Inorganic Hole Transport Materials Research Articles

Air-Stable n–i–p Planar Perovskite Solar Cells Using Nickel Oxide Nanocrystals as Sole Hole-Transporting Material

Development of low-cost solution processable inorganic hole-transporting materials (HTM) in n–i–p perovskite solar cells (PSCs) is still a challenge toward stable and cost-effective devices. Here, ...

Enhanced Efficiency of Carbon-Based Mesoscopic Perovskite Solar Cells through a Tungsten Oxide Nanoparticle Additive in the Carbon Electrode

This paper presents perovskite solar cells employed with WO3 nanoparticles embedded carbon top electrode. WO3 nanoparticles works as an inorganic hole-transport material (HTM) to promote the hole-extraction in the perovskite/carbon interface as revealed by efficiency, electrochemical impedance and external quantum efficiency measurements. As a result, a 40% enhancement of energy conversion efficiency has been achieved compared to the reference devices with the energy conversion efficiency of 10.77% under standard conditions. In addition, the Li-TFSI can modify the interface between electron-transport material (ETM) and perovskite, which may inhibit the recombination at the ETM/perovskite interface. The VOC of devices upon the modification of Li-TFSI is increased from 887.9 to 934.2 mV. This work highlights about the enlightenment of the effective performance of carbon-based mesoscopic PSCs by the introduction of HTM and the modification of interfaces.

Thermally stable methylammonium-free inverted perovskite solar cells with Zn2+ doped CuGaO2 as efficient mesoporous hole-transporting layer

Despite incredible success has been achieved for perovskite solar cells (PSCs) in pursuing high power conversion efficiency (PCE), their practical application is prevented by the low stability issues, especially an accelerating stability test at high temperature still needs to be demonstrated. Herein, we present an inverted mesoscopic PSCs with Zn2+ doped CuGaO2 (Zn:CuGaO2) as both the scaffold and hole transporting materials (HTM). Both theoretical and experimental results indicate that the carrier density and conductivity of CuGaO2 is significantly improved via Zn2+ doping, which is beneficial for the hole transfer. Moreover, the mesoporous structure combined with the well matched energy levels between Zn:CuGaO2 and perovskite can effectively extract holes from perovskite, reduce charge transfer barrier, and depress the charge-carrier recombination. As a result, the champion device with Zn:CuGaO2 as HTM gives a power conversion efficiency of 20.67% from reverse scan and a stabilized efficiency of 20.15%, which is among the best results for PSCs based on methylammonium-free, cesium-formamidinium (Cs-FA) double-cation perovskite and inorganic HTM. Moreover, PCE of the unencapsulated device retains over 85% after thermal annealing at 85 °C for 1000 h in a nitrogen atmosphere, demonstrating the superior thermal stability of the present PSCs with the metal doped inorganic HTM.

Theoretical Device Engineering for High‐Performance Perovskite Solar Cells Using CuSCN as Hole Transport Material Boost the Efficiency Above 25%

Recently, perovskite solar cells (PSCs) have achieved remarkable power conversion efficiency (PCE) about 22.6%. While most of the hole transport materials (HTMs) used in PSCs are organic in nature with an issue of instability and high cost. In this paper, copper thiocyanate (CuSCN), a low cost inorganic HTM with excellent thermal and moisture stability, is applied as HTM for perovskite solar cells. The device modeling of PSCs is based on the device structure of FTO/TiO2/MAPbI3/CuSCN/Au. Two interface defect layers, IDL1 as electron transport material (ETM)/absorber interface and IDL2 as absorber/HTM interface, are introduced into the device model in order to study the impact of interface quality on the performance of PSCs. Among all of the parameters, defect density and conduction band offset (CBO) at ETM/absorber interface together with the defect density of absorber influence the device performance appreciably. Upon optimization of all of the parameters, PCE of the device approaches to 25.02%, which is very encouraging. The result shows that lead‐based PSC with CuSCN as HTM is an efficient system due to its enhanced hole transport, high electric conductivity, and improved chemical interaction with absorber. Further, defect density of ETM/absorber interface and absorber layer could be reduced by optimized deposition process.

The effect of HTM on the performance of solid-state dye-sanitized solar cells (SDSSCs): a SCAPS-1D simulation study

In this paper, we have investigated the performance of solid-state dye-sensitized solar cells (SDSSCs) fabricated from four different hole transport materials (HTMs) through SCAPS-1D simulation. Two organic and two inorganic HTM layers are examined in this study. The structure of SDSSC employed in this work is composed of FTO/TiO2/N719/HTM/Au and only the HTM layer is changed for each simulation. The materials employed as HTM are PEDOT:PSS, Spiro-OMETAD, CuI, and CuSCN. In each case, the VOC, JSC, FF, PCE, and quantum efficiency parameters are analyzed. The effects of HTM type and thickness, temperature and hole concentration on different parameters of the SDSSCs are compared with each other. The results indicate that using CuI as HTM yields better performance in comparison with other HTMs and can reach an efficiency of 17.72%. The simulation results can be used to make a comparison between organic and inorganic HTMs and also to improve the parameters of conductive polymers with secondary doping and to fabricate optimized SDSSCs in laboratory and industrial scales.

Nickel Oxide as Efficient Hole Transport Materials for Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) have achieved great success in recent years with a demonstrated power conversion efficiency (PCE) increasing rapidly from 3.8% to 22.3% for single junction devices. Most high‐performance PSCs consist of a perovskite absorber sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL), which extracts electrons (holes) and blocks holes (electrons) from the absorber efficiently. Inorganic hole transport materials have extracted extensive attention due to their higher mobility and better stability. Particularly, the excellent hole selective transport property of nickel oxide (NiOx) has been highlighted by its recent application in organometallic halide PSCs, due to the favorable band alignment formed between the halide perovskite absorber and NiOx HTL. This comprehensive review summarizes the recent progress in the fabrication of NiOx films and their application in PSCs. Special attention is paid to the optoelectronic properties of NiOx films, which strongly depend on the synthesis methods and post‐treatment conditions, as well as the resulting photovoltaic device performance. Surface modification and doping strategies that are used to improve the optoelectronic properties of NiOx films and the resulting device performance are discussed with emphasis. Finally, a short perspective of NiOx‐based PSCs is also provided.

Toward development of high-performance perovskite solar cells based on CH3NH3GeI3 using computational approach

We reported numerical simulations of device performances made of methylammonium germanium halide (CH3NH3GeI3)-based perovskite solar cells. The main goal here is to seek for an efficient method to improve the device efficiency of alternative lead-free perovskite based on germanium solar cells by using various organic and inorganic hole transport materials. For that aspiration, the effect of several parameters on the solar cell performance were investigated such as thicknesses of perovskite, HTM, defect density, hole mobility, and metal electrode work function on the charge collection. The device simulation revealed that the optimum thickness of CH3NH3GeI3 absorber is found around 600 nm. Furthermore, Ge-based perovskite solar cells with Cu2O and D-PBTTT-14 as HTM exhibited a remarkable overall power conversion efficiency reaching 21%. The defect density reduction is a critical factor to improve the solar cell performance and should be controlled under the order of ∼1015 cm3. Further simulations were performed to study the effect of operating temperature on the performance. Our simulation results advocate for a viable route to design hole-transporting materials for highly efficient and stable perovskite solar cells with low cost.

Cu2ZnSnS4 Quantum Dots as Hole Transport Material for Enhanced Charge Extraction and Stability in All‐Inorganic CsPbBr3 Perovskite Solar Cells

All‐inorganic CsPbBr3 perovskite solar cells (PSCs) have recently generated tremendous interest in next‐generation cost‐effective and stable photovoltaic devices. However, the commonly used costly and unstable organic hole transporting material (HTM) has so far prevented the further development and large‐scale application of PSCs. In this work, Cu2ZnSnS4 quantum dots (CZTS QDs) are exploited as a novel inorganic HTM for CsPbBr3 PSCs. Due to the well‐matched energy levels with the inorganic perovskite layer, a decent power conversion efficiency of 4.84% is achieved, which is quite comparable to the efficiency of the traditional device based on spiro‐OMeTAD HTM (5.36%). Moreover, the photoluminescence (PL) and impedance spectroscopy further demonstrate the more effective hole extraction and transfer properties of the CZTS QDs interface layer, making it a promising material for fabricating efficient and stable PSCs toward practical applications.

Tuning the Excited-State Dynamics of CuI Films with Electrochemical Bias.

Owing to its high hole conductivity and ease of preparation, CuI was among the first inorganic hole-transporting materials that were introduced early on in metal halide perovskite solar cells, but its full potential as a semiconductor material is still to be realized. We have now performed ultrafast spectroelectrochemical experiments on ITO/CuI electrodes to show the effect of applied bias on the excited-state dynamics in CuI. Under operating conditions, the recombination of excitons is dependent on the applied bias, and it can be accelerated by decreasing the potential from +0.6 to −0.1 V vs Ag/AgCl. Prebiasing experiments show the persistent and reversible “memory” effect of electrochemical bias on charge carrier lifetimes. The excitation of CuI in a CuI/CsPbBr3 film provides synergy between both CuI and CsPbBr3 in dictating the charge separation and recombination.

Copper sulfide nanoparticles as hole-transporting-material in a fully-inorganic blocking layers n-i-p perovskite solar cells: Application and working insights

One of the challenges in the field of perovskite solar cells (PSC) is the development of inorganic hole-transporting-materials (HTM) suitable for solution-processed deposition, in order to have cheaper, more stable and scalable devices. Herein, we report the synthesis and characterization of p-type copper sulfide nanoparticles for their application for the first time as a low-cost, fully-inorganic HTM in mesoscopic n-i-p PSC. By employing CuS combined with two different perovskites, CH3NH3PbI3 (MAPbI3) and (FAPbI3)0.78(MAPbBr3)0.14(CsPbI3)0.08 (CsFAMAPbIBr), very high current densities and fill-factors are observed, suggesting an effective hole-extraction happening at the CuS interface. Noticeable, our cells exhibit one of the highest power conversion efficiencies (PCE) in n-i-p configuration employing a sole solution-processed inorganic HTM via non-toxic solvents, leading to 13.47% and 11.85% for MAPbI3 and CsFAMAPbIBr, respectively. As a remark, such PCE values are only limited by a reduced open-circuit voltage around 0.8 V, due to different phenomena occurring at perovkite/CuS interface such as an increased non-radiative recombination, caused by considerable difference in valence band value, and the effect of CuS metallic character. Overall, these findings highlight CuS as an extremely cheap alternative to common organic HTMs and pave the way to new improvements employing this material in full-inorganic blocking layers PSC.

Bifacial Passivation of Organic Hole Transport Interlayer for NiO x -Based p-i-n Perovskite Solar Cells.

Methoxy‐functionalized triphenylamine‐imidazole derivatives that can simultaneously work as hole transport materials (HTMs) and interface‐modifiers are designed for high‐performance and stable perovskite solar cells (PSCs). Satisfying the fundamental electrical and optical properties as HTMs of p‐i‐n planar PSCs, their energy levels can be further tuned by the number of methoxy units for better alignment with those of perovskite, leading to efficient hole extraction. Moreover, when they are introduced between perovskite photoabsorber and low‐temperature solution‐processed NiOx interlayer, widely featured as an inorganic HTM but known to be vulnerable to interfacial defect generation and poor contact formation with perovskite, nitrogen and oxygen atoms in those organic molecules are found to work as Lewis bases that can passivate undercoordinated ion‐induced defects in the perovskite and NiOx layers inducing carrier recombination, and the improved interfaces are also beneficial to enhance the crystallinity of perovskite. The formation of Lewis adducts is directly observed by IR, Raman, and X‐ray photoelectron spectroscopy, and improved charge extraction and reduced recombination kinetics are confirmed by time‐resolved photoluminescence and transient photovoltage experiments. Moreover, UV‐blocking ability of the organic HTMs, the ameliorated interfacial property, and the improved crystallinity of perovskite significantly enhance the stability of PSCs under constant UV illumination in air without encapsulation.

An inorganic hole-transport material of CuInSe2 for stable and efficient perovskite solar cells

Abstract In this work, we synthesized CuInSe2 quantum dots (CISe QDs) and applied them to perovskite solar cells (PSCs) as an inorganic hole-transporting material (HTM). A power conversion efficiency (PCE) of 12.8% was achieved for the PSCs using CISe QDs as the HTM, which is the highest value reported to date for devices with a Cu-based chalcopyrite semiconductor as HTM. More importantly, the stability of PSCs with CISe QDs was significantly improved compared with that of the devices using spiro-OMeTAD as the HTM. These results demonstrate that CISe QDs are a promising inorganic HTM for PSCs with long-term stability and low cost.

Promoting the Hole Extraction with Co3O4 Nanomaterials for Efficient Carbon‐Based CsPbI2Br Perovskite Solar Cells

Carbon‐based perovskite solar cells (PSCs) have gathered much attention due to their excellent thermal stability and low cost. However, the typically used hole‐conductor‐free PSCs based on carbon electrodes show the worst performance due to the serious charge recombination at the perovskite/carbon interface. In this work, the efficient and stable carbon‐based CsPbI2Br PSCs using Co3O4 as the hole transport material (HTM) are fabricated and their photoelectric properties are systematically investigated. It is found that the Co3O4 inorganic HTM effectively promotes photo‐generated charges separation and extraction, and suppresses charge recombination at the CsPbI2Br/carbon electrode interface, resulting in the improved photovoltaic performance. At the optimal Co3O4 concentration, the carbon‐based CsPbI2Br PSCs achieve the maximum efficiency of 11.21% with a negligible J–V hysteresis. This work provides a novel strategy to fabricate efficient and stable all‐inorganic PSCs.

Dopant-free molecular hole transport material that mediates a 20% power conversion efficiency in a perovskite solar cell

Organic molecular hole-transport materials (HTMs) are appealing for the scalable manufacture of perovskite solar cells (PSCs) because they are easier to reproducibly prepare in high purity than polymeric and inorganic HTMs.

Comparative Study of Lead-Free Perovskite Solar Cells Using Different Hole Transporter Materials

In recent years, there has been an unprecedented rise in the performance of metal halide perovskite solar cells. The lead-free perovskite solar cells (PSCs) have drawn much research interest due to the Pb toxicity of the lead halide perovskite. CH3NH3SnI3 is a viable alternative to CH3NH3PbX3. In this work, we designed a tin-based perovskite simulated model with the novel architecture of (TCO)/buffer (TiO2)/absorber (Perovskite)/hole transport material (HTM) and analyzed using the solar cell capacitance simulator (SCAPS-1D), which is well adapted to study the photovoltaic architectures. In the paper, we studied the influences of perovskite thickness and the doping concentration on the solar cell performance through theoretical analysis and device simulation. The results are indicating that the lead-free CH3NH3SnI3 is having the greatpotential to be an absorber layer with suitable inorganic hole transport materials like CuI (PCE: 23.25%), Cu2O (PCE: 19.17%), organic hole transport materials like spiro-OMETAD (PCE: 23.76%) and PTAA (PCE: 23.74%) to achieve high efficiency. This simulation model will become a good guide for the fabrication of high efficiency tin-based perovskite solar. The results show that the lead-free CH3NH3SnI3 is a potential environmentally friendly solar cells with high efficiency.

Progress on the Synthesis and Application of CuSCN Inorganic Hole Transport Material in Perovskite Solar Cells.

P-type wide bandgap semiconductor materials such as CuI, NiO, Cu2O and CuSCN are currently undergoing intense research as viable alternative hole transport materials (HTMs) to the spiro-OMeTAD in perovskite solar cells (PSCs). Despite 23.3% efficiency of PSCs, there are still a number of issues in addition to the toxicology of Pb such as instability and high-cost of the current HTM that needs to be urgently addressed. To that end, copper thiocyanate (CuSCN) HTMs in addition to robustness have high stability, high hole mobility, and suitable energy levels as compared to spiro-OMeTAD HTM. CuSCN HTM layer use affordable materials, require short synthesis routes, require simple synthetic techniques such as spin-coating and doctor-blading, thus offer a viable way of developing cost-effective PSCs. HTMs play a vital role in PSCs as they can enhance the performance of a device by reducing charge recombination processes. In this review paper, we report on the current progress of CuSCN HTMs that have been reported to date in PSCs. CuSCN HTMs have shown enhanced stability when exposed to weather elements as the solar devices retained their initial efficiency by a greater percentage. The efficiency reported to date is greater than 20% and has a potential of increasing, as well as maintaining thermal stability.

Design of an Inorganic Mesoporous Hole-Transporting Layer for Highly Efficient and Stable Inverted Perovskite Solar Cells.

The unstable feature of the widely employed organic hole-transporting materials (HTMs) (e.g., spiro-MeOTAD) significantly limits the practical application of perovskite solar cells (PSCs). Therefore, it is desirable to design new structured PSCs with stable HTMs presenting excellent carrier extraction and transfer properties. This work demonstrates a new inverted PSC configuration. The new PSC has a graded band alignment and bilayered inorganic HTMs (i.e., compact NiOx and mesoporous CuGaO2 ). In comparison with planar-structured PSCs, the mesoporous CuGaO2 can effectively extract holes from perovskite due to the increased contact area of the perovskite/HTM. The graded energy alignment constructed in the ultrathin compact NiOx , mesoporous CuGaO2 , and perovskite can facilitate carrier transfer and depress charge recombination. As a result, the champion device based on the newly designed mesoscopic PSCs yields a stabilized efficiency of ≈20%, which is considered one of the best results for inverted PSCs with inorganic HTMs. Additionally, the unencapsulated PSC device retains more than 80% of its original efficiency when subjected to thermal aging at 85 °C for 1000 h in a nitrogen atmosphere, thus demonstrating superior thermal stability of the device. This study may pave a new avenue to rational design of highly efficient and stable PSCs.

A Review of Inorganic Hole Transport Materials for Perovskite Solar Cells

AbstractThis review presents various hole transport layers (HTLs) employed in perovskite solar cells (PSCs) in pursuing high power conversion efficiency (PCE) and functional stability. The PSCs have achieved high PCE (over 23%, certified by NREL) and more efforts have been devoted into research for stability enhancement. Inorganic HTLs become a popular choice as selective contact materials because of their intrinsic chemical stability and low cost. HTLs and electron transport layers (ETLs) are critical components of PSCs due to the requirement to create charge collection selectivity. Herein the authors provide an overview on inorganic HTLs synthesis, properties, and their application in various PSCs for both mesoporous and planar architectures. Inorganic HTLs with appropriate properties, such as proper energy level and high carrier mobility, can not only assist with charge transport, but also improve the stability of PSCs under ambient conditions. The importance of interfacial chemistry and interfacial charge transport is further addressed to understand the underlying mechanism of related degradation and carrier dynamic. It is expected that the success of the inorganic HTL in PSCs can stimulate further research and bring real impact for future photovoltaic technologies.

Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

This article reviews various dopant‐free hole transporting materials (HTMs) used in perovskite solar cells (PSCs) in three main categories including inorganic, polymeric, and small molecule HTMs. PSCs have undergone rapid progress, achieving power conversion efficiencies (PCEs) above 22%. With their low production cost and high efficiencies, PSCs are considered promising next‐generation solar cell technology. In all developed architectures for PSCs, including planar and mesoscopic with conventional and inverted structures, HTMs play a significant role in determining the photovoltaic performance of PSCs. Using p‐type dopants, however, is considered a common strategy to increase the hole conductivity of HTM, which is usually compensated by a more complicated fabrication procedure, higher production costs, and lower stability of PSC. Although several reviews on HTMs have been published, progress on dopant free HTMs needs to be reviewed and analyzed. Here, a review covering most of the published reports on dopant‐free HTMs is presented, and the device structure and fabrication method, HTM layer deposition techniques, and the efficiency and the stability of PSCs are addressed during discussions in each main category. Finally, an outlook on stability and PCE growth in PSCs based on dopant‐free HTMs is presented.

Inorganic Materials as Hole Selective Contacts and Intermediate Tunnel Junction Layer for Monolithic Perovskite‐CIGSe Tandem Solar Cells

AbstractIn order to surpass the theoretical limitation defined by the Shockley–Queisser equation for photovoltaic solar cells, multijunction devices are needed. Monolithic perovskite‐Cu(In, Ga)(Se, S)2 (CIGSe) tandem solar cells have recently become a hot research topic in photovoltaics because of the emergence of perovskite solar cells with high power conversion efficiency and the development of thin film chalcopyrite CIGSe solar cells with tunable bandgap and low cost manufacturing processes. In this review, some p‐type wide bandgap semiconductors are investigated as intermediate inorganic hole transport materials (IIHTM) and components of a tunnel junction in monolithic perovskite‐CIGSe tandem solar cells, which meet the requirements of band alignment and low‐temperature deposition process. The authors focus on designing a tandem configuration including band alignment, current matching, and optical management, describing some potential candidates of IIHTM owing to their successful implementation in single junction perovskite solar cells and the possibility of application in intermediate layers for tandem devices. Recent progress in the development of inorganic hole conductors is highlighted, and also some of the authors' work on IIHTM and their applications are presented. Finally, future research directions for IIHTM layers and monolithic perovskite‐CIGSe tandem solar cells are presented, with an aim to achieve higher photovoltaic performance than current devices.