Double-side 2D/3D heterojunctions for inverted perovskite solar cells.

Defects at the top and bottom interfaces of three-dimensional (3D) perovskite photoabsorbers diminish the performance and operational stability of perovskite solar cells owing to charge recombination, ion migration and electric-field inhomogeneities1-5. Here we demonstrate that long alkyl amine ligands can generate near-phase-pure 2D perovskites at the top and bottom 3D perovskite interfaces and effectively resolve these issues. At the rear-contact side, we find that the alkyl amine ligand strengthens the interactions with the substrate through acid-base reactions with the phosphonic acid group from the organic hole-transporting self-assembled monolayer molecule, thus regulating the 2D perovskite formation. With this, inverted perovskite solar cells with double-side 2D/3D heterojunctions achieved a power conversion efficiency of 25.6% (certified 25.0%), retaining 95% of their initial power conversion efficiency after 1,000 h of 1-sun illumination at 85 °C in air.

Environment-friendly copper-based chalcogenide thin film solar cells: status and perspectives.

Copper chalcogenides (CuCh) have attracted considerable attention due to their promising potential as environmental-friendly photoactive material for lightweight and flexible thin film solar cells. Further, CuCh can be fabricated from simple to complex chemical compositions and offer a remarkable charge carrier mobility and excellent absorption coefficient with a desirable bandgap (up to ∼1.0 eV). Currently, they have demonstrated maximum power conversion efficiencies of over 23% for single-junction, around 25% and 28% for monolithic 2-Terminal (2T) and mechanically-stacked 4-Terminal (4T) perovskite/CuCh tandem solar cells, respectively. This article presents an overview of CuCh-based materials, from binary- to quaternary-CuCh compounds for single- and multi-junction solar cells. Then, we discuss the development of fabrication methods and the approaches taken to improve the performance of CuCh-based thin film itself, including chemical doping, the development of complement layers, and their potential application in flexible and lightweight devices. Finally, these technologies' stability, scalability, and toxicity aspects are discussed to enhance their current marketability.

Mitigating the Undesirable Chemical Reaction between Organic Molecules for Highly Efficient Flexible Organic Photovoltaics.

Organic photovoltaics (OPVs) with nonfullerene acceptors (NFAs) feature excellent device performance and device stability. However, they are facing problems when the amine-rich polyelectrolytes are used as cathode interfacial layers. In this work, a small molecule, ethanedithiol (EDT) at the polyethyleneimine ethoxylated (PEIE)/active layer interface is inserted for mitigating the undesirable reaction between amine-rich groups and electron-acceptor moieties in NFA. The main role of EDT is to passivate the PEIE surface and prevent electron flow to NFA and the unwanted reaction can be mitigated. It improves the performance of OPV devices by reducing the work function, decreasing trap-assisted recombination, and improving electron-mobility. As a result, the flexible device with the PEIE interfacial layer with a power conversion efficiency (PCE) of 7.20% can be improved to 10.11% after the inclusion of EDT. Moreover, EDT-modified device can retain 98.18% after it is bent for 200 cycles and can maintain 80.83% of its initial PCE under continuous light illuminated in ambient conditions without any encapsulation. Based on these findings, the proposed strategy constitutes a crucial step toward highly efficient flexible OPVs.

The role of cation and anion dopant incorporated into a ZnO electron transporting layer for polymer bulk heterojunction solar cells.

Doping is a widely-implemented strategy for enhancing the inherent electronic properties of charge transport layers in photovoltaic devices. A facile solution-processed zinc oxide (ZnO) and various cation and anion-doped ZnO layers were synthesized via the sol-gel method and employed as electron transport layers (ETLs) for inverted polymer solar cells (PSCs). The results indicated that all PSCs with doped ZnO ETLs exhibited better photovoltaic performance compared with the PSCs with a pristine ZnO ETL. By exploring the role of various anion and cation dopants (three compounds with the same Al3+ cation: Al(acac)3, Al(NO3)3, AlCl3 and three compounds with the same Cl- anion: NH4Cl, MgCl2, AlCl3), we found that the work function changed to favor electronic extraction only when the Cl anion was involved. In addition, the conductivity of ZnO was enhanced more with the Al3+ cation. Therefore, in inverted solar cells, doping with Al3+ and Cl- delivered the best power conversion efficiency (PCE). The maximum PCE of 10.38% was achieved from the device with ZnO doped with Al+ and Cl-.