Materials For Perovskite Solar Cells Research Articles

Enhanced Performance of Perovskite Solar Cell via Controlling Layer Thickness

In this study, Perovskite material methylammonium lead iodide (CH3NH3PbI3) was successfully fabricated using a two-step sequential solution deposition method. The precursor solution of lead iodide was first spin-coated, followed by immersing the film into a solution of CH3NH3I to form the Perovskite layer. The Perovskite material was then successfully applied as a light-harvesting material in Perovskite solar cells. The power conversion efficiency of the devices was optimized by varying TiO2 blocking layer, TiO2 mesoporous layer, and perovskite capping layer thickness. The best Perovskite solar cell exhibits a power conversion efficiency of 7.72% with a short-circuit photocurrent density JSC of 17.26 mA/cm2, an open-circuit photovoltage VOC of 0.94 V, and a fill factor of 47.6%; with the thicknesses of TiO2 blocking layer, TiO2 mesoporous layer, and perovskite capping layer of 100 nm, 200 nm, and 400 nm, respectively. The results show that Perovskite material has potential for solar cell application.

Low-temperature solution-processed Mg: NiOx hole transport layers for formal (n-i-p) perovskite solar cells

NiOx is one of the most promising inorganic hole transport materials for perovskite solar cells. However, lots of fabrication methods refer to NiOx are limited in n-i-p type perovskite solar cells. Because the deposition procedure of NiOx film such as polar solvents and high temperature process is seriously incompatible with perovskite light-absorption underlayers. In this work, highly crystalline NiOx nanocrystals are prepared using solvothermal method under the presence of long-chain oleylamine molecules. The resulted NiOx nanocrystals can be easily dispersed in weak-polar toluene and form films on perovskite layer without annealing procedure. The n-i-p type device with NiOx hole transport layer achieves an efficiency of 10.34%. Later, Mg2+ with different molar ratios are incorporated into the NiOx nanocrystals. It is found that introducing a certain amount of Mg2+ benefits to improve the ratio of Ni3+/Ni2+, thereby changing the work function and increasing the hole conductivity. As a result, the n-i-p type device with Mg-NiOx hole transport layer yields an improved efficiency of 12.41%.

Multifunctional Narrow Band Gap Terpolymer-Enabled High-Performance Dopant-Free Perovskite and Additive-Free Organic Solar Cells with Long-Term Stability.

The optoelectronic devices endowing multifunctionality while utilizing a single low-cost material have always been challenging. For this purpose, we adopted a random ternary copolymerization strategy for designing two terpolymers, namely TP-0.8-EG and TP-0.8-TEG comprising a benzothiadiazole (BT)-benzo[1,2-b:4,5-b']dithiophene-diketopyrrolo[3,4-c]pyrrole (A1-π-D-π-A2) backbone. The figure of merits of the narrow band gap TP-0.8-EG terpolymer include deepened frontier energy levels, high hole mobility, better film formability, enriched multifunctionality, and passivation capability. Accordingly, the suitable electronic properties of TP-0.8-EG revealed that it can function as a dopant-free hole-transporting material in perovskite solar cells (PSCs) as well as the third component in organic solar cells (OSCs). Remarkably, TP-0.8-EG outperforms by exhibiting a higher power conversion efficiency (PCE) of 20.9% over TP-0.8-TEG (PCE of 18.3%) and BT-UF (PCE of 14.6%) in dopant-free PSCs. Interestingly, TP-0.8-EG fabricated along with PM6:Y7 displayed a high PCE of 16.52% in ternary OSCs. Also, TP-0.8-EG established good device storage stabilities (85 and 83% of their initial PCEs for 1200 and 500 h) in dopant-free PSC as well as OSC devices. Notably, the devices with TP-0.8-EG showed excellent thermal and moisture stabilities. To the best of our knowledge, A1-π-D-π-A2 terpolymer performing both in PSCs and OSCs with decent efficiencies and good device stabilities is a rare scenario.

Solution-processed pristine metal oxides as electron-transporting materials for perovskite solar cells

In recent years, perovskite material-based photovoltaic devices have attracted great attention of researchers because of an expeditious improvement in their efficiency from 3.8% to over 25%. The electron transport layer (ETL), which functions for the extraction and transportation of photogenerated electrons from active perovskite material to the electrodes, is a vital part of these perovskite solar cells (PSCs). The optoelectronic properties of these electron transport layer materials also have an impact on the performance of these perovskite solar cells, and for commercialized flexible perovskite solar cells, low-temperature and solution-processable electron transport layers having high stability and suitable optoelectronic properties are needed. In this regard, the solution-processable films of different metal oxides have been largely investigated by many research groups. So, this review summarizes the optoelectronic properties of the different metal oxide-based electron transport layers and the development in the performance of the perovskite solar cells, which have solution-processable metal oxides as electron transport layers.

Performance Optimization of Inorganic Cs2TiBr6 Based Perovskite Solar Cell via Numerical Simulation

Perovskite solar cells (PSCs) are considered highly efficient and hold great potential for next‐generation photovoltaic devices due to their excellent properties. However, there are some challenges that hinder their mass production, such as toxicity in lead‐based PSCs, nonstability, and high manufacturing costs. This study aims to address these challenges by proposing a device modeling approach to optimize the design of highly efficient lead‐free cesium titanium bromide (Cs2TiBr6) perovskite solar cells. Cs2TiBr6‐based perovskite solar cells have low performance due to the lack of suitable electron and hole transport layers. Therefore, this study utilizes numerical simulations in SCAPS‐1D to investigate the effect of different parameters, including the doping density of optimized hole and electron transport layers, the thickness of the absorber layer, the NA/ND of the absorption layer, and the defect concentration. The study models six different device structures with different hole transport layerss. However, an optimized novel structure device Se/CuSbS2/Cs2TiBr6/IZGO/FTO/Glass has been proposed, with a theoretical power conversion efficiency of 29.19%. This device has a VOC of 1.33 V, JSC of 24.28 mA cm−2, and FF of 90.46%. Overall, this study demonstrates the potential of Cs2TiBr6 as a promising material for perovskite solar cells, providing a nontoxic, green renewable energy solution for the future.

Triphenylimidazole substituted D-π-D porphyrin based dopant-free hole transport materials for perovskite solar cells

Hole-transport materials (HTMs) contribute an important function in perovskite solar cells (PSCs) for achieving favourable photovoltaic performance with durability. In this work, we designed and synthesized a series of porphyrin based hydrophobic HTMs based on donor-π-donor (D-π-D) tactic in which triphenylimidazole as donor and either free-base porphyrin (H2LD) or metalloporphyrin (Cu, CuLD or Zn, ZnLD) as π-spacer for PSCs. All three HTMs were characterized by a variety of spectroscopic and electrochemical methods. Optical and electrochemical properties propose that the highest occupied molecular orbital (HOMO) energy levels were healthily aligned with the valence band of MAPbI3 perovskite. Among these HTMs, CuLD exhibited higher hole mobility of 7.39 × 10-5 cm2V-1s-1, when compared to ZnLD 5.77 × 10-5 cm2V-1s-1, and H2LD 2.7 × 10-5 cm2V-1s-1. We fabricated PSCs with these HTMs and among them the CuLD based PSCs showed highest power conversion efficiency of 12.44%. The better PCE for the PSCs fabricated with CuLD could be attributed to the higher conductivity and better hole mobility which could be correlated to the better film formation.

Insights into the photovoltaic properties of indium sulfide as an electron transport material in perovskite solar cells

According to recent reports, planar structure-based organometallic perovskite solar cells (OPSCs) have achieved remarkable power conversion efficiency (PCE), making them very competitive with the more traditional silicon photovoltaics. A complete understanding of OPSCs and their individual parts is still necessary for further enhancement in PCE. In this work, indium sulfide (In2S3)-based planar heterojunction OPSCs were proposed and simulated with the SCAPS (a Solar Cell Capacitance Simulator)-1D programme. Initially, OPSC performance was calibrated with the experimentally fabricated architecture (FTO/In2S3/MAPbI3/Spiro-OMeTAD/Au) to evaluate the optimum parameters of each layer. The numerical calculations showed a significant dependence of PCE on the thickness and defect density of the MAPbI3 absorber material. The results showed that as the perovskite layer thickness increased, the PCE improved gradually but subsequently reached a maximum at thicknesses greater than 500 nm. Moreover, parameters involving the series resistance as well as the shunt resistance were recognized to affect the performance of the OPSC. Most importantly, a champion PCE of over 20% was yielded under the optimistic simulation conditions. Overall, the OPSC performed better between 20 and 30 °C, and its efficiency rapidly decreases above that temperature.

Enhanced photostability of multication lead halide perovskites through the use of azaadamantane-based modifiers

Complex lead halides incorporating simultaneously a few univalent cations such as cesium (Cs+), methylammonium (MA+) and formamidinium (FA+) represent highly promising materials for perovskite solar cells, delivering record-high power conversion efficiencies. Unfortunately, these materials demonstrate insufficient stability, which limits their practical implementation; therefore, improving the photochemical and thermal stability of multication lead halide perovskites is an urgent task that needs to be addressed to achieve sufficiently long operational lifetimes of perovskite solar cells to facilitate their commercial real-life applications. Herein, we present a comparative study of two azaadamantane-based molecular modifiers as stabilizing additives for Cs0.10MA0.15FA0.75PbI3 and Cs0.12FA0.88PbI3 perovskite formulations. An iodide of N-methylated 1,3,5,7-tetraazaadamantane known as urotropine (MAdI) showed a modest stabilizing effect in Cs0.10MA0.15FA0.75PbI3, though it stabilized effectively Cs0.12FA0.88PbI3. On the contrary, 4,6,10-trihydroxy-3,5,7-trimethyl-1,4,6,10-tetraazaadamantane hydrochloride (NAdCl) strongly enhanced the stability of both lead halide perovskites and prevented the formation of metallic lead Pb0 as a photolysis product. Different stabilizing effects caused by MAdI and NAdCl were related to their different localization within the perovskite films, as evidenced by nanoscale infrared (IR) s-SNOM microscopy. Density functional theory (DFT) calculations confirmed the enhanced stability granted by NAdCl by demonstrating a much higher adsorption energy towards undercoordinated lead atoms on the surface of the perovskite. Finally, the optimal molecular modification of Cs0.10MA0.15FA0.75PbI3 and Cs0.12FA0.88PbI3 films with azaadamantanes made them completely tolerant to light and heat within at least 5000 and 16 000 h of aging, thus setting new perovskite stability records and presenting the newly-developed material formulations as highly promising absorbers for efficient and stable perovskite solar cells.

Advances on the Application of Wide Band-Gap Insulating Materials in Perovskite Solar Cells.

In recent years, the development of perovskite solar cells (PSCs) is advancing rapidly with their recorded photoelectric conversion efficiency reaching 25.8%. However, for the commercialization of PSCs, it is also necessary to solve their stability issue. In order to improve the device performance, various additives and interface modification strategies have been proposed. While, in many cases, they can guarantee a significant increase in efficiency, but not ensure improved stability. Therefore, materials that improve the device efficiency and stability simultaneously are urgently needed. Some wide band-gap insulating materials with stable physical and chemical properties are promising alternative materials. In this review, the application of wide band-gap insulating materials in PSCs, including their preparation methods, working roles, and mechanisms are described, which will promote the commercial application of PSCs.

Novel Materials in Perovskite Solar Cells: Efficiency, Stability, and Future Perspectives.

Solar energy is regarded as the finest clean and green energy generation method to replace fossil fuel-based energy and repair environmental harm. The more expensive manufacturing processes and procedures required to extract the silicon utilized in silicon solar cells may limit their production and general use. To overcome the barriers of silicon, a new energy-harvesting solar cell called perovskite has been gaining widespread attention around the world. The perovskites are scalable, flexible, cost-efficient, environmentally benign, and easy to fabricate. Through this review, readers may obtain an idea about the different generations of solar cells and their comparative advantages and disadvantages, working mechanisms, energy alignment of the various materials, and stability achieved by applying variable temperature, passivation, and deposition methods. Furthermore, it also provides information on novel materials such as carbonaceous, polymeric, and nanomaterials that have been employed in perovskite solar in terms of the different ratios of doping and composite and their optical, electrical, plasmonic, morphological, and crystallinity properties in terms of comparative solar parameters. In addition, information on current trends and future commercialization possibilities of perovskite solar have been briefly discussed based on reported data by other researchers.

Aggregation-induced Emission Materials for High-efficiency Perovskite Solar Cells.

The perovskite solar cells (PSCs) with high efficiency and stability are in great demand for commercial applications. Although the remarkable photovoltaic feature of perovskite layer plays a great role in improving the PCE of PSCs, the inevitable defects and poor stability of perovskite, etc. are the bottleneck and restrict the commercialization of PSCs. Herein, a review provides a strategy of applying aggregation-induced emission (AIE) molecules, containing passivation functional groups and distinct AIE character, which serves as the alternative materials for fabricating high-efficiency and high-stability PSCs. The methods of introducing AIE molecules to PSCs are also summarized, including additive engineering, interfacial engineering, hole transport materials and so on. In addition, the functions of AIE molecule are discussed, such as defects passivation, morphology modulation, well-matched energy level, enhanced stability, hole transport ability, carrier recombination suppression. Finally, the conclusions are offered and further research trend for high performance PSCs based on AIE materials is proposed.

CsPbI3 Based All‐Inorganic Perovskite Solar Cells: Further Performance Enhancement of the Electron Transport Layer‐Free Structure from Device Simulation

Abstract Cesium lead iodide (CsPbI3) has attracted a great deal of attention as an absorption layer material for perovskite solar cells (PSCs) with high stability and suitable band gap (1.72 eV). In response to the problems of defect‐induced nonradiative compounding and voltage loss caused by the common perovskite layer, the common strategies of interfacial engineering, altering crystal equivalence, and other modifications involve more complex processes and higher fabrication costs. In order to simplify the process and save costs, this work has omitted the electron transport layer (ETL), while still maintaining a high power conversion efficiency (PCE). This work has simulated PSCs with CsPbI3 (electron transport layer free) and have matched Cu2O as the most suitable hole transport layer (HTL) material. By simulating and optimizing the thickness and defect density of perovskite absorption layer and the defect density of interface defect layer (IDL1, IDL2), and determining the most suitable operating temperature, the PCE of the device can reach 18.8%, which is consistent with the experimental data. The asymmetric effect of the interface defect layer obtained in this work is similar to previous research reports. This research provides an economical solution for high‐performance inorganic perovskite solar cells.

Development of a new hole transport material for perovskite solar cells

N,N-di(4-methoxyphenyl)amino-9,9′-spirobifluorene (spiro-OMeTAD) is a widely used hole transport layer (HTL) material for emerging lead halide hybrid perovskite solar cells (PSCs). Finding alternative HTL materials is required for the future development of more efficient and stable PSCs. Here, we developed a new HTL material of N2,N2,N,7N7-tetrakis(4-methoxyphenyl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diamine (TBTD). Chemically doped TBTD provided better hole extraction in PSCs than chemically doped spiro-OMeTAD due to higher electrical conductivity and a more suitable hole transport energy level. Thus, PSCs with the TBTD HTL showed higher power conversion efficiency (∼21%) than spiro-OMeTAD HTL (∼19%). The operational stability of TBTD-based PSCs was similar to that of spiro-OMeTAD-based PSCs. The findings discussed in this study will aid in the future development of high-performance PSCs.

Economical and Environmentally Friendly Organic hydrazone Derivatives Characterized by a Heteroaromatic Core as Potential Hole Transporting Materials in Perovskite Solar Cells

AbstractA series of organic electron‐rich π‐bridged symmetric hydrazones, composed of two donor moieties connected through a thiophene‐ or a pyrrole‐based π‐spacer, has been synthesized as a suitable alternative to 2,2’,7,7’‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9’‐spirobifluorene (Spiro‐OMeTAD), considered the benchmark hole transporting material (HTM) in perovskite solar cells (PSCs). The cheap synthetic protocol is suitable for potential large‐scale production. All the compounds were characterized, showing good energy levels alignments with the perovskite and very close energy levels to the Spiro‐OMeTAD. Furthermore, computational analysis confirmed the electrochemical trend observed. The costs of synthesis were estimated, as well as the produced waste to synthesise the final HTMs, underlining the low impact of these compounds on the environment with the respect to Spiro‐OMeTAD. Overall, the relevant electrochemical properties and the low cost of the synthetic approaches allow these compounds to be a greener and easy‐to‐synthesize alternative to the Spiro‐OMeTAD for industrial development of PSCs.

Isolating the Oxygen Adsorption Defects on Sputtered Tin Oxide for Efficient Perovskite Solar Cells

Tin oxide (SnO2) is the most commonly used electron transport material for perovskite solar cells (PSCs). Various techniques have been applied to deposit tin dioxide, including spin-coating, chemical bath deposition, and magnetron sputtering. Among them, magnetron sputtering is one of the most mature industrial deposition techniques. However, PSCs based on magnetron-sputtered tin oxide (sp-SnO2) have a lower open-circuit voltage (Voc) and power conversion efficiency (PCE) than those prepared by the mainstream solution method. This is mainly due to the oxygen-related defects at the sp-SnO2/perovskite interface, and traditional passivation strategies usually have little effect on them. Herein, we successfully isolate the oxygen adsorption (Oads) defects located on the surface of sp-SnO2 from the perovskite layer using a PCBM double-electron transport layer. This isolation strategy effectively suppresses the Shockley-Read-Hall recombination at the sp-SnO2/perovskite interface, which results in an increase in the Voc from 0.93 to 1.15 V and an increase in PCE from 16.66 to 21.65%. To our knowledge, this is the highest PCE achieved using a magnetron-sputtered charge transport layer to date. The unencapsulated devices maintain 92% of their initial PCE after storage in air with a relative humidity of 30-50% after 750 h. We further use the solar cell capacitance simulator (1D-SCAPS) to confirm the effectiveness of the isolation strategy. This work highlights the application prospect of magnetron sputtering in the field of perovskite solar cells and provides a simple yet effective way to tackle the interfacial defect issue.

Hydrophobic 4-(isopropylbenzyl)oxy-substituted metallophthalocyanines as a dopant-free hole selective material for high-performance and moisture-stable perovskite solar cells

Dopant-free hole-transporting materials (HTMs) are necessary to overcome the instability for perovskite solar cells (PSCs) originating from conventional HTMs such as spiro-OMeTAD requiring hygroscopic dopants for future commercialization. Herein, a series of dopant-free HTMs based on peripherally 4-(isopropylbenzyl)oxy-substituted phthalocyanines with different core metals (EG-pZn1, EG-pCu1, and EG-pNi1) are designed and introduced as a hole-transport layer in PSCs for the first time. The introduction of hydrophobic bulky 4-(isopropylbenzyl)oxy moieties to the phthalocyanine structure favors excellent moisture-resistant effect, and good solubility, as well as suppression of charge recombination in PSCs. Three HTMs-based cells afford an impressive efficiency of 17.60% (EG-pNi1), 16.45% (EG-pCu1), and 15.83% (EG-pZn1) with the character of hysteresis-free. More importantly, while EG-pNi1 and EG-pCu1 HTL-based devices can effectively protect perovskite film from moisture which degraded to only 10% of its initial efficiency under humidity level (60–65%) after a period of 20 days, unexpectedly, ∼30% loss of initial efficiency has been observed in EG-pZn1 HTM based devices under the same conditions. Furthermore, EG-pNi1-based devices also show excellent thermal stability, maintaining 95% initial efficiency after aging for 20 days at 85 °C. These results demonstrate the role of peripherally substituted hydrophobic 4-(isopropylbenzyl)oxy group in HTMs on photovoltaic performance and moisture-/thermal-stability of PSCs and its potential in reasonable and effective ways of industrial commercialization of PSCs.

Small carbazole-based molecules as hole transporting materials for perovskite solar cells

In this study, six small carbazole-based molecules are investigated for usage as hole transport materials (HTMs) in perovskite solar cells. Among these compounds, two molecules based on 9-(4-(thiophen-2-yl)phenyl)-9H-carbazole thiophene-phenyle and carbazole (M1 and M2) were already synthesized, and four new molecules are designed by substituting carbazole, in positions 3,6 and 2,7, with methoxyphenyl (P1 and P2) and dimethoxyphenylamine (E1 and E2). Theoretical methods used in the calculations included density functional theory and time-dependent density functional theory. FMOs of all under-probe molecules are well positioned to ensure accurate alignment and prevent charge recombination at the perovskite material interface. The molecules' absorbance in the area below 404 nm shows that HTMs cannot compete with perovskite materials in an inverted configuration of a device. Reorganization energies indicate that M1, P1,2 and E1,2 are more favourable to be HTM, while M2 shows a favourable electron transfer; it can be used as an electron transfer material (ETM). The results demonstrate that hole-electron couples can easily separate for any under-exanimated molecules, simplifying hole transport and enhancing the short-circuit (JSC). Additionally, DMPA-based molecules (E1,2) may display chemical instability because of their poor hardness and the local distribution of charge in electrostatic potential maps.

Incorporation of carbon nanotubes in hole transport materials for perovskite solar cells

ABSTRACT Many loss processes in perovskite solar cells (PSCs) take place at interfaces. One effective mitigation strategy is introducing carbon derivatives at the interface of the charge transport layers with the halide perovskite absorber and/or with the contacts. In this work, single-walled carbon nanotubes are incorporated into the hole transporting material (HTM), either as composites or as a separate layer on top of the HTM. Both organic and inorganic hole transport materials are studied to validate this approach for different types of HTMs. It is shown that the CNTs facilitate charge transport from perovskite to the back contact, regardless of the HTM used. The use of CNTs results in an increase in a significant increase in short circuit current and power conversion efficiency. This study illustrates how SWCNTs can be utilised to improve the properties of a wide range of HTMs, which will pave the way for more efficient and PSCs.

Dopant-Free Pyrrolopyrrole-Based (PPr) Polymeric Hole-Transporting Materials for Efficient Tin-Based Perovskite Solar Cells with Stability Over 6000h.

A new set of pyrrolopyrrole-based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) is synthesized and explored as hole-transporting materials (HTMs) for Sn-based perovskite solar cells (TPSCs). Three bithiophenyl spacers bearing the thioalkylated hexyl (SBT-6), thioalkylated tetradecyl (SBT-14), and tetradecyl (BT-14) chains are utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs are fabricated using PPr-SBT-14 as HTMs through a two-step approach by attaining a power conversion efficiency (PCE) of 7.6% with a remarkable long-term stability beyond 6000 h, which has not been reported elsewhere for a non-PEDOT:PSS-based TPSC. The PPr-SBT-14 device is stable under light irradiation for 5 h in air (50% relative humidity) at the maximum power point (MPP). The highly planar structure, strong intramolecular S(alkyl)···S(thiophene) interactions, and extended π-conjugation of SBT enable the PPr-SBT-14 device to outperform the standard poly(3-hexylthiophene,-2,5-diyl (P3HT) and other devices. The longer thio-tetradecyl chain in SBT-14 restricts molecular rotation and strongly affects the molecular conformation, solubility, and film wettability over other polymers. Thus, the present study makes a promising dopant-free polymeric HTM model for the future design of highly efficient and stable TPSCs.

Defect and doping concentration study with series and shunt resistance influence on graphene modified perovskite solar cell: A numerical investigation in SCAPS-1D framework

Perovskite solar cells (PSCs) have the potential to be highly efficient, low-cost next-generation solar cells. By raising open circuit voltage (Voc), the interfacial recombination kinetics can further improve device performance. In this study, we used simulation concept to elucidate the influence of using graphene as a surface passivation material in perovskite solar cells. Graphene works well as an interlayer to promote hole extraction and reduce interfacial recombination. In order to evaluate the effect of graphene in PSCs, the simulation was done in the SCAPS-1D framework to compare the performance of a device with and without graphene. Three interface layers were included to the model: TiO2/MAPbI3, MAPbI3/Graphene, and Graphene/Spiro-OMeTAD, in order to account for the impacts of interface defect density on device performance. The impacts of absorber doping concentration, absorber defect density, ETL doping concentration, HTL doping concentration, series resistance, and shunt resistance were also evaluated for the modelled PSC. Without any optimization, the control device with power conversion efficiency (PCE) of 20.677% was outperformed by the graphene-modified device with PCE of 20.911%. This difference is mostly due to the lower recombination losses and more effective suppression of interfacial non-radiative recombination. With optimization, the modified graphene-based device has a PCE of 26.667%. This result shows an enhancement of ∼1.28 times over that of the pristine graphene-based device. The outcomes have opened the way for the development of cost-effective and comparable state-of-the-art, high-efficiency perovskite solar cells with graphene interlayer by eliminating defects and managing non-radiative recombination.