The partial substitution of copper (Cu) with silver (Ag) in Cu(In,Ga)Se-2 (CIGS) thin-film solar cells represents a transformative approach to improving absorber layer properties and boosting device efficiency. This study will examine and discuss the effect of Ag alloying (0 < Ag/(Ag+Cu) < 0.3) via thermal evaporation, combined with rubidium fluoride (RbF) post-deposition treatment, on samples with bandgaps ranging from 1.1 to 1.5 eV. The approach significantly affects gallium grading, grain size, open-circuit voltage (V-oc), and fill factor (FF), achieving a power conversion efficiency (PCE) up to 20.4% for a ACIGS absorber with a 1.2 eV bandgap.

At the junction between a metal and a semiconductor there are always charge transfer phenomena that can disrupt a selective or ohmic contact. This are result of workfunction mismatches either forming a Schottky junction or by Fermi Level Pinning. This effects unless they are used for a specific purpose within the device, can be detrimental to overall efficiency of a photovoltaic solar cell. Dipole thin films are known to modify surface energy being able to completely disrupt fermi level pinning and modify Schottky junction energy barrier. In this work a summary of several dipoles sharing some similarities between them such as PFN, PEI, DNA and PAMAM have been used to prove that upscaling the strength of dipole layers provide enhanced photovoltaic results when in combination with the metallic electrode.

Synergistic interaction between 2D materials and organic molecules presents an additional dimension for tuning their intrinsic properties. Herein, we aim to tune the work function of 2D Ti3C2Tx by introducing ultrathin interlayers of organic dipoles (O.D.) with a defined dipole moment value. Interface engineering is achieved through the inclusion of poly(ethylene)amine (PEI 0.1 %) and third generation poly(amido-)amine (PAMAM G3), between the Ti3C2TX and c-Si. c-Si/O.D./Ti3C2Tx heterostructures were fabricated by simple drop casting of the aqueous MXene solution on O.D. coated c-Si substrates. Charge transport properties of the fabricated Schottky diodes with structure of c-Si/O.D./Ti3C2TX were evaluated through systematic analysis of the I-V and C-V characteristics. Our investigations reveal that diodes featuring O.D. as interlayers exhibit substantially reduced reverse saturation current density (J0) and enhanced built-in potential (Vbi). Work function of the fabricated c-Si/ MXene/O.D. structures were evaluated from the ultraviolet photo-emission spectroscopy (UPS) measurements. We report a significant reduction in the work function value of Ti3C2Tx from 5.8 eV to 4.2 eV for Ti3C2Tx/PEI 0.1 % and 3.3 eV for Ti3C2Tx/PAMAM-G3 heterostructures. Our study introduces an innovative approach for modifying the work function of Ti3C2Tx through the incorporation of O.D., highlighting the versatility of MXene electrodes to shape the future optoelectronic devices.

Low dimensional 2D materials such as graphene and carbon nano tubes have attracted significant attention from the solid-state device community and are considered as a potential candidate electrode to make functional contact with the Silicon (Si) and other industry compatible semiconductors. In this work we envisioned to utilize one such interesting 2D material Ti3C2Tx belonging to a rapidly emerging family of transition metal carbides/nitrides also known as MXene´s to fabricate the classical yet interesting Schottky junctions by simple drop casting of aqueous conducting colloidal solution of Ti3C2Tx on c-Si. Precisely, we anticipate to tune the work function of the Ti3C2Tx as well as the built-in potential of these Ti3C2Tx/c-Si Van der Waals heterojunction through inserting ultrathin interlayer of cationic polyelectrolytes/organic dipoles with a defined dipole moment value. In order to accomplish the interface engineering inclusion poly(ethylene)amine (PEI 0.1%), third generation poly(amido-)amine (PAMAM G3)), were tested between the Ti3C2TX and c-Si substrates. Charge transport properties of the fabricated Schottky devices with the structure of Ti3C2TX/organic dipole (O.D.) /c-Si were evaluated through systematic analysis of the current-voltage (I-V) and capacitance-voltage (C-V) results. I-V measurements under dark conditions revealed that Schottky diodes fabricated with the (PEI 0.1%) and PAMAM G3 interlayers exhibited lowest reverse saturation current density (J0) value and improved built in potential (Vbi) value as compared to the devices with only 2D-Ti3C2Tx as contact. We report reduction in the work function value of Ti3C2Tx from 5.8 eV to 4.2 eV for Ti3C2Tx/PEI (0.1%) and 3.3 eV for Ti3C2Tx/PAMAM G3 heterostructures. On the basis of the inferences drawn from the surface analysis we ascribe this reduction in work function value to the formation of interfacial dipoles at the Ti3C2Tx/O.D. interface. Importantly this study highlights an innovative method to tune the work function of the Ti3C2Tx MXene inclusion of organic dipoles as interlayers.

Development of carrier selective contacts for crystalline silicon solar cells has been recently of great interest toward the further expansion of silicon photovoltaics. The use of new electron and hole selective layers has opened an array of possibilities due to the low‐cost processing and non‐doping contacts. Here, a non‐doped heterojunction silicon solar cell without the use of any intrinsic amorphous silicon is fabricated using Deoxyribonucleic acid (DNA) as the electron transport layer (ETL) and transition metal oxide V 2 O 5 as the hole transport layer (HTL). The deposition and characterization of the DNA films on crystalline silicon have been studied, the films have shown a n ‐type behavior with a work function of 3.42 eV and a contact resistance of 28 mΩ cm 2 . This non‐doped architecture has demonstrated a power conversion efficiency of 15.6%, which supposes an increase of more than 9% with respect to the cell not containing the biomolecule, thus paving the way for a future role of nucleic acids as ETLs.

Poly(amidoamine) (PAMAM) dendrimers are used to modify the interface of metal-semiconductor junctions. The large number of protonated amines contributes to the formation of a dipole layer, which finally serves to form electron-selective contacts in silicon heterojunction solar cells. By modification of the work function of the contacts, the addition of the PAMAM dendrimer interlayer quenches Fermi level pinning, thus creating an ohmic contact between the metal and the semiconductor. This is supported by the observation of a low contact resistivity of 4.5 mΩ cm2, the shift in work function, and the n-type behavior of PAMAM dendrimer films on the surface of crystalline silicon. A silicon heterojunction solar cell containing the PAMAM dendrimer interlayer is presented, which achieved a power conversion efficiency of 14.5%, an increase of 8.3% over the reference device without the dipole interlayer.

High open-circuit voltage in Sb2Se3 thin-film solar cells is a key challenge in the development of earth-abundant photovoltaic devices. CdS selective layers have been used as the standard electron contact in this technology. Long-term scalability issues due to cadmium toxicity and environmental impact are of great concern. In this study, we propose a ZnO-based buffer layer with a polymer-film-modified top interface to replace CdS in Sb2Se3 photovoltaic devices. The branched polyethylenimine layer at the ZnO and transparent electrode interface enhanced the performance of Sb2Se3 solar cells. An important increase in open-circuit voltage from 243 mV to 344 mV and a maximum efficiency of 2.4% was achieved. This study attempts to establish a relation between the use of conjugated polyelectrolyte thin films in chalcogenide photovoltaics and the resulting device improvements.

This work studies the use of thin layers of polyethylenimine (PEI) as an interface film to produce electron selective contacts for photovoltaic applications in crystalline silicon. Generally, in conjugated polyelectrolytes such as PEI with a high Lewis basicity, charge is accumulated along the chain of the polymer and counter anions from the solvent create an intense dipole array. In this work, part of the amine groups in PEI are protonated by the solvent that behaves as a weak Brønsted acid during the process. The PEI band modification is able to eliminate Fermi level pinning at metal/semiconductor junctions as it shifts the work function of the metallic electrode by more than 1 eV. As a consequence, induced charge transport between the metal and the semiconductor forms an electron accumulation region and promotes enhanced selectivity.

This work studies the use of polymeric layers of polyethylenimine (PEI) as an interface modification of electron-selective contacts. A clearly enhanced electrical transport with lower contact resistance and significant surface passivation (about 3 ms) can be achieved with PEI modification. As for other conjugated polyelectrolytes, protonated groups of the polymer with their respective counter anions from the solvent create an intense dipole. In this work, part of the amine groups in PEI are protonated by ethanol that behaves as a weak Bronsted acid during the process. A comprehensive characterization including high-resolution compositional analysis confirms the formation of a dipolar interlayer. The PEI modification is able to eliminate completely Fermi-level pinning at metal/ semiconductor junctions and shifts the work function of the metallic electrode by more than 1 eV. Induced charge transport between the metal and the semiconductor allows the formation of an electron accumulation region. Consequently, electron-selective contacts are clearly improved with a significant reduction of the specific contact resistance (less than 100 m omega.cm(2)). Proof-of-concept dopant-free solar cells on silicon were fabricated to demonstrate the beneficial effect of PEI dipolar interlayers. Full dopant-free solar cells with conversion efficiencies of about 14% could be fabricated on flat wafers. The PEI modification also improved the performance of classical high-efficiency heterojunction solar cells.

Sputtered films of reduced molybdenum oxide (MoOx) with a molybdenum trioxide target in different pressures and atmospheres were deposited in varying temperatures. Compositional, optic, and electric characteristics of the samples were studied. X-ray photoelectron spectroscopy revealed reduced states when working in the hydrogen + argon atmosphere implying that stoichiometry could be controlled by adding some hydrogen in the sputtering chamber. The effect of slightly increasing the substrate temperature during deposition was also studied and lead to the presence of metastable Mo4+ states at 3 mTorr. Optical properties match the ones already in the literature, and transmittances of 90% were achieved. The results support sputtering as a viable method of depositing MoOx films apart from thermal evaporation for many applications.

As optoelectronic devices continue to improve, control over film thickness has become crucial, especially in applications that require ultra-thin films. A variety of undesired effects may arise depending on the specific growth mechanism of each material, for instance a percolation threshold thickness is present in Volmer-Webber growth of materials such as silver. In this paper, we explore the introduction of aluminum in silver films as a mechanism to grow ultrathin metallic films of high transparency and low sheet resistance, suitable for many optoelectronic applications. Furthermore, we implemented such ultra-thin metallic films in Dielectric/Metal/Dielectric (DMD) structures based on Aluminum-doped Zinc Oxide (AZO) as the dielectric with an ultra-thin silver aluminum (Ag:Al) metallic interlayer. The multilayer structures were deposited by magnetron sputtering, which offers an industrial advantage and superior reliability over thermally evaporated DMDs. Finally, we tested the optimized DMD structures as a front contact for n-type silicon solar cells by introducing a hole-selective vanadium pentoxide (V2O5) dielectric layer.

Dielectric/metal/dielectric structures based on vanadium pentoxide with a thin silver interlayer have been optimized to replace traditional transparent electrodes. As would be expected, there is a tradeoff in the metal thickness to achieve high transparency and low sheet resistance simultaneously. It has been demonstrated that an ultra-thin gold seed prevents the tendency of silver to form clusters. This wetting effect reduces the metal thickness needed to form a continuous film, which leads to a higher averaged transmittance and very low sheet resistance. On the other hand, vanadium pentoxide on silicon forms a high-quality hole-selective contact. Thus, these structures can be used as an all-in-one transparent electrode and selective contact for a new kind of heterojunction solar cells. This concept has been proved in a 13.3% efficient solar cell fabricated on n-type silicon wafers. Besides being dopant-free, the complete fabrication route did not require any sputtered transparent electrode.