Determining Out-of-Plane Hole Mobility in CuSCN via the Time-of-Flight Technique To Elucidate Its Function in Perovskite Solar Cells

Abstract
Copper(I) thiocyanate (CuSCN) is a stable, low-cost, solution-processable p-type inorganic semiconductor used in numerous optoelectronic applications. Here, for the first time, we employ the time-of-flight (ToF) technique to measure the out-of-plane hole mobility of CuSCN films, enabled by the deposition of 4 μm-thick films using aerosol-assisted chemical vapor deposition (AACVD). A hole mobility of ∼10–3 cm2/V s was measured with a weak electric field dependence of 0.005 cm/V1/2. Additionally, by measuring several 1.5 μm CuSCN films, we show that the mobility is independent of thickness. To further validate the suitability of our AACVD-prepared 1.5 μm-thick CuSCN film in device applications, we demonstrate its incorporation as a hole transport layer (HTL) in methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs). Our AACVD films result in devices with measured power conversion efficiencies of 10.4%, which compares favorably with devices prepared using spin-coated CuSCN HTLs (12.6%), despite the AACVD HTLs being an order of magnitude thicker than their spin-coated analogues. Improved reproducibility and decreased hysteresis were observed, owing to a combination of excellent film quality, high charge-carrier mobility, and favorable interface energetics. In addition to providing a fundamental insight into charge-carrier mobility in CuSCN, our work highlights the AACVD methodology as a scalable, versatile tool suitable for film deposition for use in optoelectronic devices.

Citation
Mohan, L., Ratnasingham, S. R., Panidi, J., Daboczi, M., Kim, J.-S., Anthopoulos, T. D., … Kreouzis, T. (2021). Determining Out-of-Plane Hole Mobility in CuSCN via the Time-of-Flight Technique To Elucidate Its Function in Perovskite Solar Cells. ACS Applied Materials & Interfaces. doi:10.1021/acsami.1c09750

Acknowledgements
The authors acknowledge EPSRC Centre for Doctoral Training in Plastic Electronic Materials EP/L016702/1 for their support. T.K. wishes to acknowledge STFC (ST/V000039/1) for financial support.

Publisher
American Chemical Society (ACS)

Journal
ACS Applied Materials & Interfaces

DOI
10.1021/acsami.1c09750

Additional Links
https://pubs.acs.org/doi/10.1021/acsami.1c09750

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