Dopant-free Hole Transport Layer Research Articles

Dibenzo[b,d]thiophene 5,5-dioxide-based dopant-free hole-transporting material with passivation effect in inverted perovskite solar cells

For the rocket development of organic-inorganic hybrid perovskite solar cells (OIH–PSCs), the research of low-cost, dopant-free hole-transporting materials (HTMs) with high performance and stability is still an urgent problem. In this work, we synthesize organic small molecule HTM with sulfone-containing benzodithiophene (BDTOxide) as the central unit, termed BDTOxide-MTP. The synthetic cost of DBTOxide-MTP in the lab is 238 CNY/g, which is just one-fifth of the cost of the PTAA (1200 CNY/g). BDTOxide-MTP exhibits the deep highest occupied molecular orbital energy level, high hole transport mobility, and excellent passivation effect. BDTOxide-MTP is introduced into inverted OIH-PSCs as a dopant-free hole transport layer, the champion efficiency of MAPbI3-xClx-based devices reaches 18.72 % with an excellent VOC of 1.13 V, while the efficiency of the control device based on PTAA is about 18.49 %. The device based on BDTOxide-MTP exhibits comparable stability to the one based on PTAA, which can maintain over 90 % of the original efficiency after 46 days in a nitrogen environment.

Dopant-Free Hole-Transporting Material Based on Poly(2,7-(9,9-bis(N,N-di-p-methoxylphenylamine)-4-phenyl))-fluorene for High-Performance Air-Processed Inverted Perovskite Solar Cells.

It is a great challenge to develop low-cost and dopant-free polymer hole-transporting materials (HTM) for PSCs, especially for efficient air-processed inverted (p-i-n) planar PSCs. A new homopolymer HTM, poly(2,7-(9,9-bis(N,N-di-p-methoxylphenyl amine)-4-phenyl))-fluorene (denoted as PFTPA), with appropriate photo-electrochemical, opto-electronic and thermal stability, was designed and synthesized in two steps to meet this challenge. By employing PFTPA as dopant-free hole-transport layer in air-processed inverted PSCs, a champion power conversion efficiency (PCE) of up to 16.82% (0.1 cm2) was achieved, much superior to that of commercial HTM PEDOT:PSS (13.8%) under the same conditions. Such a superiority is attributed to the well-aligned energy levels, improved morphology, and efficient hole-transporting, as well as hole-extraction characteristics at the perovskite/HTM interface. In particular, these PFTPA-based PSCs fabricated in the air atmosphere maintain a long-term stability of 91% under ambient air conditions for 1000 h. Finally, PFTPA as the dopant-free HTM was also fabricated the slot-die coated perovskite device through the same fabrication condition, and a maximum PCE of 13.84% was obtained. Our study demonstrated that the low-cost and facile homopolymer PFTPA as the dopant-free HTM are potential candidates for large-scale production perovskite solar cell.

Dopant-Free Polymer Hole Transport Materials for Highly Stable and Efficient CsPbI3 Perovskite Solar Cells.

All-inorganic perovskite CsPbI3 contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI3 readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI3 PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N2 for 3000h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.

High-Hole-Mobility Metal\u2013Organic Framework as Dopant-Free Hole Transport Layer for Perovskite Solar Cells

A dopant-free hole transport layer with high mobility and a low-temperature process is desired for optoelectronic devices. Here, we study a metal–organic framework material with high hole mobility and strong hole extraction capability as an ideal hole transport layer for perovskite solar cells. By utilizing lifting-up method, the thickness controllable floating film of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 at the gas–liquid interface is transferred onto ITO-coated glass substrate. The Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 film demonstrates high compactness and uniformity. The root-mean-square roughness of the film is 5.5 nm. The ultraviolet photoelectron spectroscopy and the steady-state photoluminescence spectra exhibit the Ni3(HITP)2 film can effectively transfer holes from perovskite film to anode. The perovskite solar cells based on Ni3(HITP)2 as a dopant-free hole transport layer achieve a champion power conversion efficiency of 10.3%. This work broadens the application of metal–organic frameworks in the field of perovskite solar cells.Graphical

Enhancing the efficiency and stability of perovskite solar cells based on moisture-resistant dopant free hole transport materials by using a 2D-BA2PbI4 interfacial layer.

In this work, the photovoltaic performance and stability of perovskite solar cells (PSCs) based on a dopant-free hole transport layer (HTL) are efficiently improved by inserting a two-dimensional (2D) interfacial layer. The benzyl ammonium lead iodide (BA2PbI4) 2D perovskite is used as an interfacial layer between the 3D CH3NH3PbI3 perovskite and two moisture-resistant dopant-free HTLs including poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) and poly(3-hexylthiophene) (P3HT). TQ1 with a facile synthesis procedure has a higher moisture resistivity compared to P3HT which can improve the stability of PSCs. The 2D BA2PbI4 perovskite with a less-volatile bulkier organic cation efficiently passivates the defects at the perovskite/HTL interface, leading to 11.95% and 15.04% efficiency for the modified TQ1 and P3HT based cells, respectively. For a better understanding, the structural, optical, and electrical properties of PSCs comprising P3HT and TQ1 HTLs with and without interface modification are studied. The interface modified PSCs show slower open-circuit voltage decay and longer carrier lifetimes compared to unmodified cells. In addition, impedance spectroscopy reveals lower charge transport resistance and higher recombination resistance for the modified devices, which could be associated with the modification of the interface between the 3D CH3NH3PbI3 perovskite and HTL caused by the 2D interfacial layer. Also after aging under ambient conditions for about 800 hours, the modified PCSs retain more than 80% of their initial PCEs. These results give us the hope of achieving simpler, cheaper, and more stable PSCs with dopant-free HTLs through 2D interfacial layers, which have great potential for commercialization.

Design of Dopant and Lead-Free Novel Perovskite Solar Cell for 16.85% Efficiency.

Halide based perovskite offers numerous advantages such as high-efficiency, low-cost, and simple fabrication for flexible solar cells. However, long-term stability as well as environmentally green lead-free applications are the real challenges for their commercialization. Generally, the best reported perovskite solar cells are composed of toxic lead (Pb) and unstable polymer as the absorber and electron/hole-transport layer, respectively. Therefore, in this study, we proposed and simulated the photovoltaic responses of lead-free absorber such as cesium titanium (IV) bromide, Cs2TiBr6 with dopant free electron phenyl-C61-butyric acid methyl ester (PCBM), and dopant free hole transport layer N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) for the Ag/BCP/PCBM/Cs2TiBr6/NPB/ITO based perovskite solar cell. After comprehensive optimization of each layer through vigorous simulations with the help of software SCAPS 1D, it is observed that the proposed solar cell can yield maximum power-conversion efficiency up to 16.85%. This efficiency is slightly better than the previously reported power-conversion efficiency of a similar type of perovskite solar cell. We believe that the outcome of this study will not only improve our knowledge, but also triggers further investigation for the dopant and lead-free perovskite solar cell.

Improving the Fill Factor of Perovskite Solar Cells by Employing an Amine-tethered Diketopyrrolopyrrole-Based Polymer as the Dopant-free Hole Transport Layer

Although rapid progress has been witnessed recently in regular perovskite solar cells (PSCs), one of the bottlenecks to delay their industrialization is the complicated and poor reproducible doping process of the widely used hole-transporting material (HTM) spiro-OMeTAD. To address this issue, herein, an unreported polymer, P25NH, has been synthesized and adopted as a dopant-free hole transport layer (HTL) in PSCs. Compared with the commonly used HTM poly(3-hexylthiophene), P25NH shows better aggregation property, enhanced ability of passivation to the perovskite surface, and higher mobility, which could greatly reduce series resistance and improve the fill factor. The PSCs with P25NH (1.6 mg/mL) as HTLs exhibited a decent power conversion efficiency (PCE) of 18.1% with a high fill factor of 81.9% (at 6 mg/mL, the fill factor is 83.2%). This work provides an alternative polymer for scalable dopant-free HTMs and a simple device structure for achieving high PCE.

A crosslinked polymer as dopant-free hole-transport material for efficient n-i-p type perovskite solar cells

A new crosslinked polymer, called P65, with appropriate photo-electrochemical, opto-electronic, and thermal properties, has been designed and synthesized as an efficient, dopant-free, hole-transport material (HTM) for n-i-p type planar perovskite solar cells (PSCs). P65 is obtained from a low-cost and easily synthesized spiro[fluorene-9,9′-xanthene]-3′,6′-diol (SFX-OH)-based monomer X65 through a free-radical polymerization reaction. The combination of a three-dimensional (3D) SFX core unit, hole-transport methoxydiphenylamine group, and crosslinked polyvinyl network provides P65 with good solubility and excellent film-forming properties. By employing P65 as a dopant-free hole-transport layer in conventional n-i-p type PSCs, a power conversion efficiency (PCE) of up to 17.7% is achieved. To the best of our knowledge, this is the first time a 3D, crosslinked, polymeric dopant-free HTM has been reported for use in conventional n-i-p type PSCs. This study provides a new strategy for the future development of a 3D crosslinked polymeric dopant-free HTM with a simple synthetic route and low-cost for commercial, large-scale applications in future PSCs.

4-Tert-butylpyridine-assisted low-cost and soluble copper phthalocyanine as dopant-free hole transport layer for efficient Pb- and Sn-based perovskite solar cells

The preparation of suitable hole transport material (HTM) is critical to the performance and stability of perovskite solar cells (PSCs) with low-cost. Herein, a mass producible and soluble copper phthalocyanine decorated with butoxy donor groups (CuPc-OBu) was designed as HTM and prepared by a facile two-step synthetic route. To generate high quality HTM film, 4-tert-butylpyridine (tBP) was doped into CuPc-OBu to prepare the film and then removed by annealing. Such a tBP-assisted strategy resulted in the best efficiency of the PSCs with lead trihalide perovskite up to 19.0% (small-area of 0.1 cm2) and 10.1% (the active area of 8.0 cm2 for the module device). And the best efficiency of the tin-based PSCs with CuPc-OBu reached to 6.9%. More importantly, the device with CuPc-OBu as HTM revealed the remarkably enhanced stability. This work provides a new strategy to improve the film-quality of free-doping HTMs and enhance the efficiency and stability of Pb- and Sn-based PSCs with low-cost.

Study on the stability of the mixed (MAPbI3 and MAPbBr3) perovskite solar cells using dopant-free HTL

Abstract This study sheds a light on the instability and degradation factors occurring within the dopant-free hole transport layer (HTL) based perovskite solar cells with aging time. To prepare the perovskite solar cells (PSCs), a layer-by-layer deposition method was adopted. The PSCs were prepared in the conventional n-i-p structure using the mixed perovskite (MAPbI3 and MAPbBr3) solution. FA-CN based dopant-free HTL was deposited on the top of the perovskite layer using the spin coating procedure. The fresh and aged (for 45, 90 and 180 days) PSCs were studied by using current-voltage (I–V) characterization technique and impedance spectroscopy (IS). The average power conversion efficiency (PCE) of the freshly prepared PSCs was ~15.98%. With the aging, the hysteresis in the I–V characteristics was increased and a noticeable rise in the deep traps has been noted. IS spectra demonstrates that charge transfer resistance of the samples was reduced with the passage of time, which indicates that the compact-TiO2 layer (blocking layer) might be degraded and the electrical properties of the FTO/TiO2/perovskite interfaces have been effected. Furthermore, the recombination resistance of the samples has also been decreased significantly during the aging process. Based on the experimental results, fundamental features that account for the instability in the perovskite solar cells have been discussed.

Solution-Processable Cu(II) Phthalocyanine Derivative as Dopant-Free Hole Transport Layer for Efficient and Low-Cost Rutile TiO2 Array-Based Perovskite Solar Cells

The full-scale commercialization of the organometallic perovskite solar cells, as one of the most high-efficiency photovoltaic technology, needs to lower the cost and improve the long-term stability by further optimizing the device architecture and component materials. In this context, a solution-processable tert-butyl-substituted Cu(II) phthalocyanine (CuPc(tBu)4) is employed as dopant-free hole transport layer to fabricate a low-cost and high-efficiency perovskite solar cell with a low-temperature processed rutile TiO2 array as electron transport layer and a mixed-ion perovskite (Cs0.05(FA0.83MA0.17)0.95Pb(I0.9Br0.1)3) as light absorber. It is found that the optimized rutile TiO2 array film-based solar cell with the dopant-free Cu(II) phthalocyanine hole transport layer achieves a power conversion efficiency of 13.7% with less hysteresis, which can be further enhanced to 14.8% after introducing Al2O3 buffer layer between the Cu(II) phthalocyanine hole transport layer and the perovskite layer due to the ...

Eliminating Light-Soaking Instability in Planar Heterojunction Perovskite Solar Cells by Interfacial Modifications

Stability remains as a challenge of perovskite solar cells although encouraging progress has been made toward their maximum achievable power conversion efficiency in recent years. Light-soaking issue, where the device performance improves upon continuous light illumination and reduces upon storage in dark, is widely observed and marked as the early-stage instability during device operation. In this work, we have employed conjugated polymer PCDTBT as the dopant-free hole-transport layer to fabricate devices without hysteresis but with reversible light-soaking instability. The introduction of n-type molecules, either organic molecule PDI2 or fullerene derivative PC61BM, as the interfacial layer between TiO2 and perovskite layers can effectively reduce or eliminate this instability owing to the efficient charge transport and defect passivation at the electron-transport layer interface, accompanied with an efficiency of 15.7 and 17.7%, respectively. We conclude that the light-soaking instability of these perovskite solar cells is mainly originated from the charge accumulation at the TiO2/perovskite interface and can be eliminated once the interfacial charge can be suppressed by interfacial modifications to improve charge transport at the interface.