Invited Speech:

High Efficiency Perovskite-based Photovoltaic Cells Fabricated on TiO₂ Nanorod/FTO Substrates

Prof. Charles Surya Clarea Au Endowed Professor in Energy Department of Electronic and Information Engineering The Hong Kong Polytechnic University

Date: 13 Dec 2016 (Tue)
Time: 2:30 - 3:00pm
Venue: TY Wong Hall, 5/F, Ho Sin Hang Engineering Building, CUHK

Abstract:

The dramatic enhancements in the power conversion efficiencies (PCEs) of the perovskite-based solar cells (PSCs) have taken the PV research world by storm. Recent certified result had demonstrated a PCE of 22.1% which is even more impressive considering such excellent result is achieved within just a few years from the initial demonstration of this class of device. Incorporation of nanorods in the device has been touted as an effective technique for enhancing the performance of photovoltaic cells. In this talk we will present recent work by our group on the fabrication and characterization of nanorod PSCs.

Highly aligned TiO2 nanorod arrays were fabricated directly of FTO/glass substrates by solvothermal technique using a modified ketone-HCl system. Deionized water was mixed with concentrated HCl (38% by weight) to reach a total volume of 60 mL. The mixture was stirred under ambient conditions for 5 min before the addition of 1 mL of titanium butoxide (97% Aldrich) in a Teflon-lined stainless steel autoclave. After stirring for another 5 min, an FTO substrate was immersed in the solution. The hydrothermal synthesis was conducted at 180°C for 45 min in an electric oven. After synthesis, the autoclave was cooled to room temperature. The substrate was taken out, rinsed with deionized water and allowed to dry in ambient air. Figure 1 shows a typical sample in which TiO2 nanorods were grown directly on an FTO substrate without any compact TiO2 layer.

Fig. 1 Highly aligned TiO2 nanorods grown directly on FTO subsrtrate.

Methylammonium lead tri-iodide (MAPI) thin films were grown on the TiO2 nanorods/FTO substrates by solution technique followed by thermal annealing at ~100°C. Photovoltaic measurements indicated that efficient nanorod-structured PSCs can be achieved with highly oriented nanorods of approximately 200 – 300 nm long and the optimal thickness of the perovskite layer is around 500 nm. The I-V characteristics of the champion device is shown in Fig. 2 below

Fig. 2 I-V characteristics of the champion device.

The result indicates a PCE >19% with negligible hysteresis. It is noteworthy that high fill factor is achieved despite using a thick perovskite layer. This is attributed to effective carrier extraction by the TiO2 nanorods. Detailed characterizations of the optoelectronic properties as well as the operation mechanism of the device will be presented.

About speaker:

Professor Surya received his PhD degree in Electrical Engineering from the University of Rochester. He had been affiliated with the Electronic and Information Engineering Department of the Hong Kong Polytechnic University (PolyU) for the past 20+ years. Professor Surya had conducted extensive investigations of semiconductor materials and devices for applications in optoelectronics including the application of organic-inorganic perovskite materials in photovoltaics. From 2007 to 2010, Dr Surya served as the Associate Dean of Engineering and later (2010 – 2012) as the Acting Dean of the Faculty of Engineering of PolyU. Since 2013, Dr Surya was appointed as the Clarea Au Endowed Professor in Energy. Professor Surya had been active in EDS and served in various capacities including conference co-chair and chapter chair in the past. Presently Professor Surya is serving as the editor of IEEE Transactions of Electron Devices and IEEE Journal of Electron Devices Society as well as the Chairman of the Optoelectronic Devices Technical Committee.