Lead halide perovskites suffer from toxicity and instability challenges due to their sensitivity to various environmental factors, such as humidity, heat and prolonged light illumination. Developing stable and lead-free alternatives that can still be solution-processed has attracted significant research interests in the past years. Bismuth-based chalcogenide materials have emerged as one promising candidate. In particular, silver bismuth disulfide (AgBiS2) has garnered increasing interest due to its high absorption coefficient (10⁵-10³ cm⁻¹ in the 400-1100 nm range) and a favourable bandgap of ~1.3 eV. However, the poor solubility of AgBiS₂ precursors in the conventional solvents has hindered the solution fabrication of high-quality thin-films. While previous studies have explored deposition techniques such as spray pyrolysis, hot-injection synthesis with ligand exchange, and nanocrystal ink-based in situ passivation, these methods often involve complex ligand engineering, high processing costs, or challenges in achieving uniform and compact thin-film. In this work, we introduce a novel solution-based spin-coating approach for the deposition of high-quality, phase-pure AgBiS₂ thin-films, overcoming the solubility limitations of conventional precursors. By employing a binary chelating solvent mixture of ethylenediamine and 1,2-ethanedithiol, we achieve bidentate coordination with metal cations, enabling the dissolution of Ag₂S and Bi₂S₃ through a chelation-assisted mechanism. This facilitates the formation of compact and uniform films with precise roughness control. This method eliminates the need for high-temperature processing or vacuum-assisted crystallization, significantly enhancing scalability and cost-effectiveness. A planar heterojunction device architecture incorporating TiO₂ as the electron transport layer (FTO/c-TiO₂/AgBiS₂/P₃HT/Au) is demonstrated with the initial power conversion efficiency (PCE) of 0.62%, offering an effective charge extraction pathway. With further passivation and doping optimizations, this approach presents a new, scalable route for solution-processed AgBiS₂ thin-films, providing a promising alternative to ligand-engineered nanocrystal-based methods with potential advantages in stability, reproducibility, and manufacturing compatibility.

Despite the successful application of self-assembled molecules (SAMs) as hole-selective contacts in light-emitting diodes (LEDs), examples of the use of electron-selective SAMs are scarce. Here, we investigate the potential of naphthalene diimide (NDI) as an efficient electron-selective contact in CdSe@ZnS-based LEDs. CdSe@ZnS quantum dots, due to their exceptional optical properties, have found a range of applications in optoelectronics. In particular, they have been widely studied in LEDs because of their stability, tunable and narrow emission, and high photoluminescence quantum yields. In this work, two SAMs based on NDI cores have been synthesized, incorporating different terminal groups to study their structure-device function relationship. SAM3 contains one carboxylic acid moiety and one long alkyl chain as its substituents, whereas in SAM12, both substituents are carboxylic acids. Both inverted (n-i-p) and regular (p-i-n) device configurations have been explored and analyzed and our results show that the substituents play an important role in controlling device characteristics. Therefore, the application of NDI derivatives as electron selective contacts have been demonstrated opening the door for further research into the underexplored field of electron selective SAMs in optoelectronic devices.

Bifacial perovskite solar cells (PSCs) offer the potential for higher power output through tandem configurations with silicon solar cells or by harvesting light from both sides. A high-transmittance and low-resistance transparent electrode is crucial for bifacial PSCs. However, the most widely used transparent conductive oxide (TCO) as transparent electrodes often require energetic ion bombardment during deposition and high post-annealing temperatures to obtain high transmittance and low resistance, making them incompatible for direct deposition onto delicate perovskite films. In this work, a cerium-doped indium oxide (ICO) film, prepared via radio frequency (RF) magnetron sputtering at room temperature (RT), is employed as the top transparent conductive electrode in bifacial PSCs. A 20 nm MoOx layer is introduced as a buffer layer to protect the underlying spiro-OMeTAD and perovskite layers against sputtering damage. The ICO film, deposited with an RF power of 80 W for 1 h and 20 min at RT, exhibits an amorphous structure with a thickness of 210 nm, a mobility of 8.3 cm²/Vs, a carrier concentration of 6.07 × 10²⁰ cm⁻³, a resistivity of 1.24 × 10⁻³ Ω·cm, and an average transmittance of 89.70% between 550 nm and 1000 nm, resulting in a figure of merit (FOM) of 6.67 × 10⁻³ Ω⁻¹. The fabricated bifacial PSC demonstrates power conversion efficiencies (PCEs) of 15.28% and 10.00% when illuminated from the FTO side and ICO side, respectively. Furthermore, the bifacial PSC under simultaneous illumination from both sides achieves a superior power density compared to the monofacial PSC in albedo utilization. Finally, by mechanically stacking the bifacial PSC as the top cell with a passivated emitter rear contact (PERC) crystalline silicon solar cell as the bottom cell, the 4-terminal perovskite/silicon tandem solar cell achieves a PCE of 21.89%.