Characterization of F4TCNQ as a dopant in spiro-OMeTAD thin films by electron paramagnetic resonance spectroscopy.

Facile route of heterostructure CeO2–CuO nanocomposite as an efficient electron transport material for perovskite solar cells

Perovskite solar cells (PSCs) have recently received much attention in photovoltaics research due to their excellent performance. The PSCs have attained 25.2% power conversion efficiency (PCE) and more developments have been carried out to improve their PCE and functional stability. The PCE and stability of PSCs are controlled by each functional layer including the active layer, electron transporting layer (ETL), and hole transporting layer ( HTL). The ETL and HTL are important components in PSCs owing to their nature of effective charge collection. The hole-transporting materials (HTMs) in PSCs are categorized as organic, inorganic, and polymer-based hole transporting layers. Mainly, we are going to discuss numerous inorganic HTMs which possess high chemical stability as well as cost-effective material. Our aim is to provide detailed information of the design and fabrication details of novel HTMs to improve the PSC’s performance based on the recently reported HTMs. PSCs rely heavily on HTMs to improve the PCE and stability of the device. The number of HTMs such as organic, polymer, carbon, and inorganic materials has increased significantly in recent years. Among them, the all-inorganic HTMs are receiving great attention as they have a higher PCE and are more stable.

Inorganic p-type semiconductors and carbon materials based hole transport materials for perovskite solar cells

CuI and CuSCN as Hole Transport Materials for Perovskite Solar Cells Vinod E. Madhavan1*, Ahmer Ali Bozdar Baloch1, Afsal Manekkathodi1, Dhanasekaran Thirunvukkaarasu1, I. Zimmermann2, C. Roldán- Carmona2, G. Grancini2, M. Buffiere1, Mohammad Khaja Nazeeruddin2, A. Belaidi1 and Nouar Tabet1 1 Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, P. O. Box 5825, Doha, Qatar 2 Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, CH-1951 Sion, Switzerland *vmadhavan@qf.org.qa. ABSTRACT: Perovskite based solar cell is an important area of research for solar energy harvesting and for green energy revolution. The materials used for a thin film solar cell are considerably less with respect to the prevailing silicon based solar cells. There is an interest in copper based inorganic materials, especially copper iodide (CuI) and copper thiocyanate (CuSCN) as hole transport materials (HTMs) in perovskite solar cells (PSCs) for efficient, inexpensive and stable energy harvesting. Copper based films exhibit higher conductivity and wider-band-gap. The existing organic HTMs are expensive and have low hole mobility. The reported high power conversion efficiency (PCE) of CuI and CuSCN based perovskite solar cells are 6% and 20.3% respectively [Christians et al. J. Am. Chem. Soc., 2014, N Arora et al. Science 2017]. The perovskite solar cells based on inorganic CuI and CuSCN can be more stable and cost-effective with respect to spiro-OMeTAD HTM. We present our work on mixed perovskite in the form of (FAPbI3)0.85(MAPbBr3)0.15 in combination with CuI and CuSCN HTMs that lead to efficiencies 5.16% and 15.43% respectively in an n-i-p architecture under full sun illumination. The CuI based device displayed a short-circuit current density (Jsc) of 8.98 mA/cm2, Voc of 898.57 mV and fill factor (FF) of 0.64. Under similar conditions, the device with CuSCN, showed a significant increase in the Jsc (8.95 mA/cm2 to 20.86 mA/cm2) and Voc (from 898.57 mV to 1060 mV) (Figure1). A reference cell with standard spiro-OMeTAD HTM showed a PCE of 19.65% (with Voc of 1180 mV and Jsc of 22.70 mA/cm2). The high Jsc when using CuSCN with respect to CuI is mainly due to the effective charge extraction between the perovskite and CuSCN. However there is a strong quenching in the photoluminescence measurements in both CuI and CuSCN cases, which suggests that excellent hole injection is taking place from the perovskite active layer into the CuI and CuSCN hole transport materials (Figure 2). It is worth noting that CuI based perovskite devices showed a PCE of 6% with excellent photocurrent stability and 2 orders higher electrical conductivity that lead to higher fill factors [Christians et al. J. Am. Chem. Soc., 2014]. Impedance spectroscopy measurements revealed high recombination rate in CuI devices [Huangfu et al, Applied Surface Science 2015]. This could explain the low Voc and Jsc despite the quenching of the photoluminescence spectrum in the presence of CuI and CuSCN. Further studies are in progress in-order to find out the origin of the recombination and how to remediate them. Various device structure models (p-i-n and n-i-p geometry) with copper based HTMs are simulated with SCAPS software to find out the efficient structures with minimum losses. The results shows that the CuSCN based cells are more promising and can be used to prepare high efficiency perovskite solar cells. References J.A. Christians, R.CM. Fung, P.V. Kamat, J. Am. Chem. Soc. 2014, 136, 2, 758–764 pp. N. Arora, M. I. Dar, A. Hinderhofer, N. Pellet, F. Schreiber, S.M. Zakeeruddin, M. Grätzel, Science 2017,10.1126/science.aam5655. M. Huangfu, Y. Shen, G. Zhu, K. Xu and M. Cao*,F. Gu and L. Wang, Appl. Surf. Sci. 2015, 357-B, 2234–2240pp.

This study investigated the potential suitability of graphene quantum dots (GQD) and certain edge-functionalized GQDs (GQD-3Xs) as hole transport materials (HTMs) in perovskite solar cells (PSCs). The criteria for appropriate HTMs were evaluated, including solubility, hole mobility, light harvesting efficiency (LHE), exciton binding energy (Eb), hole reorganization energy (λh), hole mobility, and HTM performance. It was found that several of the compounds had higher hole mobility than Spiro-OMeTAD, a commonly used HTM in PSCs. The open circuit voltage and fill factor of the suitable GQD and GQD-3Xs were found to be within appropriate ranges for HTM performance in MAPbI3 PSCs. GQD-COOH and GQD-COOCH3 were identified as the most suitable HTMs due to their high solubility, small λh, and appropriate performance.

The development of highly efficient hole transport materials (HTMs) for perovskite solar cells (PSCs) has been a hot research topic. Acridine and its derivatives are gradually utilized as new blocks for optoelectronic applications, which stems from its rigid conjugated structure, shedding a new light on this old molecule. Meanwhile, its application in PSCs as a HTM has not been well explored, and the efficiency of 9,10-dihydroacridine (ACR)-based HTMs is relatively low. In this work, we conduct a systematic modulation of the peripheral substituents for ACR core building block-based HTMs and investigate the effects of the electron-donating ability and π-conjugation of peripheral groups on the photovoltaic performance of the corresponding HTMs. It is found that the peripheral groups with a weaker electron-donating ability and stronger π-conjugation are more suitable for the acridine core, which itself has a stronger electron-donating ability. Through molecular engineering, the newly developed HTM ACR-PhDM achieves an impressive power conversion efficiency of 23.5%. Our work lays the foundation for the design and development of efficient HTMs in the future.

Thermo-evaporated pentacene and perylene as hole transport materials for perovskite solar cells

Perovskite solar cells have gained immense interest from researchers owing to their good photophysical properties, low-cost production, and high power conversion efficiencies. Hole transport materials (HTMs) play a dominant role in enhancing the power conversion efficiencies (PCEs) and long diffusion length of holes and electrons in perovskite solar cells. In hole transport materials, modification of π-linkers has proved to be an efficient approach for enhancing the overall PCE of perovskite solar cells. In this work, π-linker modification of a recently synthesized H-Bi molecule (R) is achieved with novel π-linkers. After structural modifications, ten novel HTMs (HB1-HB10) with a D-π-D backbone are obtained. The structure-property relationship, and optoelectronic and photovoltaic characteristics of these newly designed hole transport materials are examined comprehensively and compared with reference molecules. In addition, different geometric parameters are also examined with the assistance of density functional theory (DFT) and time-dependent DFT. All the designed molecules exhibit narrow HOMO-LUMO energy gaps (Eg =2.82-2.99 eV) compared with the R molecule (Eg =3.05 eV). The designed molecules express redshifting in their absorption spectra with low values of excitation energy, which in return offer high power conversion efficiencies. Further, density of states and molecular electrostatic potential analysis is performed to locate the different charge sites in the molecules. The reorganizational energies of holes and electrons are found to have good values, suggesting that these novel designed molecules are efficient hole transport materials for perovskite solar cells. In addition, the low binding energy values of the designed molecules (compared with R) offer high current charge density. Finally, complex study of HB9:PC61 BM is also undertaken to understand the charge transfer between the molecules of the complex. The results of all analyses advocate that these novel designed HTMs are promising candidates for the construction of future high-performance perovskite solar cells.

The susceptibility of porphyrin derivatives to light-harvesting and charge-transport operations have enabled these materials to be employed in solar cell applications. The potential of porphyrin derivatives as hole-transporting materials (HTMs) for perovskite solar cells (PSCs) has recently been demonstrated, but knowledge of the relationships between the porphyrin structure and device performance remains insufficient. In this work, a series of novel zinc porphyrin (PZn) derivatives has been developed and employed as HTMs for low-temperature processed PSCs. Key to the design strategy is the incorporation of an electron-deficient pyridine moiety to down-shift the HOMO levels of porphyrin HTMs. The porphyrin HTMs incorporating diphenyl-2-pyridylamine (DPPA) have HOMO levels that are in good agreement with the perovskite active layers, thus facilitating hole transfers from the perovskite to the HTMs. The DPPA-containing zinc porphyrin-based PSCs gave the best performance, with efficiency levels comparable to those of PSCs using spiro-OMeTAD, a current state-of-the-art HTM. In particular, PZn-DPPA-based PSCs show superior air stability, in both doped and undoped forms, to spiro-OMeTAD based devices.

Side chain engineering and film uniformity: two key parameters for the rational design of dopant-free polymeric hole transport materials for efficient and stable perovskite solar cells

A series of conductive polymers, i.e., poly(3-methylthiophene) (PMT), poly(thiophene) (PT), poly(3-bromothiophene) (PBT) and poly(3-chlorothiophene) (PCT), were prepared via the electrochemical polymerization process. Subsequently, their application as hole-transporting materials (HTMs) in CH3NH3PbI3 perovskite solar cells was explored. It was found that rationally increasing the work function of HTMs proves beneficial in improving the open circuit voltage (Voc) of the devices with an ITO/conductive-polymer/CH3NH3PbI3/C60/BCP/Ag structure. In addition, the higher-Voc devices with a higher-work-function HTM exhibited higher recombination resistances. The highest open circuit voltage of 1.04 V was obtained from devices with PCT, with a work function of–5.4 eV, as the hole-transporting layer. Its power conversion efficiency attained a value of approximately 16.5%, with a high fill factor of 0.764, an appreciable open voltage of 1.01 V and a short circuit current density of 21.4 mA·cm–2. This simple, controllable and low-cost manner of preparing HTMs will be beneficial to the production of large-area perovskite solar cells with a hole-transporting layer.

The synthesis and characterization of a [Formula: see text]-phenylene-bridged ZnPc dimer along with a preliminary study of this material as hole transporting material (HTM) in perovskite solar cells is described. The maximum efficiencies that obtained are 15.2% for ZnPc-[Formula: see text]-ZnPc 1, thus demonstrating the potential of the Pc dimers that could pave the path to achieve highly efficient PSCs (PCE >20%).

Titanylphthalocyanine as hole transporting material for perovskite solar cells

Effect of dimethylamino substituent on tetraphenylethylene-based hole transport material in perovskite solar cells

Tuning electronic structures of thiazolo[5,4-d]thiazole-based hole-transporting materials for efficient perovskite solar cells