Bicyclopentadithiophene-Based Organic Semiconductor for Stable and High-Performance Perovskite Solar Cells Exceeding 22

Simple I-Shaped Aryl-Based Dyes for Tin Perovskite Solar Cells with Selenophene Core Moiety as Self-Assembled Monolayers on NiOx Using Two-Step Fabrication

Six novel organic small molecules, TPA-Sp-PA (1), TPA-Sp-PE (1E), TPA-T-PA (2), TPA-T-PE (2E), TPA-P-PA (3) and TPA-P-PE (3E) are developed and applied to NiOx films as self-assembled monolayers (SAMs) for tin perovskite solar cells (TPSCs). The linker between acceptor (phosphonic acid (PA) or phosphonic ester (PE)) and donor (triphenylamine (TPA)) plays an important role in facilitating the growth of high-quality perovskite films using a two-step method. Three different types of linkers, phenyl ring (P), thiophene (T), and selenophene (Sp), are studied, for which the Sp-based SAMs provide the best device performance with TPA-Sp-PE (1E) achieving a PCE 8.7%, and its acidic analog, TPA-Sp-PA (1), reaching a maximum PCE of 8.3%. Single crystal structures of TPA-Sp-PE (1E) and TPA-T-PE (2E) are successfully obtained, with the expectation that a uniform SAM would form on the NiOx/ITO substrate. The research introduces a novel approach to enhance TPSC performance by integrating organic SAMs with NiOx HTMs, offering a promising avenue for future progress in TPSC technology through a two-step fabrication technique.

Bithiophene Imide-Based Self-Assembled Monolayers (SAMs) on NiOx for High-Performance Tin Perovskite Solar Cells Fabricated Using a Two-Step Approach

Three new bithiophene imide (BTI)-based organic small molecules, BTI-MN-b4 (1), BTI-MN-b8 (2), and BTI-MN-b16 (3), with varied alkyl side chains, were developed and employed as self-assembled monolayers (SAMs) applied to NiOx films in tin perovskite solar cells (TPSCs). The NiOx layer has the effect of modifying the hydrophilicity and the surface roughness of ITO for SAM to uniformly deposit on it. The side chains of the SAM molecules play a vital role in the formation of a high-quality perovskite layer in TPSCs. The single crystal structure of BTI-MN-b8 (2) was successfully obtained, indicating that a uniform SAM can be formed on the NiOx/ITO substrate with an appropriate size of the alkyl side chain. By combining BTI-MN-b8 (2) with NiOx, a maximum PCE of 8.6% was achieved. The TPSC devices utilizing the NiOx/BTI-MN-b8 configuration demonstrated outstanding long-term stability, retaining ∼80% of their initial efficiency after 3600 h. Comprehensive characterizations, including thermal, optical, electrochemical, and morphological analyses, alongside photovoltaic evaluation, were carried out thoroughly. This study presents a pioneering strategy for improving TPSC performance, highlighting the efficacy of combining organic SAMs with NiOx as the HTM and offering a promising pathway for future advances in TPSC technology using a two-step fabrication approach.

Pyridalthiadiazole-Based Molecular Chromophores for Defect Passivation Enables High-Performance Perovskite Solar Cells

Passivation of defects at the surface and grain boundaries of perovskite films has become one of the most important strategies to suppress nonradiative recombination and improve optoelectronic performance of perovskite solar cells (PSCs). In this work, two conjugated molecules, abbreviated as CPT and SiPT, are designed and synthesized as the passivator to enhance both efficiency and stability of PSCs. The CPT and SiPT contain pyridalthiadiazole (PT) units, which can coordinate with undercoordinated Pb2+ at the surface and grain boundaries to passivate the defects in perovskite films. In addition, with the incorporation of CPT, the crystallized perovskite films exhibit more uniform grain size and smoother surface morphology relative to the control ones. The efficient passivation by CPT also results in better charge extraction and less carrier recombination in PSCs. Consequently, the CPT-passivated PSCs yield the highest power conversion efficiency (PCE) of 23.14 % together with better storage stability under ambient conditions, which is enhanced relative to the control devices with a PCE of 22.14 %. Meanwhile, the SiPT-passivated PSCs also show a slightly enhanced performance with a PCE of 22.43 %. Our findings provide a new idea for the future design of functional passivating molecules towards high-performance PSCs.

A Multifunctional Dye Molecule as the Interfacial Layer for Perovskite Solar Cells

In perovskite solar cells (PSCs), defects in the interface and mismatched energy levels can damage the device performance. Improving the interface quality is an effective way to achieve efficient and stable PSCs. In this work, a multifunctional dye molecule, named ThPCyAc, was designed and synthesized to be introduced in the perovskite/HTM interface. On one hand, various functional groups on the acceptor unit can act as Lewis base to reduce defect density and suppress nonradiative combinations. On the other hand, the stepwise energy-level alignment caused by ThPCyAc decreases the accumulation of interface carriers for facilitating charge extraction and transmission. Therefore, based on the ThPCyAc molecule, the devices exhibit elevated open-circuit voltage and fill factor, resulting in the best power conversion efficiency (PCE) of 23.16%, outperforming the control sample lacking the interface layer (PCE = 21.49%). Excitingly, when attempting to apply it as a self-assembled layer in inverted devices, ThPCyAc still exhibits attractive behavior. It is worth noting that these results indicate that dye molecules have great potential in developing multifunctional interface materials to obtain higher-performance PSCs.