Prof Henry Snaith FRS

Abstract:

We report the synthesis and the optoelectronic characterization of three new 4H-pyran-4-ylidene and thiazole derivatives (pyt) as metal-free organic dyes for solid-state dye-sensitized solar cells (DSSCs). We investigate the performance and the long-term stability of devices employing pyt dyes functionalized with carboxylic and phosphonic acids as TiO2 anchoring groups. In contrast to reports on liquid electrolyte DSSCs, we show that solid-state DSSCs prepared with phosphoric pyt derivatives can achieve similar power conversion efficiency to their carboxyl analogues. We make use of the Mott-Schottky analysis and equivalent circuit models to demonstrate that a phosphonic group induces a significant increase in built-in voltage at the TiO2-hole transporter interface, which results in a higher open circuit voltage.

Abstract:

Organic-inorganic halide perovskite solar cells have rapidly evolved over the last 3 years. There are still a number of issues and open questions related to the perovskite material, such as the phenomenon of anomalous hysteresis in current-voltage characteristics and long-term stability of the devices. In this work, we focus on the electron selective contact in the perovskite solar cells and physical processes occurring at that heterojunction. We developed efficient devices by replacing the commonly employed TiO2 compact layer with fullerene C60 in a regular n-i-p architecture. Detailed spectroscopic characterization allows us to present further insight into the nature of photocurrent hysteresis and charge extraction limitations arising at the n-type contact in a standard device. Furthermore, we show preliminary stability data of perovskite solar cells under working conditions, suggesting that an n-type organic charge collection layer can increase the long-term performance.