HTM-free Perovskite Solar Cells Research Articles

Regulation interfacial energy by reducing the Young’s modulus of perovskite film in carbon-based HTM free MAPbI3 perovskite solar cell

In ambient air, a long-chain dodecafluorosuberic acid (DFSA) with lower Young’s modulus was introduced to improve the mechanical compatibility of perovskite/carbon interface. Firstly, the carbonyl groups CO and F– in DFSA can passivate the intrinsic defects of perovskite, the DFSA effectively reduces the Young’s modulus of the perovskite and mitigates residual stress generated during perovskite annealing procedure. Most importantly, DFSA significantly enhances the Young’s modulus compatible degree between DFSA-CH3NH3PbI3 (DFSA-MAPbI3, 35.8 GPa) and carbon (6.3 GPa), alleviating the interfacial stress concentration. Based on quantitatively analysis, interfical crack driving energy (Gd) is reduced from 0.63 to 0.43 J m−2, while the adhesive fracture energy (Ga) is increased from 0.47 to 0.54 J m−2, which reduces the probability of crack propagation and ductile delamination, and is conducive to the extraction and transmission of photogenerated carrior. This was also verified in finite element simulations. Finally, the photoelectric conversion efficiency (PCE) of the organic-inorganic hybrid perovskite (MAPbI3) PSC device is improved from 10.27 % to optimal 14.12 %. After service at room temperature with relative humidity (RH) of 50–55 % and high temperature of 85 °C for 720 h, the original efficiency is maintained at 72 % and 89 %, respectively.

Enhanced performance of HTM-free perovskite solar cells with free-standing carbon electrode via surface treatment and conductive support

This study explores the optimization of hole transport material (HTM)-free perovskite solar cells featuring laminated free-standing carbon film as a back electrode. Surface treatment of perovskite film using different types of solvent (chlorobenzene, toluene, and ethyl acetate) was carried out to improve the electrical contact at the carbon/methylammonium lead iodide interface. Overall, the surface treatment improved mechanical adhesion between the perovskite and carbon film. The conductivity of the free-standing carbon electrode was further improved by attaching the carbon film to various types of conductive support. Our results show that the selection of both solvents used during surface treatment and the type of conductive substrate has a considerable impact on the resulting performance, wherein all modifications gave rise to substantial improvement over the benchmark unmodified carbon electrode. A power conversion efficiency (PCE) of 7.74% was achieved by the perovskite solar cell with laminated carbon electrode on Al foil combined with the application of chlorobenzene as surface treatment, demonstrating a tremendous increase in performance compared to that of untreated free-standing carbon electrode that produced PCE less than 1%. The main contributor to the improved performance is presumably due to the low carrier recombination rate and improved charge carrier extraction as implied by the electro-impedance spectroscopy and photoluminescence analysis. This work demonstrates a facile approach for resolving the challenges in developing low-cost HTM-free perovskite solar cells with a free-standing carbon film electrode.

Strengthened Interficial Adhesive Fracture Energy by Young's Modulus Matching Degree Strategy in Carbon-Based HTM Free MAPbI3 Perovskite Solar Cell with Enhanced Mechanical Compatibility.

Carbon-based hole transport layer-free perovskite solar cells (PSCs) based on methylammonium lead triiodide (MAPbI3 ) have become one of the research focus due to low cost, easy preparation, and good optoelectronic properties. However, instability of perovskite under vacancy defects and stress-strain makes it difficult to achieve high-efficiency and stable power output. Here, a soft-structured long-chain 2D pentanamine iodide (abbreviated as "PI") is used to improve perovskite quality and interfacial mechanical compatibility. PI containing CH3 (CH2 )4 NH3 + and I- ions not only passivate defects at grain boundaries, but also effectively alleviate residual stress during high temperature annealing via decreasing Young's modulus of perovskite film. Most importantly, PI effectively increases matching degree of Young's modulus between MAPbI3 (47.1GPa) and carbon (6.7GPa), and strengthens adhesive fracture energy (Gc ) between perovskite and carbon, which is helpful for outward release of nascent interfacial stress generated under service conditions. Consequently, photoelectric conversion efficiency (PCE) of optimal device is enhanced from 10.85% to 13.76% and operational stability is also significantly improved. 83.1% output is maintained after aging for 720h at room temperature and 25-60% relative humidity (RH). This strategy of regulation from chemistry and physics provides a strategy for efficient and stable carbon-based PSCs.

Impact of hole transport material on perovskite solar cells with different metal electrode: A SCAPS-1D simulation insight

The high efficiency and low cost of production of perovskite solar cells (PSCs) based on organic-inorganic halides have attracted the attention of researchers. However, due to the intricacy in the synthesis of Spiro-OMeTAD and the high cost of gold (Au) utilized as the back contact (BC), have affected its viability for commercialization. In this present study, a simulation was performed with and without HTM utilizing different metal contacts (Ag, Cr, Cu, Au, Ni and Pt). SCAPS-1D, a software program in one dimension, was used to conduct the simulation. A systematic analysis was done to determine how the metal back contact's work functions affected the PSC both with and without HTM. The outcomes demonstrate that the PSCs' photovoltaic performance is significantly influenced by the metal contact's work function (WF). The best metal contact for HTM and HTM-free devices was Pt, with a metal work function of 5.65 eV. The initial power conversion efficiencies (PCEs) for the two configurations were 26.229% for HTM-free and 25.608% for HTM-based device. A number of parameters, including absorber thickness, interface defect density, and electron transport material (ETM) thickness, were varied to obtain optimal values of 0.8 μm for both HTM and HTM-free PSCs, 1005 cm−2 for both HTM and HTM-free PSCs, and 0.01 μm for both HTM and HTM-free PSCs. These values were then used to simulate the final HTM and HTM-free devices with a PCE of 27.423%, current density (Jsc) of 27.546 mA/cm2, open circuit voltage (Voc) of 1.239 V, and fill factor (FF) of 80.347% for HTM-free whereas PCE of 26.767% with Jsc of 27.545 mA/cm2, Voc of 1.250 V, and FF of 77.733% for HTM based. These outcomes reflect outstanding enhancement of ∼1.05 and ∼1.07 times in PCE and Jsc over unoptimized cells with and without HTM.

Lead-Free Perovskite Homojunction-Based HTM-Free Perovskite Solar Cells: Theoretical and Experimental Viewpoints.

Simplifying the design of lead-free perovskite solar cells (PSCs) has drawn a lot of interest due to their low manufacturing cost and relative non-toxic nature. Focus has been placed mostly on reducing the toxic lead element and eliminating the requirement for expensive hole transport materials (HTMs). However, in terms of power conversion efficiency (PCE), the PSCs using all charge transport materials surpass the environmentally beneficial HTM-free PSCs. The low PCEs of the lead-free HTM-free PSCs could be linked to poorer hole transport and extraction as well as lower light harvesting. In this context, a lead-free perovskite homojunction-based HTM-free PSC was investigated, and the performance was then assessed using a Solar Cell Capacitance Simulator (SCAPS). A two-step method was employed to fabricate lead-free perovskite homojunction-based HTM-free PSCs in order to validate the simulation results. The simulation results show that high hole mobility and a narrow band gap of cesium tin iodide (CsSnI3) boosted the hole collection and absorption spectrum, respectively. Additionally, the homojunction's built-in electric field, which was identified using SCAPS simulations, promoted the directed transport of the photo-induced charges, lowering carrier recombination losses. Homojunction-based HTM-free PSCs having a CsSnI3 layer with a thickness of 100 nm, defect density of 1015 cm-3, and interface defect density of 1018 cm-3 were found to be capable of delivering high PCEs under a working temperature of 300 K. When compared to formamidinium tin iodide (FASnI3)-based devices, the open-circuit voltage (Voc), short-circuit density (Jsc), fill factor (FF), and PCE of FASnI3/CsSnI3 homojunction-based HTM-free PSCs were all improved from 0.66 to 0.78 V, 26.07 to 27.65 mA cm-2, 76.37 to 79.74%, and 14.62 to 19.03%, respectively. In comparison to a FASnI3-based device (PCE = 8.94%), an experimentally fabricated device using homojunction of FASnI3/CsSnI3 performs better with Voc of 0.84 V, Jsc of 22.06 mA cm-2, FF of 63.50%, and PCE of 11.77%. Moreover, FASnI3/CsSnI3-based PSC is more stable over time than its FASnI3-based counterpart, preserving 89% of its initial PCE. These findings provide promising guidelines for developing highly efficient and environmentally friendly HTM-free PSCs based on perovskite homojunction.

Numerical simulation to optimize the efficiency of HTM-free perovskite solar cells by ETM engineering

Perovskite solar cells based on carbon electrodes (c-PSCs) without a hole transport material (HTM) have gained considerable interest owing to their cost-effective and simplified structure. However, their application is constrained by a combination of low efficiency and the prevalence of electron transport materials (ETMs), e.g., TiO2, which undergo extreme temperatures during their manufacturing processes. TiO2 also has poor optoelectronic properties, such as low conductivity and mobility. Additionally, when exposed to UV light, TiO2 susceptibility to photocatalysis reduces the materials long-term stability. In present study, an HTM-free device based on FTO/TiO2/CH3NH3PbI3/carbon structure is employed and studied using a one-dimensional Solar Cell Capacitance Simulator (SCAPS-1D). Initially, the design is studied while employing inorganic ETMs, including CdZnS, WS2, WO3, ZnO, ZnOS, and ZnSe, by substituting TiO2, and the impact of each ETM on device performance is evaluated. After ETM optimization, various parameters that affect device performance, such as ETM and absorber thicknesses, doping concentrations, charge carriers mobility, and defect densities at ETM/perovskite interface, have been studied. Under optimized parameters, the design having ZnSe as ETM yields the best results with a Voc of 1.25 V, Jsc of 24.77 mA/cm2, FF of 86.29 %, and PCE of 26.76 %. The presented results thus add more promise and confidence to the ongoing quest for carbon-based, HTM-free PSCs.

SnO2@ZnO nanocomposites doped polyaniline polymer for high performance of HTM-free perovskite solar cells and carbon-based

Herein, at first, green SnO2@ZnO nanocomposites were synthesized using Calotropis plant extract as an electron transfer material (ETM) to fabricate low-temperature-processed perovskite solar cells (PSCs). Then, the polyaniline (PANI) polymer was applied as an efficient additive to improve perovskite film quality. Under the effects of the small content of PANI additive, the quality of perovskite films is enhanced, which showed higher crystallinity in (110) crystal plane; also, the perovskite grains were found to be enlarged from 342 to 588 nm. The power conversion efficiency (PCE) of the prepared PSCs with SnO2@ZnO.PANI nanocomposites electron transfer layer (ETL) increased by 3.12%, compared with the PCE of SnO2@ZnO nanocomposites. The perovskite devices using SnO2@ZnO.PANI nanocomposites ETL have shown good stability during 480 h of tests. Furthermore, the optimal PSCs were fabricated by the mp-TiO2/SnO2@ZnO.PANI nanocomposites as ETL, which has a power conversion efficiency of 15.45%. We expect that these results will boost the development of low-temperature ETL, which is essential for the commercializing of high-performance, stable, and flexible perovskite solar cells.

Design of all-inorganic hole-transport-material-free CsPbI3/CsSnI3 heterojunction solar cells by device simulation

The hole transport material (HTM)-free perovskite solar cells (PSCs) have attracted widespread interest due to enhanced stability and lowered cost as compared to the sandwich-type PSCs with an organic hole conductor. For the absorber layer, CsPbI3 has become a competitive candidate for its good chemical-components stability, excellent optoelectronic properties and most proper bandgap among inorganic halide perovskites. However, the power conversion efficiency of CsPbI3-based HTM-free PSCs is still much inferior to that of conventional ones. In this work, an all-inorganic-perovskite-heterojunction CsPbI3/CsSnI3 is proposed as the absorber and the HTM-free CsPbI3/CsSnI3 PSCs are investigated systematically through numerical simulation by using SCAPS-1D. Compared with the HTM-free PSCs employing a single CsPbI3 absorbing layer, the HTM-free CsPbI3/CsSnI3 PSCs have the extended absorption range and enhanced performance. The best cell efficiency is increased from 15.60% to 19.99% and from 13.87% to 19.59% for the cell with a back-front Au electrode and a back-front C electrode, respectively. It reveals that for the HTM-free CsPbI3/CsSnI3 heterojunction cells, C is a good choice for back-front electrode as it can achieve desirable cell performance with improved stability and lowered fabrication cost. These results indicate that the proposed HTM-free CsPbI3/CsSnI3 heterojunction cells are promising for photovoltaic applications.

Preparation of low-cost perovskite solar cells with high-quality perovskite films in an ambient atmosphere

High-quality perovskite films are extremely crucial to obtain perovskite solar cells with excellent photovoltaic performance, especially for carbon-based hole transport materials (HTM)-free perovskite solar cells. In this work, a facile and low-cost double two-step method (DT-method) is developed to prepare uniform and pinhole-free CH3NH3PbI3 perovskite films in an ambient atmosphere by utilizing the dissolution-recrystallization of PbI2 in DMF. That is to spin-coat PbI2 and CH3NH3I solution sequentially onto pristine perovskite films prepared by the conventional two-step method. The solar cells fabricated by the DT-method show a dramatic performance improvement, including V oc, J sc, and fill factor reach 0.85 V, 15.56 mA cm−2, and 0.58 respectively, which increase power conversion efficiency from 3.93% to 7.58% compared with the conventional two-step method. The improvement in performance and stability of solar cells is mainly due to the higher coverage of perovskite films onto the underlying mesoporous TiO2 layer and a negligible amount of PbI2 residue, which can effectively reduce charge recombination and promote the rapid transfer of charge carriers. In summary, this work presents a process for preparing carbon-based HTM-free perovskite solar cells (PSCs) in a high-humidity atmospheric environment (60%–85%). This simple device structure and preparation condition can greatly reduce the production threshold and cost of PSCs.

Designing hole conductor free tin–lead halide based all-perovskite heterojunction solar cell by numerical simulation

The simple structure and processing, low fabrication cost and high stability of the hole transport material (HTM)-free perovskite solar cells (PSCs) have great importance nowadays. In this study, an efficient and novel HTM-free PSC structure where CH3NH3Pb(I1-xClx)3/FA0.75Cs0.25Pb0.5Sn0.5I3 (where FA is formamidinium) acts as a light harvester, WS2 acts as an electron transport material (ETM) and carbon acts as the back electrode is proposed and was investigated numerically with the SCAPS-1D simulation tool. Initially three device structures having bare CH3NH3Pb(I1-xClx)3, CH3NH3Pb(I1-xClx)3/CsSnI3 and CH3NH3Pb(I1-xClx)3/FA0.75Cs0.25Pb0.5Sn0.5I3 absorbing layers with ZnO as an ETM were studied, and it was observed that among them the power conversion efficiency (PCE) of the CH3NH3Pb(I1-xClx)3/FA0.75Cs0.25Pb0.5Sn0.5I3-based device was the greatest. Also various ETMs and solar cell layer parameters, such as absorber thickness, defect density and doping concentration, were varied to obtain their optimum values. The optimum performance of the device thus achieved is VOC = 0.82 V, JSC = 31.94 mA/cm2, a fill factor of 77.95% and PCE of 20.53% with carbon as the back contact and VOC = 0.84 V, JSC = 34.34 mA/cm2, a fill factor of 78.54% and PCE of 22.72% with gold as the back contact. These simulation results indicate that the proposed new HTM-free PSC is quite efficient for photovoltaic applications.

Numerical Modeling and Analysis of HTM-Free Heterojunction Solar Cell Using SCAPS-1D

In this research paper, a HTM-free perovskite solar cell (PSC) structure with Titanium (TiO2), methyl ammonium lead triiodide (CH3NH3PbI3) and platinum (pt) as electron transport material (ETM), photon harvester and metal back contact is proposed. Solar Cell Capacitance Simulator (SCAPS-1D) program was used to implement the model and simulation. Effect of parameters such as thickness of ETM, thickness of absorber, doping concentration of ETM & absorber and electron affinity (EA) of ETM were investigated systematically. From the obtained results, it was found that the parameters affect the performance of the solar cell. When the thickness of ETM was varied from 0.02 to 0.10 μm. The results show that photovoltaic parameters decrease with the thickness increase. When the thickness of the absorber was varied from 0.1 to 1.0 μm, the optimized value was found at thickness of 0.4 . When the doping concentration of absorber and EMT were varied from 1010–1017 cm-3 and from 1015–1020 cm-3, the highest values of PCEs were obtained at 1016 cm-3 and 1020 cm-3 for Absorber and ETM. Also when the EA was varied in the range of 3.7 eV to 4.5 eV, the optimized value was at 3.7 eV. Upon optimization of the above mentioned parameters, power conversion efficiency (PCE) was found to be 25.75 %, short circuit current density (Jsc) 23.25 mAcm-2, open circuit voltage (Voc) 1.24 V and fill factor (FF) 89.50 %. The optimized result shows an improvement of ~1.95 times in PCE, ~1.06 times in Jsc, ~1.44 times in Voc and ~1.28 times in FF as compared to the initial device with the following parameters, PCE=13.22 %, Jsc=21.96 mAcm−2, Voc=0.86 V and FF=69.94 %.

Hysteresis Analysis of Hole-Transport-Material-Free Monolithic Perovskite Solar Cells with Carbon Counter Electrode by Current Density-Voltage and Impedance Spectra Measurements.

Due to the tremendous increase in power conversion efficiency (PCE) of organic–inorganic perovskite solar cells (PSCs), this technology has attracted much attention. Despite being the fastest-growing photovoltaic technology to date, bottlenecks such as current density–voltage (J–V) hysteresis have significantly limited further development. Current density measurements performed with different sweep scan speeds exhibit hysteresis and the photovoltaic parameters extracted from the current density–voltage measurements for both scan directions become questionable. A current density–voltage measurement protocol needs to be established which can be used to achieve reproducible results and to compare devices made in different laboratories. In this work, we report a hysteresis analysis of a hole-transport-material-free (HTM-free) carbon-counter-electrode-based PSC conducted by current density–voltage and impedance spectra measurements. The effect of sweep scan direction and time delay was examined on the J–V characteristics of the device. The hysteresis was observed to be strongly sweep scan direction and time delay dependent and decreased as the delay increased. The J–V analysis conducted in the reverse sweep scan direction at a lower sweep time delay of 0.2 s revealed very large increases in the short circuit current density and the power conversion efficiency of 57.7% and 56.1%, respectively, compared with the values obtained during the forward scan under the same conditions. Impedance spectroscopy (IS) investigations were carried out and the effects of sweep scan speed, time delay, and frequency were analyzed. The hysteresis was observed to be strongly sweep scan direction, sweep time delay, and frequency dependent. The correlation between J–V and IS data is provided. The wealth of photovoltaic and impendence spectroscopic data reported in this work on the hysteresis study of the HTM-free PSC may help in establishing a current density–voltage measurement protocol, identifying components and interfaces causing the hysteresis, and modeling of PSCs, eventually benefiting device performance and long-term stability.

All-Inorganic Perovskite Solar Cells Using Treated Carbon Materials for Effective Charge Extraction

Perovskite solar cells (PSCs) have become the leader in the field of the third-generation solar cells due to their outstanding photovoltaic performance and low cost. However, the instability stemming from low tolerance to humidity and heat as well as residual solvents and ultraviolet illumination would be challenging for long-term stability. Recently, all inorganic perovskites, especially carbon-based hole-transporting material (HTM) CsPbBr3 perovskite, have attracted increasing attentions because of their enhanced moisture and thermal stability compared to hybrid counterparts.For the CsPbBr3 device, a challenging route to increase power conversion efficiency (PCE) is to take interfacial charge transfer into consideration and reduce interfacial energy-level differences to reduce space charge accumulation and enhance charge extraction. It is known that graphene-based derivatives are promising candidates for interfacial materials due to their excellent electronic properties. For example, graphene quantum dots (GQDs) between perovskite and TiO2 could significantly enhance the performance of PSCs due to dramatically enhanced electron extraction by the inserted GQDs; polyaniline/graphite composites were incorporated into carbon electrode to tailor work function and to improve hole-selectivity of back electrode for enhanced energy level alignment and interfacial hole extraction, leading to a remarkably reduced energy loss and charge recombination.Herein, we developed a strategy to use carbon dots (CDs) with tunable bandgaps and high absorption coefficients for electron extraction performance. The CDs were prepared by exfoliation method from oxidized graphite, and CDs in dimethylformamide solution were spin-coated onto FTO/c-TiO2/m-TiO2 substrate, then a multistep solution-processed method was used to prepare Cs-Pb-Br films with controllable CsPbBr3 phase. Specifically, CsBr/methanol solution (~15 mg mL-1) was spin-coated onto PbBr2 film and then annealed at 250 °C for 5 min, and the processes were repeated for 5 times. The obtained cesium lead bromide films were washed by 2-propanol. Finally, a carbon back-electrode with an average area of 0.09 cm2 was deposited onto the device. We fabricated all-inorganic PSCs with the FTO/c-TiO2/m-TiO2/CDs/CsPbBr3/carbon structure. Arising from the suppressed interfacial charge recombination, the optimal device yielded a PCE up to 10.67% under one sun illumination. These findings suggest that graphene-based derivatives can be used as interfacial modification materials toward high-performance carbon-based HTM-free PSCs.

9.05% HTM free perovskite solar cell with negligible hysteresis by introducing silver nanoparticles encapsulated with P4VP polymer

This study is a follow up to our previously published manuscript on “improved power conversion efficiency in Perovskite solar cell using silver nanoparticles modified photoanode”. Three more photoanodes were fabricated which are: Ag@P4VP NPs mixed with perovskite layer (S2), Ag@P4VP NPs simultaneously mixed both in TiO2 and perovskite films (S3) and P25 NP simultaneously mixed both in TiO2 and perovskite absorber (S4) and their performances were investigated systematically. The performance, especially the photocurrent, and open circuit voltage of PSCs made of Ag@P4VP NPs were significantly affected. The champion device is S3, which shows enhancement in power conversion efficiency (PCE) from 3.80 to 9.05%, short circuit current density (Jsc) from 11.04 to 15.87 mA cm−2, open circuit voltage (Voc) from 0.85 to 0.88 and fill factor (FF) from 0.41 to 0.65, which demonstrates ~ 2.38 times improvement in PCE over the control device (C). When Ag@P4VP NPs was mixed with TiO2, PCE of 5.69%, Jsc of 12.61 mA cm−2, Voc of 0.88 V and FF of 0.51 were achieved, which shows ~ 1.50 times improvement over the performance of the reference cell. Also, when Ag@P4VP NPs was mixed with the perovskite layer, PCE of 8.08%, Jsc of 14.18 mA cm−2, Voc of 0.89 V and FF of 0.64 were achieved, which shows ~ 2.13 times improvement over the performance of the pristine device. The addition of Ag@P4VP NPs enhanced exciton generation and dissociation, encouraging charge separation/transfer, as well as reducing quenching losses. For the hysteresis test, it was found that the devices with Ag@P4VP NPs have almost identical J–V curves with negligible hysteresis, which is attributed to the significant reduction of the trap density of the perovskite film when Ag@P4VP NPs is incorporated to fill the pores with high trapping rate. We however observed hysteretic behavior in devices C and S4, which makes it difficult to estimate the real PCE.

Electrochemical Impedance Spectroscopy Analysis of Hole Transporting Material Free Mesoporous and Planar Perovskite Solar Cells.

The future photovoltaic technologies based on perovskite materials are aimed to build low tech, truly economical, easily fabricated, broadly deployable, and trustworthy solar cells. Hole transport material (HTM) free perovskite solar cells (PSCs) are among the most likely architectures which hold a distinctive design and provide a simple way to produce large-area and cost-effective manufacture of PSCs. Notably, in the monolithic scheme of the HTM-free PSCs, all layers can be printed using highly reproducible and morphology-controlled methods, and this design has successfully been demonstrated for industrial-scale fabrication. In this review article, we comprehensively describe the recent advancements in the different types of mesoporous (nanostructured) and planar HTM-free PSCs. In addition, the effect of various nanostructures and mesoporous layers on their performance is discussed using the electrochemical impedance spectroscopy (EIS) technique. We bring together the different perspectives that researchers have developed to interpret and analyze the EIS data of the HTM-free PSCs. Their analysis using the EIS tool, the limitations of these studies, and the future work directions to overcome these limitations to enhance the performance of HTM-free PSCs are comprehensively considered.

Greatly enhanced power conversion efficiency of hole-transport-layer-free perovskite solar cell via coherent interfaces of perovskite and carbon layers

Abstract The interfacial contact between a perovskite and a carbon layer significantly affects the photovoltaic performance of a paintable and carbon-based hole transport material (HTM)-free perovskite solar cell (PSC). However, the detailed mechanism of the performance degradation, with regard to the carrier dynamics behavior at the perovskite/carbon interface, has not been elucidated yet. In this study, the improved interface of the perovskite/carbon was designed via a newly carbon electrode with nanosized carbon black and carbon fibers. Meanwhile, the modified Mott-Schottky analysis is conducted to study the carrier dynamics in the coherent and sparsely contacting interfaces, revealing that the unrestricted excitons in the nanoscale non-contact region of the coherent interface can be separated and then drove to be transported by the lateral built-in electric field. Furthermore, the HTM-free PSC via improved material design and fabrication by using a bilayer carbon electrode (coherent layer and conductive layer) results in an enhanced champion efficiency of 14.1%.

Electrical equivalent circuit (EEC) based impedance spectroscopy analysis of HTM free perovskite solar cells

Monolithic perovskite solar cells (mPSCs) are the multi-layered organic-inorganic hybrid cells that have been focused due to the affordable cost, ease of fabrication, and noteworthy power conversion efficiency (PCE). In this research, we have carried out a systematic study to understand the physical phenomenon inside successive layers of the mPSCs by using the impedance spectroscopy (IS) tool. The analysis has performed under the multiple applied potential to observe the changes in the complex plane (Nyquist) plot and their effect on the performance of different layers of the mPSCs. The IS analysis for each successive layer of the porous electrode has also conducted to distinguish their contribution to the Nyquist plot. The effect of the carbon layer and perovskite has been validated by performing the IS analysis in sequence after the deposition of each of these layers. The internal electrical processes at the interfaces of the layers of mPSC devices have been related to produce an electrical equivalent circuit (EEC) of an overall mPSC device. The data of the optimized mPSCs with power conversion efficiency over 13% has been used to perform the EEC analysis, where multi-cations perovskite film has been employed as a light absorber.

Design of hole-transport-material free CH3NH3PbI3/CsSnI3 all-perovskite heterojunction efficient solar cells by device simulation

The hole-transport-material (HTM) free perovskite solar cells (PSCs) have drawn great attentions due to the simple structure, low fabrication cost and long term stability. However, the photoelectric conversion efficiency (PCE) of the HTM-free PCSs are still low comparing with the traditional sandwich type PSCs. In this work, a new HTM-free PSC is proposed with CH3NH3PbI3/CsSnI3 all-perovskite heterojunction as light-harvester and carbon as back electrode through simulation using the wxAMPS tools. The results are analyzed and compared with the traditional HTM-free perovskite solar cells. It reveals that the narrow band gap CsSnI3 broadens the absorption spectrum to near-infrared region and the high hole mobility favors efficient hole transfer. The optimal performance is achieved as Voc = 1.08 eV, Jsc = 25.33 mA/cm2, FF = 79.27%, PCE = 21.64%. Comparing to the bare CH3NH3PbI3 absorbing layer, the device efficiency of CH3NH3PbI3/CsSnI3 heterojunction is improved from 18.29% to 21.64%. This indicates that the proposed HTM-free PSC is promising for future photovoltaic and optoelectronics applications.

Advanced hermetic encapsulation of perovskite solar cells: the route to commercialization

An advanced laser-assisted sealing method was developed and used to hermetically encapsulate HTM-free perovskite solar cells.

Enhanced energy level alignment and hole extraction of carbon electrode for air-stable hole-transporting material-free CsPbBr3 perovskite solar cells

Carbon-based hole-transporting material (HTM)-free CsPbBr3 perovskite solar cells (PSCs) provide new opportunities for promoting the commercial application of PSCs because of the low cost, simple preparation process and excellent stability under various extreme conditions. One of the remaining problems for inorganic CsPbBr3 PSCs is the low power conversion efficiency (PCE) due to the large energy level difference and inefficient hole extraction at CsPbBr3/carbon interface. Herein, polyaniline/graphite (PANi/G) composites are incorporated into carbon electrode to tailor work function and to improve hole-selectivity of back electrode for enhanced energy level alignment and interfacial hole extraction, leading to a remarkably reduced energy loss and charge recombination. The HTM-free CsPbBr3 PSC based on carbon-PANi/G electrode achieves a PCE of 8.87%, which is increased by 43.8% in comparison with 6.17% for the control device. Moreover, the unencapsulated device shows excellent long-term moisture tolerance with the initial PCE maintaining 93.5% even exposure to air atmosphere with 80% RH at 25 °C over 50 days. The successful improvement of energy level alignment and charge extraction in device by directly incorporating PANi/G composites into carbon electrode offers a promising strategy in developing low-cost and efficient HTM-free PSCs.