Interface Modification with CuCrO2 Nanocrystals for Highly Efficient and Stable Planar Perovskite Solar Cells

Critical Review of Cu-Based Hole Transport Materials for Perovskite Solar Cells: From Theoretical Insights to Experimental Validation

Despite the remarkable efficiency of perovskite solar cells (PSCs), long-term stability remains the primary barrier to their commercialization. The prospect of enhancing stability by substituting organic transport layers with suitable inorganic compounds, particularly Cu-based inorganic hole-transport materials (HTMs), holds promise due to their high valence band maximum (VBM) aligning with perovskite characteristics. This review assesses the advantages and disadvantages of these five types of Cu-based HTMs. Although Cu-based binary oxides and chalcogenides face narrow bandgap issues, the "chemical modulation of the valence band" (CMVB) strategy has successfully broadened the bandgap for Cu-based ternary oxides and chalcogenides. However, Cu-based ternary oxides encounter challenges with low mobility, and Cu-based ternary chalcogenides face mismatches in VBM alignment with perovskites. Cu-based binary halides, especially CuI, exhibit excellent properties such as wider bandgap, high mobility, and defect tolerance, but their stability remains a concern. These limitations of single anion compounds are insightfully discussed, offering solutions from the perspective of practical application. Future research can focus on Cu-based composite anion compounds, which merge the advantages of single anion compounds. Additionally, mixed-cation chalcogenides such as CuxM1-xS enable the customization of HTM properties by selecting and adjusting the proportions of cation M.

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

High-Quality TiO2 Electron Transport Film Prepared via Vacuum Ultraviolet Illumination for MAPbI3 Perovskite Solar Cells

The electron transport layer (ETL) plays an important role in determining the conversion efficiency and stability of perovskite solar cells (PSCs). Here, TiO2 thin film was prepared by irradiating diisopropoxy diacetylacetone titanium precursor thin film with 172 nm vacuum ultraviolet (VUV) at a low temperature. The prepared TiO2 thin film has higher electron mobility and conductivity. As it is used as an ETL for MAPbI3 PSCs, its band structure is better matched with the perovskite, and at the same time, due to the good interface contact, more uniform perovskite crystals are formed. Most importantly, a large number of hydroxyl radicals were formed during VUV irradiation of the precursor film, which made up for the oxygen defect present on the surface of the TiO2 thin film, and were adsorbed to the film surface. These hydroxyl groups form hydrogen bonds with methylammonium (MA) components on the MAPbI3 buried surface, thus promoting the transfer of photogenerated electrons at the MAPbI3/ETL interface. The power conversion efficiency of PSCs fabricated in air with the ETL prepared by VUV irradiation is 20.46%, which is higher than that of the contrast solar cell based on the sintered ETL (17.96%).

CuBO2 : A Potential Alternative for NiO as a Hole Acceptor Layer

P-type metal oxides, and in particular NiO, are typically used as hole accepting layers in dye-sensitized photocathodes. Delafossites (CuMO2 ) with M=B, Al, Cr or Ga have recently been proposed as attractive substitutes for NiO, with theoretically a higher hole mobility than NiO, therefore allowing a higher efficiency when the photocathode is applied in solar to fuel devices. We have experimentally validated the photoelectrochemical performance of photocathodes consisting of nanoporous CuBO2 (CBO) on Fluorine-doped Tin Oxide substrates, photosensitized with a light absorbing P1 dye. Femtosecond transient absorption and time-resolved photoluminescence studies show that light-induced hole injection occurs from the P1 dye into the CBO in a few ps, comparable to the time constant observed for NiO-based photocathodes. Importantly, the CBO-based photocathode shows significantly slower charge recombination than the NiO-based analogue. These results illustrate the promise of CBO as a p-type semiconductor in solar energy conversion devices.

Effect of novel graphitic carbon/NiO hole transporting electrode on the photovoltaic and optical performance of semi-transparent perovskite solar cells

Perovskite devices can play a critical role as tunable semi-transparent photovoltaics managing the buildings' energy health for energy harvesting, storage and utilization. Here we report ambient semi-transparent PSCs with novel graphitic carbon/NiO-based hole transporting electrodes having variable thicknesses achieving a highest efficiency of ∼14%. On the other hand, the altered thickness produced the highest average visible transparency (AVT) of the devices, nearly 35%, which also influenced other glazing-related parameters. This study envisages the impact of the electrode deposition technique on indispensable parameters like colour rendering index, correlated colour temperature, and solar factor evaluated using theoretical models to illuminate these CPSCs' colour and thermal comfort for BIPV integration. The solar factor value between 0 to 1, CRI value >80 and CCT value >4000 K make it a significant semi-transparent device. This research work suggests a possible approach to fabricating carbon-based PSC for high-performance semi-transparent solar cells.

Electron transport layer assisted by nickel chloride hexahydrate for open-circuit voltage improvement in MAPbI3 perovskite solar cells

SnO₂ is a promising electron transport layer (ETL) material with important applications in planar perovskite solar cells (PSCs). However, electron–hole recombination and charge extraction between SnO₂ and the perovskite layer necessitates further exploration. Nickel chloride hexahydrate (NiCl₂·6H₂O) was introduced into the SnO₂ ETL, which significantly increased the power conversion efficiency (PCE) from 15.49 to 17.36% and the open-circuit voltage (V_OC) from 1.078 to 1.104 V. The improved PCE and V_OC were attributed to the reduced defect states and increased energy level of the conduction band minimum. This work provides new insights into optimizing the V_OC and PCE of PSCs.

Nickel chloride hexahydrate (NiCl₂·6H₂O) was introduced into the SnO₂ ETL, which significantly increased open-circuit voltage (V_OC) and power conversion efficiency (PCE)