Explore the vast range of titles available.

By combining the most successful heterojunctions (HJ) with interdigitated back contacts, crystalline silicon (c‐Si) solar cells (SCs) have recently demonstrated a record efficiency of 26.6%. However, such SCs still introduce optical/electrical losses and technological issues due to parasitic absorption/Auger recombination inherent to the doped films and the complex process of integrating discrete p+‐ and n+‐HJ contacts. These issues have motivated the search for alternative new functional materials and simplified deposition technologies, whereby carrier‐selective contacts (CSCs) can be formed directly with c‐Si substrates, and thereafter form IBC cells, via a dopant‐free method. Screening and modifying CSC materials in a wider context is beneficial for building dopant‐free HJ contacts with better performance, shedding new light on the relatively mature Si photovoltaic field. In this review, a significant number of achievements in two representative dopant‐free hole‐selective CSCs, i.e., poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate)/Si and transition metal oxides/Si, have been systemically presented and surveyed. The focus herein is on the latest advances in hole‐selective materials modification, interfacial passivation, contact resistivity, light‐trapping structure and device architecture design, etc. By analyzing the structure–property relationships of hole‐selective materials and assessing their electrical transport properties, promising functional materials as well as important design concepts for such CSCs toward high‐performance SCs have been highlighted. Carrier‐selective dopant‐free contacts with Si are of great interest to both fundamental researchers and the photovoltaic industry due to the extreme simplifications in device structure and manufacturing procedure. Here, recent advances and open challenges in two typical hole‐selective designs of organic poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and transition metal oxides are reported, examining the topic from both the materials and device engineering.

The evolution of the contact scheme has driven the technology revolution of crystalline silicon (c‐Si) solar cells. The state‐of‐the‐art high‐efficiency c‐Si solar cells such as silicon heterojunction (SHJ) and tunnel oxide passivated contact (TOPCon) solar cells are featured with passivating contacts based on doped Si thin films, which induce parasitic optical absorption loss and require capital‐intensive deposition processes involving flammable and toxic gasses. A promising solution to tackle this problem is to employ dopant‐free passivating contact, involving the use of transparent and cost‐effective wide band gap materials. In this review, we first introduce the dopant‐free passivating contact, from carrier transport mechanisms, material classification to evaluation methods. Then we focus on the advances in different strategies to improve cell performance, including material property optimization, structural and interfacial engineering, as well as various post‐treatments. At the end, the challenge and perspective of dopant‐free passivating contact c‐Si solar cells are discussed. This article provides an overview of the mechanism and materials of dopant‐free passivating contacts for crystalline silicon solar cells, and focuses on the recent advances in contact configuration and interface engineering for efficiency and stability enhancement.

Achieving efficient passivating carrier‐selective contacts (PCSCs) plays a critical role in high‐performance photovoltaic devices. However, it is still challenging to achieve both an efficient carrier selectivity and high‐level passivation in a sole interlayer due to the thickness dependence of contact resistivity and passivation quality. Herein, a light‐promoted adsorption method is demonstrated to establish high‐density Lewis base polyethylenimine (PEI) monolayers as promising PCSCs. The promoted adsorption is attributed to the enhanced electrostatic interaction between PEI and semiconductor induced by the photo‐generated carriers. The derived angstrom‐scale PEI monolayer is demonstrated to simultaneously provide a low‐resistance electrical contact for electrons, a high‐level field‐effect passivation to semiconductor surface and an enhanced interfacial dipole formation at contact interface. By implementing this light‐promoted adsorbed PEI as a single‐layered PCSC for n‐type silicon solar cell, an efficiency of 19.5% with an open‐circuit voltage of 0.641 V and a high fill factor of 80.7% is achieved, which is one of the best results for devices with solution‐processed electron‐selective contacts. This work not only demonstrates a generic method to develop efficient PCSCs for solar cells but also provides a convenient strategy for the deposition of highly uniform, dense, and ultra‐thin coatings for diverse applications. A light‐promoted adsorption method is introduced to establish high‐density Lewis‐base polyethylenimine monolayers, which simultaneously provide a low‐resistance contact for electrons, a high‐quality field‐effect passivation to semiconductor and an enhanced dipole formation at semiconductor/cathode interface, as promising passivating carrier‐selective contacts for solar cells. This work also provides a convenient strategy to deposit highly uniform, dense, and ultra‐thin coatings for diverse applications.

Monolithic perovskite–silicon tandem solar cells with MoOx hole selective contact silicon bottom solar cells show a power conversion efficiency of 8%. A thin 15 nm-thick MoOx contact to n-type Si was used instead of a standard p+ emitter to collect holes and the SiOx/n+ poly-Si structure was deposited on the other side of the device for direct tunneling of electrons and this silicon bottom cell structure shows ~15% of power conversion efficiency. With this bottom carrier selective silicon cell, tin oxide, and subsequent perovskite structure were deposited to fabricate monolithic tandem solar cells. Monolithic tandem structure without ITO interlayer was also compared to confirm the role of MoOx in tandem cells and this tandem structure shows the power conversion efficiency of 3.3%. This research has confirmed that the MoOx layer simultaneously acts as a passivation layer and a hole collecting layer in this tandem structure.

Contact selectivity is a key parameter for enhancing and improving the power conversion efficiency (PCE) of crystalline silicon (c-Si)-based solar cells. Carrier selective contacts (CSC) are the key technology which has the potential to achieve a higher PCE for c-Si-based solar cells closer to their theoretical efficiency limit. A recent and state-of-the-art approach in this domain is the tunnel oxide passivated contact (TOPCon) approach, which is completely different from the existing classical heterojunction solar cells. The main and core element of this contact is the tunnel oxide, and its main role is to cut back the minority carrier recombination at the interface. A state-of-the-art n-type c-Si-based TOPCon solar cell featuring a passivated rear contact was experimentally analyzed, and the highest PCE record of ~25.7% was achieved. It has a high fill factor (FF) of ~83.3%. These reported results prove that the highest efficiency potential is that of the passivated full area rear contact structures and it is more efficient than that of the partial rear contact (PRC) structures. In this paper, a review is presented which considers the key characteristics of TOPCon solar cells, i.e., minority carrier recombination, contact resistance, and surface passivation. Additionally, practical challenges and key issues related to TOPCon solar cells are also highlighted. Finally, the focus turns to the characteristics of TOPCon solar cells, which offer an improved and better understanding of doping layers and tunnel oxide along with their mutual and combined effect on the overall performance of TOPCon solar cells.

Recently, titanium oxide has been widely investigated as a carrier-selective contact material for silicon solar cells. Herein, titanium oxide films were fabricated via simple deposition methods involving thermal evaporation and oxidation. This study focuses on characterizing an electron-selective passivated contact layer with this oxidized method. Subsequently, the SiO2/TiO2 stack was examined using high-resolution transmission electron microscopy. The phase and chemical composition of the titanium oxide films were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The passivation quality of each layer was confirmed by measuring the carrier lifetime using quasi-steady-state photoconductance, providing an implied open circuit voltage of 644 mV. UV–vis spectroscopy and UV photoelectron spectroscopy analyses demonstrated the band alignment and carrier selectivity of the TiO2 layers. Band offsets of ~0.33 and ~2.6 eV relative to the conduction and valence bands, respectively, were confirmed for titanium oxide and the silicon interface.

We report an organic luminescent small molecule, Bis(1-phenylisoquinoline) (acetylacetonate) iridium(III) or Ir(piq)2(acac), that can function as a stable and efficient hole selective contact (HSC) for crystalline silicon (c-Si) solar cells. The devices with the Ir(piq)2(acac) HSC exhibit superior charge transport properties and high stability for up to 30 days in the air without packaging. The photovoltaic characteristics with the solution-processed Ir(piq)2(acac) HSC exhibit little dependence on the blade coating speed and film thickness, demonstrating tolerance to coating and thickness variations. Moreover, the series resistance of the solar cells and the surface work function of the Ir(piq)2(acac) HSCs exhibit analogous correlations to the annealing temperature, suggesting that the fill factor (FF) enhancement originates from an upward energy band bending and a reduced barrier height which facilitates hole transport and collection. The conventional c-Si solar cell incorporating an Ir(piq)2(acac) HSC achieves a 17.8% power conversion efficiency (PCE) with a 78.9% FF, both exceeding the reference counterpart with a 16.9% PCE and 76.8% FF. This work opens up possibilities for exploring a variety of organic luminescent small molecules as efficient hole selective contacts in high-efficiency and low-cost silicon photovoltaics.Graphic Abstract

The development of efficient contact schemes curtailing losses due to recombination at directly metalized contacts is the final remaining bottleneck towards approaching the theoretical efficiency limit of silicon solar cells. Given their market domination, the silicon cells demand contact structures that provide passivation of defects at the interface while simultaneously allowing selective extraction of only one type of carrier. Carrier selective contacts are the pivotal research interests to bring about the further advancement of semiconductor solar cells. This review attempts to summarize the elusive classification, fundamental theory and research efforts of carrier selective passivating contact schemes compatible with silicon solar cells. The need for passivation and contact selectivity is identified and the work up to date is comprehensively reviewed. Further, the electrical and optical comparison metrics for these contact schemes are discussed briefly and the challenges to their mainstream PV incorporation are highlighted.

Performance of silicon solar cells using pure and Cd-doped SnSe as back surface field (BSF) layers in p-type Si wafer and n + -Si emitter has been simulated. Replacing n + -Si emitter with metal oxides, namely Cadmium oxide (CdO) and Tin oxide (SnO 2 ), the improvement could be achieved in the solar cell parameters open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) and efficiency (η). Moreover, deposition of these oxides can be done at much lower temperatures compared to diffused Si emitters diffused at high temperatures. Also, the doped Si emitters make use of poisonous gases like diborane and phosphine. In this work, a low thermal budget silicon solar cell with pure and Cd-doped SnSe BSF and metal oxide emitters has been prepared.

In this research, simulations were performed to investigate the effects of carrier selective front contact (CSFC) layer and defect state of hydrogenated amorphous silicon passivation layer/n-type crystalline silicon interface in silicon heterojunction (SHJ) solar cells employing the Automat for Simulation of hetero-structure (AFORS-HET) simulation program. The results demonstrated the effects of band offset determined by band bending at the interface of the CSFC layer/passivation layer. In addition, the nc-SiOx: H CSFC layer not only reduces parasitic absorption loss but also has a tunneling effect and field effect passivation. Furthermore, it increased the selectivity of contact. In the experimental cell, nc-SiOx:H was used as the CSFC layer, where efficiency of the SHJ solar cell was 22.77%. Our investigation shows that if a SiOx layer passivation layer is used, the device can achieve efficiency up to 25.26%. This improvement in the cell is mainly due to the enhancement in open circuit voltage (Voc) because of lower interface defect density resulting from the SiOx passivation layer.