Prof Henry Snaith FRS

Abstract:

Semi-transparent perovskite solar cells (ST-PSCs) have shown great potential in building-integrated photovoltaics. However, the performance of ST-PSCs is still far from achieving their true potential. Herein, a functional additive, [4-(trifluoromethyl)phenyl] sulfonyl chloride (TFBSC), is incorporated into the perovskite precursor solution to regulate the crystallization process and reduce defects in the perovskite films. The addition of TFBSC improves the perovskite film morphology and increases the charge carrier lifetime and photoluminescence quantum efficiency, compared with the control perovskite films. As a result, the champion device modified with TFBSC shows a power conversion efficiency (PCE) of 14.75% with a light utilization efficiency (LUE) of 3.92%, whereas the control device shows PCE and LUE values of 10.71% and 2.96%, respectively. Moreover, the unencapsulated TFBSC-modified device retains ∼90% of its initial PCE after 1500 h of storage under ambient conditions (relative humidity of ∼30%–40%). These findings could provide new avenues to develop high performance ST-PSCs for smart building applications.

Abstract:

Monolithic perovskite–organic tandem solar cells (POTSCs) have attracted considerable attention in recent years due to their compatible fabrication routes and advances in single-cell efficiencies. To further boost the performance of POTSCs, reducing the voltage losses that mainly arise from wide bandgap (WBG, >1.7 eV) perovskite subcells and interconnecting layers (ICLs) is critical. Here, a new ICL with a configuration of C60/YbO x /Au/MoO x is demonstrated for constructing the monolithic POTSC. The YbO x -based ICL benefits from an ohmic contact and high transparency, resulting in improved POSTC performance. The champion device presents a PCE of 23.2% owing to a high V OC of 2.11 V (approximately equal to the sum of individual V OC’s of the subcells) without compromising the short-circuit current density and fill factors. This work opens an avenue for developing efficient ICLs in POTSCs.

Abstract:

Metal halide perovskites could form the basis of future display technology due to their powerful optical properties. However, the commercialization of electroluminescent perovskites has been hindered by key challenges, including limited operational lifetime and instability in blue emission. Here we highlight the potential of perovskites in colour conversion displays. We examine the particular advantages of perovskite materials as colour conversion layers: narrow emission spectrum, high absorption coefficients, high-brightness operation, photon recycling and ease of manufacturing. We provide a framework for the development of RoHS (Restriction of Hazardous Substances)-compliant and colour-filter-free perovskite-based colour conversion displays and offer guidelines for commercialization. We also explore the potential of using perovskite colour conversion layers to create advanced augmented reality and virtual reality technologies.

Abstract:

Tin-halide perovskites currently offer the best photovoltaic performance of lead-free metal-halide semiconductors. However, their transport properties are mostly dominated by holes, owing to ubiquitous self-doping. Here we demonstrate a noncontact, optical spectroscopic method to determine the effective mass of the dominant hole species in FASnI3, by investigating a series of thin films with hole densities finely tuned through either SnF2 additive concentration or controlled exposure to air. We accurately determine the plasma frequency from mid-infrared reflectance spectra by modeling changes in the vibrational response of the FA cation as the plasma edge shifts through the molecular resonance. Our approach yields a hole effective mass of 0.28m e for FASnI3 and demonstrates parabolicity within ∼100 meV of the valence band edge. An absence of Fano contributions further highlights insignificant coupling between the hole plasma and FA cation. Overall, this approach enables noncontact screening of thin-film materials for optimized charge-carrier transport properties.

Abstract:

The properties of metal‐centred species in metal halide perovskite precursor solutions substantially influence the formation and evolution of colloidal particles, which in turn dictate the crystallisation process and the film quality. In this work, we assess the “hard” and “soft” Lewis acid characteristics of Sn2+ and Pb2+ cations as a strategy to modulate the chemical environment of these metal‐containing species in mixed‐metal tin–lead perovskite precursor solutions. We observe enhanced simultaneous access to both metal centres upon adding compounds with functional groups suggested by the hard–soft acid–base principle. Theoretical calculations suggest that the hard base carboxyl group preferentially interacts with Sn2+‐based species, while the softer base thiol group also targets Pb2+‐based species. By effectively accessing and manipulating possible classes of inorganic species and their colloidal particle properties in the precursor solutions, we achieve 1.26 eV perovskite polycrystalline films exhibiting enhanced structural and optoelectronic quality, giving the best quasi‐Fermi level splitting values of up to 0.95 eV. As a result, the solar cell devices demonstrate efficiency values of up to 23.3% with an extended operational lifetime, retaining 80% of their initial efficiency after over 280 and 180 h of maximum power point tracking under simulated AM1.5G illumination at 25 and 65 °C, respectively.