Shuaifeng Hu

Abstract:

Vacuum-based deposition is a scalable, solvent-free industrial method ideal for uniform coatings on complex substrates. However, all vacuum-deposited perovskite solar cells fabricated by thermal evaporation trail solution-processed counterparts in efficiency and stability due to film quality challenges, necessitating advancement and improved understanding. Here, we report a co-evaporation route for 1.67-eV wide-bandgap perovskites by introducing a PbCl2 co-source to optimize film quality. We promote perovskite formation with pronounced (100) “face-up” orientation and deliver a certified all vacuum-deposited solar cell with 18.35% efficiency (19.3% in the lab) for 0.25-cm2 devices (18.5% for 1-cm2 cells). These cells retain 80% of peak efficiency after 1,080 hours under the ISOS-L-2 protocol. Leveraging operando hyperspectral imaging, we provide spatiotemporal spectral insight into halide segregation and trap-mediated recombination, correlating microscopic luminescence features with macroscopic device performance while distinguishing radiative from non-ideal recombination channels. We further demonstrate 27.2%-efficient 1-cm2 evaporated perovskite-on-silicon tandems and outdoor stability of all vacuum-deposited tandems in Italy, retaining ~80% initial performance after 8 months.

Abstract:

<jats:p>This study pioneers a solvent-additive cascade strategy to achieve crystallographically homogenous perovskite films, breaking the efficiency–stability trade-off by harnessing facet-dependent properties for record performance.</jats:p>

Abstract:

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.

Abstract:

Thanks to their superior bandgap tunability and high absorption coefficient, metal halide perovskites demonstrate high potential for fabricating multijunction photovoltaics capable of achieving power conversion efficiencies surpassing the radiative efficiency limit of single-junction solar cells[1],[2]. One of the key challenges currently facing all-perovskite multijunction photovoltaics is the low quality of the narrow bandgap (~1.25 eV) mixed tin-lead perovskite films used as the rear absorber. At this conference, we will present our recent investigations on the mixed tin−lead perovskites covering the control of the Sn(II) oxidation[3], interface carrier extraction[4], and in-situ surface reaction[5], as well as the understanding of the solution chemistry and resultant crystallization[6], aiming to generate a global picture toward the comprehensive understanding of this material and its photovoltaic devices. As a result, we have obtained efficiencies of over 23.9% for the single-junction tin−lead perovskite devices, with an open circuit voltage of up to 0.91 V. Building on optimizations of neat lead perovskites, we then showcase the successful integration of these improved mixed tin-lead perovskites into double-, triple-, and quadruple-junction tandem solar cells, achieving efficiencies exceeding 29%, 28%, and 27%, respectively. In addition, we will propose promising strategies for enhancing the light and temperature stability of the involved perovskite subcells, aiming to improve the reliability of efficient all-perovskite multijunction photovoltaics. Furthermore, we will also share insights and recent progress achieved in perovskite-on-silicon multijunction cells.