image: Crystallization process of 2.0 mol L⁻¹ perovskite precursor solutions without (a) and with (b) EGTHCl additive observed under optical microscopy (scale bar: 100 μm). (c) In situ UV-Vis absorption spectra of wet films during annealing, comparing samples without and with EGTHCl. (d) Grazing-incidence X-ray diffraction (GIXRD) analysis showing linear fits of 2θ-sin²ψ for control and EGTHCl-modified perovskite films. (e) Schematic phase evolution of perovskite film formation with and without EGTHCl molecules.
Credit: ©Science China Press
Researchers have proposed an effective and straightforward strategy to overcome the critical performance bottleneck of bifacial perovskite solar cells (Bi-PSCs): photon loss. Unlike traditional single-junction solar cells, Bi-PSCs often use semi-transparent rear electrodes that lack reflective properties, resulting in shortened optical paths and significant photon losses.
To address this issue, the team constructed a high-quality thick perovskite absorber layer that effectively extends the light path and enhances photon absorption. However, achieving such thick films requires highly concentrated precursor solutions, which typically suffer from poor crystallization control, leading to film defects and performance instability. To overcome these challenges, the researchers introduced a multifunctional additive, 1-ethyl-3-guanidinium thiourea hydrochloride (EGTHCl), to precisely regulate the nucleation and crystallization behavior of the high-concentration precursor. This approach enabled the formation of dense, uniform films with excellent crystallinity.
As a result, the optimized Bi-PSCs achieved a record-breaking power conversion efficiency (PCE) of 23.4% and reduced current loss to just 1.67 mA cm⁻². Moreover, the devices exhibited outstanding operational stability, maintaining over 80% of their initial performance (T₈₀) for more than 2000 hours under continuous illumination. This study presents a practical and scalable route for addressing photon loss in bifacial perovskite devices and paves the way toward their efficient and stable real-world application.