Abstract
Perovskite solar cells (PSCs) have attracted immense attention since they first came to light in 2010. They have demonstrated extraordinary performance, with efficiencies increasing from 3.8 % to > 25 %, in a short space of time. The success of PSCs can be related to their excellent optoelectronic properties and facile, low-cost fabrication processes. However, the main issue preventing the widespread use of perovskite devices is their instability to air and moisture. The all-inorganic CsPbBr3 perovskite, possesses features that make it considerably more stable than then commonly used perovskite absorber materials, which often contain organic cations. Furthermore, CsPbBr3 has a large band gap (2.3 V) thus only visible light with a wavelength of ≈ 530 nm or higher can be absorbed and used to generate charge carriers. Consequently, the Power Conversion Efficiency (PCEs that) can be achieved by CsPbBr3 based PSCs are significantly lower than the leading PSC devices in the field; the top CsPbBr3 devices have reached efficiencies of ≈ 11 %.Whilst the large band gap of CsPbBr3 renders these devices less suitable for direct light to energy conversion, it bestows them with other useful properties, such as being able to achieve high VOC values (> 1.4 V) using carbon based CsPbBr3 devices. This is greater than the required thermodynamic potential for water oxidation of 1.23 V. This offers CsPbBr3 PSCs applications as photoanodes for water splitting. Consequently, this paves the way for PSCs to potentially be used to produce solar fuels such as hydrogen gas. Previously, CsPbBr3 based PSCs have been encapsulated using a commercially available Graphite Sheet (GS), functionalised with an iridium-based water oxidation catalyst (WOC) on the surface. Whilst CsPbBr3 has increased air and heat stability, it is still unstable to moisture and will degrade when exposed to water. Thus, operating CsPbBr3 based photoanodes for water oxidation, in direct contact with water, remains a challenge.
Expanding on previous work, three strategies for the improvement ofTiO2|CsPbBr3|Carbon|GSWOC photoanodes were identified: i) Improving the VOC of the planar CsPbBr3 devices used, to increase the photovoltage and reduce the amount of external bias required for water oxidation to occur. ii) Increasing the WOC loading on the surface of the GS to help increase the amount of water oxidation and thus the photocurrent produced. iii) Improving the encapsulation of the CsPbBr3 photoanode to extend the lifetime of the device in aqueous conditions.
Overall, the methods used for increasing the concentration of the WOC on the surface of the GS appeared unsuccessful. However, the open circuit voltage of the planar carbon devices was improved to values often > 1.45 V. Furthermore, using an electrochemical flow-based system the lifetime of the device was successfully extended to over 550 h under operating conditions, which may be a record for the lifetime of a lead halide perovskite photoelectrode in direct contact with an aqueous solution under illumination
| Date of Award | 28 Jun 2023 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Petra Cameron (Supervisor) & Andrew Johnson (Supervisor) |