Triiodide Perovskite Solar Cells Research Articles

Optimizing band gap, electron affinity, & carrier mobility for improved performance of formamidinium lead tri-iodide perovskite solar cells

Perovskite solar cells (PSC) offer the advantage of tunable nature, allowing for the adjustment of cell design parameters to enhance performance. This study focuses on the crucial role of tuning band gap, electron affinity, carrier mobility, thickness, and doping in improving the performance of Formamidinium lead tri-iodide (FAPbI3) PSCs. The PSC structure incorporates two carbon allotropes, PCBM and C60, as electron transport layers (ETLs), in conjunction with copper-based materials (CuAlO2, CuI, Cu2O) as hole transport layers (HTLs) to leverage their exceptional thermal and electrical conductivity. Using SCAPS-1D, six distinct PSC structures with various combinations of ETLs and HTLs are analyzed. The investigations employ continuity and Poisson equations to explore the impact of the design parameters on PSC performance. Additionally, a comprehensive assessment is conducted to evaluate energy band alignment, band offset, electric field distribution, recombination and defects. Through meticulous investigations, the study identifies the optimal combination of Cu-HTL and C-ETL that yields exceptional PSC performance. Specifically, employing CuAlO2 as the HTL and PCBM as the ETL achieves remarkable results, with a high PCE of 26.49 %, a Voc of 1.25 V, a Jsc of 23.51 mA/cm2, and an FF of 89.49 %.

Inhibition of defect-induced α-to-δ phase transition for efficient and stable formamidinium perovskite solar cells

Defects passivation is widely devoted to improving the performance of formamidinium lead triiodide perovskite solar cells; however, the effect of various defects on the α-phase stability is still unclear. Here, using density functional theory, we first reveal the degradation pathway of the formamidinium lead triiodide perovskite from α to δ phase and investigate the effect of various defects on the energy barrier of phase transition. The simulation results predict that iodine vacancies are most likely to trigger the degradation, since they obviously reduce the energy barrier of α-to-δ phase transition and have the lowest formation energies at the perovskite surface. A water-insoluble lead oxalate compact layer is introduced on the perovskite surface to largely suppress the α-phase collapse through hindering the iodine migration and volatilization. Furthermore, this strategy largely reduces the interfacial nonradiative recombination and boosts the efficiency of the solar cells to 25.39% (certified 24.92%). Unpackaged device can maintain 92% of its initial efficiency after operation at maximum power point under simulated air mass 1.5 G irradiation for 550 h.

Systematic investigation of the impact of kesterite and zinc based charge transport layers on the device performance and optoelectronic properties of ecofriendly tin (Sn) based perovskite solar cells

Methylammonium tin triiodide (MASnI3) perovskite solar cells (PSC) have gained a lot of interest due to their edge over conventional Pb-based PSC in terms of less-toxic nature, wider optical absorption range and smaller bandgap. In this work, 24 novel n-i-p heterostructures of MASnI3 PSC have been analyzed in detail with various zinc-based electron transport layers (ETL) and kesterite-based hole transport layers (HTL). The proposed device architecture (FTO/ETL/CH3NH3SnI3/HTL/Back contact) performance was first enhanced by optimizing the thickness and then by the doping concentration of each layer via SCAPS-1D simulator under AM 1.5G illumination. The energy band alignment of the different charge transport layers (CTL) with MASnI3 was analyzed in detail to understand its working principle. Moreover, the effects of optical absorption, band offsets, electric field, defect density, interface defects, temperature, rear reflective coating, and electrodes are monitored to characterize the performance of each cell structure. Among all the proposed structures, ZnO/MASnI3/CNTS based perovskite solar cell performed outstandingly well with Jsc of 29.44 mA cm−2, Voc of 1.12 V, FF of 88.82 %, and PCE of 29.24 %. These simulations provided important insights into the mechanism of carrier transport and the factors affecting the performance of solar cells. The results in this paper will help the research community in fabricating highly efficient eco-friendly solar cells.

Influence of the Alkyl Chain Length of (Pentafluorophenylalkyl) Ammonium Salts on Inverted Perovskite Solar Cell Performance.

We study the effect of (2,3,4,5,6-pentafluorophenyl)alkylamine additives with differing alkyl chain lengths (methyl, ethyl, and n-propyl) on the performance of methylammonium lead triiodide (MAPbI3) perovskite solar cells. The results show that the length of the alkyl chain between the 2,3,4,5,6-pentafluorophenyl group and ammonium moiety has a critical effect on the perovskite film structure and subsequent device performance. The 2,3,4,5,6-pentafluorophenyl ammonium additive with the shortest linking group (a methylene unit), namely (2,3,4,5,6-pentafluorophenyl)methylammonium iodide, was found to be distributed throughout the bulk of the perovskite film with a 2D phase only being observable at high concentrations (>30 mol%). In contrast, the additives with ethyl and n-propyl linking groups phase-separate during solution processing and are found to concentrate at the surface of the perovskite film. Photoluminescence measurements showed that the fluorinated additives passivated the surface defects on the perovskite grains. Of the three additives, inverted devices containing 0.32 mol% of the 2,3,4,5,6-pentafluorophenyl ammonium additive with the methylene linking group achieved a maximum power conversion efficiency of 22.0%, with the device efficiency decreasing with increasing additive concentration. In contrast, the devices composed of the additive with the longest alkyl linker, 3-(2,3,4,5,6-pentafluorophenyl)propylammonium iodide, had the poorest performance, with PCEs less than that of the neat MAPbI3 control and decreasing with increasing additive concentration.

Iodide and charge migration at defective surfaces of methylammonium lead triiodide perovskites: The role of hydrogen bonding

Methylammonium lead triiodide perovskite (CH3NH3PbI3) solar cells have exhibited impressive potential in photovoltaic applications, encouraging further work to improve operating stability. Ionic migration has been proposed to be a possible cause of the current–voltage hysteresis which is responsible for the instability of the CH3NH3PbI3 solar cells. Motivated by the variation of the surface geometries of the CH3NH3PbI3 material when going from the pristine to defective surfaces with the iodine vacancies, we adopt the density functional theory method to study the iodide migration along different paths at the defective surfaces followed by employing the time-dependent density functional theory method to calculate the light-induced electronic states along the paths. We find that the iodide movement is largely tuned by the reorientation and rotation of the organic cations with the disruption and formation of the hydrogen bonding during the iodide migration. Besides, the migration of the light-induced charge carriers varies along the paths with different orientations of the organic cations. We attribute the complicated dynamics of the mobile iodide ions and the associated trap states to the hydrogen bonding at the surfaces, providing crucial guidance for improving the stability and charge carrier lifetime in the CH3NH3PbI3 and other metal halide perovskites.

Efficient and stable pure α-phase FAPbI3 perovskite solar cells with a dual engineering strategy: Additive and dimensional engineering approaches

Formamidinium lead triiodide (FAPbI3) perovskite solar cells (PSCs) with a certified 25.5% power conversion efficiency (PCE) are the most promising devices for next-generation of solar cells. Here, we focus on boosting the performance and stability of these types of PSCs through a two-step engineering method, first additive engineering based on propionic acid for 3D FAPbI3 PSCs. Second, post-treatment of 3D devices with a 2-(4-fluorophenyl)ethyl ammonium iodide (FPEAI) solution doped with nitrosonium tetrafluoroborate (NOBF4). This two-step approach improves carriers' lifetime and charges separation at 3D/2D perovskite/hole transport layer (HTL), tiding with improvements in photovoltaic properties of corresponding PSCs. Besides, NOBF4 p-type dopant increases hole mobility at the interface of the 3D/2D hybrid perovskite/HTL, thus providing a road towards more boosting efficiency and stability of PSCs through dimensional engineering. Leading to improved properties of the perovskite, the modified 3D/2D PSCs achieve a PCE of up to 23.18% with long-term shelf, thermal and operational stability.

Organic cation – polystyrene sulfonate polyelectrolytes as hole transporting interfacial layers in perovskite solar cells

Interfacial layers are important tools that can be used to control the band structure and performance of perovskite solar cells, however, relatively few p-type materials are known compared to n-type interfacial materials. In this work, we demonstrate that anionic polystyrene sulfonate (PSS) polyelectrolytes, with organic cations as counter ions, are able to function as p-type interfacial layers in methylammonium lead triiodide (MAPbI3) perovskite solar cells. These polyelectrolytes show interfacial dipole formation resulting in a significant increase in the work function of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and decrease in the Fermi energy of the CH3NH3PbI3 layer (band bending) as evident from x-ray photoelectron spectra (XPS) and ultraviolet photoelectron spectra (UPS) analysis. These effects result in superior electron blocking and hole extracting characteristics at the anode. We show that open circuit voltage, power conversion efficiency and other device parameters can be increased compared to the devices without interfacial layers using these convenient polyelectrolytes.

Imidazolium-based ionic liquid for stable and highly efficient black-phase formamidinium-based perovskite solar cell

The stable black α-phase is the key to attaining high-efficiency formamidinium lead triiodide (FAPbI3) perovskite solar cells (PSCs). There have been some reports using different sizes of ions to stabilize α-phase FAPbI3; unfortunately, they often affect the bandgap, stability and carrier dynamics, in addition to increasing the number of carrier trap sites. Herein, we present 1-allyl-3-methylimidazolium-chloride (AMICl) ionic liquid to stabilize the α-phase of pure FAPbI3 perovskite without encountering the above adversities. It is found that the thermodynamic temperature of α-FAPbI3 is significantly reduced from 150 °C to 145 °C by using AMICl, and the absorption edge of FAPbI3 remains at 850 nm. The efficiency of a FAPbI3 device with AMICl is increased from 18.47% for the control device to 20.76%, one of the highest values among pure FAPbI3 solar cells. The high efficiency is attributed to the low trap density, long carrier lifetime and suppressed carrier recombination, thanks to the large grain size and good crystallinity of FAPbI3 generated by the formation of intermediate products from PbI2 and AMICl, demonstrating by density functional theory (DFT) calculation. Meanwhile, FAPbI3 solar cells with AMICl exhibit the excellent environmental stability. The bare device without any encapsulation maintains about 87% of its initial value after being exposed to ambient for 24 days, significantly improved over the control device, which retains about 53% of its initial efficiency under the same conditions.

Mixing of Azetidinium in Formamidinium Tin Triiodide Perovskite Solar Cells for Enhanced Photovoltaic Performance and High Stability in Air.

Overcoming the issue of the stability of tin-based perovskites is a major challenge for the commercial development of lead-free perovskite solar cells. To attack this problem, a new organic cation, azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI3 ) to form the mixed-cation perovskite AZx FA1-x SnI3 . As AZ has a similar size to FA but a larger dipole moment, hybrid AZx FA1-x SnI3 films exhibit variation in optical and electronic properties on increasing the proportion of AZ. Trifluoromethylbenzene (CF3 C6 H5 ) serves as antisolvent to fabricate smooth and uniform perovskite films for the devices with an inverted planar heterojunction structure. The device performance is optimized to produce the greatest efficiency at x=0.15 (AZ15), for which a power conversion efficiency of 9.6 % is obtained when the unencapsulated AZ15 device is stored in air for 100 h. Moreover, the device retains 90 % of its initial efficiency for over 15 days. The significant performance and stability of this device reveal that the concept of mixed cations is a promising approach to stabilize tin-based perovskite solar cells for future commercialization.

Stabilization of formamidinium lead triiodide α-phase with isopropylammonium chloride for perovskite solar cells

Formamidinium lead triiodide (FAPbI3) perovskite solar cells (PSCs) are mainly fabricated by sequentially coating lead iodide and formamidinium iodide, or by coating a solution in which all components are dissolved in one solvent (one-pot process). The PSCs produced by both processes exhibited similar efficiencies; however, their long-term stabilities were notably different. We concluded that the major reason for this behaviour is the stabilization of the α-FAPbI3 phase by isopropylammonium cations produced by the chemical reaction between isopropyl alcohol, used as solvent, and methylammonium chloride, added during the process. On this basis, we fabricated PSCs by adding isopropylammonium chloride to the perovskite precursor solution for the one-pot process and achieved a certified power conversion efficiency of 23.9%. Long-term operational current density–voltage measurements (one sweep every 84 min under 1-Sun irradiation in nitrogen atmosphere) showed that the as-fabricated device with an initial efficiency of approximately 20% recorded an efficiency of about 23% after 1,000 h that gradually degraded to about 22% after an additional 1,000 h. The operational stability of formamidinium lead triiodide solar cells varies with the fabrication method of the perovskite layer. Now Park et al. find that isopropylammonium stabilizes the perovskite structure and leads to solar cells with 2,000-h stability under constant illumination.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Elucidating the Role of Ion Migration and Band Bending in Perovskite Solar Cell Function at Grain Boundaries via Multimodal Nanoscale Mapping

AbstractAlthough hybrid organic–inorganic halide perovskite solar cells have achieved extraordinary improvements over the past few years, questions remain about the role of grain boundaries. This article reports on the nanoscale point‐by‐point current–voltage mapping of photovoltaic characteristics in inverted methylammonium lead triiodide perovskite solar cells. These measurements reveal an increased open‐circuit voltage and shunt resistance, along with a suppressed short‐circuit photocurrent at grain boundaries and nearby regions. Support from nanoscale ionic strain and surface potential mapping suggests that local ion accumulation and downward band bending can facilitate charge separation, but hinder charge collection at grain boundaries.

Fast and feasible fabrication of zinc- and lithium-doped cobalt oxide layers as an emerging hole injection candidate for perovskite solar cells

Metal oxide-based hole injection layers inherent for stable third-generation methylammonium lead tri-iodide (CH3NH3PbI3) perovskite solar cells. Particularly for inverted types, their structural and optoelectronic properties determine the limit of the power conversion efficiencies. This work demonstrates a novel cobalt oxide-based hole injection layer (HIL) and metal doping effect on its performance. Using a fast and feasible solution-based route and employing Zn and Li as dopant sources, a systematic study is presented through photovoltaic performances. Structural and morphological properties and the effect of doping on the hole injection layers were examined through surface roughness, electrical and hole conductivity, bandgap, and crystalline structure analysis. In ambient air, glove-box free fabrication with a configuration of ITO/CoOx:ZnLi+/CH3NH3PbI3/PCBM/BCP/Ag boosted the efficiency up to 11.64 % from 3.99 % for pristine cobalt oxide employed devices. By employing optimum Zn and Li co-doping, open-circuit voltage, short-circuit current, fill factor of the pristine CoOx employed solar cell devices were changed from 882 to 925 mV, 8.6 to 19.7 mA/cm2 and 52.6 to 63.9, respectively. The enhancement of the photovoltaic performances linked to boosted hole mobility and electrical conductivity values for pristine and doped CoOx layers, from 0.55 × 10-6 cm2/Vs to 255 × 10-6 cm2/Vs and from 0.610 to 2.048 µS/cm, respectively. This report reveals the promising hole extraction capability of Zn and Li co-doped cobalt oxide layers for inverted CH3NH3PbI3-based perovskite solar cells.

Use of Sodium Diethyldithiocarbamate to Enhance the Open‐Circuit Voltage of CH3NH3PbI3 Perovskite Solar Cells

The incorporation of additives to modulate the properties of metal halide perovskite thin films has become a successful approach in improving the power conversion efficiency of perovskite‐based solar cells. Herein, the beneficial use of sodium diethyldithiocarbamate (NaDEDTC) as processing agent in improving the open‐circuit voltage of methylammonium lead triiodide perovskite solar cells is reported. DEDTC reduces the rate of perovskite crystallization. Absorption and emission spectra show that the optical bandgap of the perovskite films remain essentially unchanged and X‐ray diffraction reveals the formation of preferentially oriented crystallites independent of the use of DEDTC. The use of DEDTC, however, results in a decrease in nonradiative decay as inferred from a two order of magnitude increase in electroluminescence efficiency, explaining the increased open‐circuit voltage. Fourier‐transform infrared spectroscopy, nuclear magnetic resonance, and X‐ray photoelectron spectroscopy show that the DEDTC ligand is not present after the film processing. Therefore, DEDTC modulates film formation but is not incorporated in the perovskite or present as a surface ligand. Sodium ions, on the contrary, are incorporated in the perovskite layer.

Sustainable solvent selection for the manufacture of methylammonium lead triiodide (MAPbI3) perovskite solar cells

An approach for screening solvent systems for PSCs to substitute REACH restricted DMF with no loss in device performance.

Conversion efficiency enhancement of methylammonium lead triiodide perovskite solar cells converted from thermally deposited lead iodide via thin methylammonium iodide interlayer

The thermally deposited thin methylammonium iodide (MAI) interlayer worked as protection layer of poly (3, 4-ethylenedioxythiophene) poly (styrene sulfonate) (PEDOT:PSS) in the thermal deposition of lead iodide (PbI 2 ). And the thin MAI interlayer could be the MAI supplemental layer during converting the thermally deposited PbI 2 into perovskite. The performances of perovskite solar cells (SCs) converted from thermally deposited PbI 2 were remarkably enhanced by using the thin MAI interlayer on PEDOT:PSS. The short-circuit current density (J SC ), fill factor (FF%), and conversion efficiency (η%) of perovskite SCs converted from thermally deposited PbI 2 increased with the initial increase in thickness of the thin MAI interlayer and then reduced when the thickness of thin MAI interlayer exceeded 2.2 nm. Perovskite SCs converted from thermally deposited PbI 2 with a 2.2 nm-thick thin MAI interlayer obtained the largest J SC , FF%, and η% at 19.44 mA/cm 2 , 74% and 12.75%, respectively, in our study. And the largest J SC was more than twice larger than that of perovskite SCs converted from thermally deposited PbI 2 without thin MAI interlayer. Although the perovskite SCs converted from thermally deposited PbI 2 without thin MAI interlayer has η% much less than that of perovskite SCs converted from spin-coated PbI 2 . The perovskite SCs converted from thermally deposited PbI 2 with 2.2 nm-thick thin MAI interlayer had an η% of 12.75%, which was larger than that of perovskite SCs converted from spin-coated PbI 2 at 10.57%. • The thermally deposited thin MAI interlayer is a supplement of MAI for converting thermally deposited PbI 2 to perovskite. • The thermally deposited thin MAI interlayer is also a protection layer of PEDOT:PSS during the thermal deposition of PbI 2 . • The thin MAI interlayer leads great improvements on properties and performances of perovskite SCs.

Thermal Stability and Performance Enhancement of Perovskite Solar Cells Through Oxalic Acid-Induced Perovskite Formation

Achieving long-term stability along with high power conversion efficiency (PCE) is the biggest obstacle for the pursuit of organic–inorganic perovskite solar cells (PSCs) toward commercialization. Herein, we demonstrate additive assisted perovskite crystal growth as an effective strategy to improve both power conversion efficiency and thermal stability of methylammonium lead triiodide (MAPbI3) perovskite solar cells. For this, oxalic acid (OA) with two bifacial carboxylic acid groups was employed as an additive into the perovskite precursor solution, which facilitated modulating the crystallization process leading to increase in grain size, reduced grain boundaries and trap states. Subsequently, devices fabricated with the OA additive showed a power conversion efficiency of 17.12%, compared to the control device with 14.06%. Furthermore, enhanced thermal stability was achieved for the OA-modified PSCs compared to that of the pristine device. The device without the OA additive retained 14% of the initial PCE after only 9 h of heat treatment at 100 °C, whereas for the same condition, the OA-modified device retained 90% after 9 h and even 70% after 19 h. These observations suggest that OA-assisted morphological improvement of perovskite can offer an efficient approach to further improve the performance as well as stability of the PSCs.

Highly stable inverted methylammonium lead tri-iodide perovskite solar cells achieved by surface re-crystallization

A long-term operational stability over 1000 hours in the inverted type perovskite solar cells based on the MAPbI3 layer is demonstrated under ionic defect-free conditions.

Synergistic engineering of hole transport materials in perovskite solar cells

AbstractIn this work, methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cells with efficiencies higher than 18% were achieved using a new nanocomposite hole transport layer (HTL) by doping poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with a mixed dopant of polyaniline (PANI) and graphene oxide (GO). A synergistic engineering between GO, PANI, and PEDOT:PSS was accomplished to introduce additional energy levels between perovskite and PEDOT:PSS and increase the conductivity of PEDOT:PSS. Kelvin probe force microscope results confirmed that adding GO to PEDOT:PSS/PANI composite significantly reduced the average surface potential. This increased the open circuit voltage (Voc) to 1.05 V for the GO/PEDOT:PSS/PANI nanocomposite perovskite solar cells from the pristine PEDOT:PSS (Voc = 0.95 V) and PEDOT:PSS/PANI (Voc = 0.99 V). In addition, adding PANI to the HTLs substantially enhanced short circuit current density (Jsc). This was supported by the current sensing‐atomic force microscopy (CS‐AFM) and conductivity measurements. The PANI doped films showed superior electrical conductivity compared with those without PANI as indicated by CS‐AFM results. PANI can fill the gaps between the microflakes of GO and give rise to more compact hole transport material (HTM) layer. This led to a higher Jsc after doping with PANI, which was consistent with the incident photon‐to‐current efficiency and electrochemical impedance spectroscopy results. The results of X‐ray diffraction (XRD) and AFM indicated the GO/PANI doped HTMs significantly improved the crystallinity, topography, and crystal size of the perovskite film grown on their surface. A higher efficiency of 18.12% for p‐i‐n perovskite solar cells has been obtained by adding the mixed dopant of GO, PANI, and PEDOT:PSS, demonstrating better stability than the pristine PEDOT:PSS cell.image

Efficient Anti-solvent-free Spin-Coated and Printed Sn-Perovskite Solar Cells with Crystal-Based Precursor Solutions

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.