insertion, the HTL material can be added directly into a perovskite precursor solution to improve hole transport. For example, copper thiocyanate (CuSCN) is used for p-type doping of methylammonium lead triiodide (MAPI) via spin coating from a mixed solution. However, the optimum annealing temperature for CuSCN-doped MAPI (CuSCN:MAPI) PSCs is lower than the 100 °C that is typical for undoped MAPI PSCs. In this study, the origin of such lower annealing temperatures of CuSCN:MAPI PSCs is investigated. The highest power conversion efficiency (PCE) and enhanced electron transport in CuSCN:MAPI are obtained with annealing at 60 °C. Using transmission electron microscopy-energy-dispersive X-ray spectroscopy, it is revealed that annealing at 60 °C results in the uniform distribution of CuSCN, while the annealing at 100 °C induces the aggregation of CuSCN with a diameter of ~20 nm. A large energy barrier formed by the shallow-lying conduction band minimum of these CuSCN clusters hinders electron transport. The lower PCE of CuSCN:MAPI PSCs with annealing at 100 °C is attributed to this deterioration in the electron transport.
Bibliographical noteFunding Information:
This study was supported by the National Research Foundation of Korea [ NRF-2020R1A2C2014644 , 2017R1A5A1014862 (SRC program: vdWMRC center), 2018R1D1A1B07051050 , and 2018R1A6A1A03025582 ]; Samsung Display Company; and Industry-Academy joint research program between Samsung Electronics and Yonsei University.
© 2020 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Materials Chemistry
- Electrical and Electronic Engineering