Linear-Shaped Low-Bandgap Asymmetric Conjugated Donor Molecule for Fabrication of Bulk Heterojunction Small-Molecule Organic Solar Cells.

A linear-shaped small organic molecule (E)-4-(5-(3,5-dimethoxy-styryl)thiophen-2-yl)-7-(5″-hexyl-[2,2':5',2″-terthiophen]-5-yl)benzo[c][1,2,5]thiadiazole (MBTR) comprising a benzothiadiazole (BTD) acceptor linked with the terminal donors bithiophene and dimethoxy vinylbenzene through a π-bridge thiophene was synthesized and analyzed. The MBTR efficiently tuned the thermal, absorption, and emission characteristics to enhance the molecular packing and aggregation behaviors in the solid state. The obtained optical bandgap of 1.86 eV and low-lying highest occupied molecular orbital (HOMO) level of -5.42 eV efficiently lowered the energy losses in the fabricated devices, thereby achieving enhanced photovoltaic performances. The optimized MBTR:PC71BM (1:2.5 w/w%) fullerene-based devices showed a maximum power conversion efficiency (PCE) of 7.05%, with an open-circuit voltage (VOC) of 0.943 V, short-circuit current density (JSC) of 12.63 mA/cm2, and fill factor (FF) of 59.2%. With the addition of 3% 1,8-diiodooctane (DIO), the PCE improved to 8.76% with a high VOC of 1.02 V, JSC of 13.78 mA/cm2, and FF of 62.3%, which are associated with improved charge transport at the donor/acceptor interfaces owing to the fibrous active layer morphology and favorable phase separation. These results demonstrate that the introduction of suitable donor/acceptor groups in molecular design and device engineering is an effective approach to enhancing the photovoltaic performances of organic solar cells.

Gamma Knife Radiosurgery for Incidental, Symptomatic Unruptured, and Ruptured Brain Arteriovenous Malformations.

BACKGROUND: This study was performed to investigate clinical characteristics and outcome after gamma knife radiosurgery (GKS) in patients with incidental, symptomatic unruptured, or ruptured arteriovenous malformations (AVMs). METHODS: A total of 491 patients with brain AVMs treated with GKS from June 2002 to September 2017 were retrospectively reviewed. All patients were classified into the incidental (n = 105), symptomatic unruptured (n = 216), or ruptured AVM (n = 170) groups. RESULTS: The mean age at diagnosis of incidental, symptomatic unruptured, and ruptured AVMs was 40.3, 36.7, and 27.6 years, respectively. The mean nidus volume was 3.9, 5.7, and 2.4 cm3, respectively. Deep venous drainage was identified in 34, 54, and 76% patients, respectively. There were no significant differences in obliteration rates after GKS between the 3 groups (64.8, 61.1, and 65.9%, respectively) after a mean follow-up period of 60.5 months; however, patients with incidental AVM had a significantly lower post-GKS hemorrhage rate than patients with symptomatic unruptured or ruptured AVMs (annual hemorrhage rate of 1.07, 2.87, and 2.69%; p = 0.028 and p = 0.049, respectively). CONCLUSIONS: There is a significant difference in clinical and anatomical characteristics between incidental, symptomatic unruptured, and ruptured AVMs. The obliteration rate after GKS is not significantly different between the 3 groups. Meanwhile, an older age at diagnosis and lower hemorrhage rate after GKS in incidental AVMs suggest that they have a more indolent natural course with a lower life-long risk of hemorrhage.

Photocurrent induced by conducting channels of hole transporting layer to adjacent photoactive perovskite sensitized TiO2 thin film: solar cell paradigm.

A high performance perovskite solar cell was fabricated using the distinguished morphology of polyaniline nanoparticles (PANI-NPs) as an efficient hole transporting layer (HTL) with methylammonium lead iodide perovskite (CH3NH3PbI3) as sensitizer. PANI-NPs were simply synthesized by the oxidative chemical polymerization of aniline monomer at 0-5 °C. A reasonable solar-to-electricity conversion efficiency of ∼6.29% with a high short circuit current (JSC) of ∼17.97 mA/cm(2) and open circuit voltage (VOC) of ∼0.877 V were accomplished by Ag/PANI-NPs/CH3NH3PbI3/mp-anatase-TiO2/bl-TiO2/FTO perovskite solar cell. The transient photocurrent and photovoltage studies revealed that the fabricated solar cell showed better charge transport time, diffusion coefficient, diffusion length, and charge collection efficiency. Herein, the use of PANI-NPs as the HTL improved the charge carrier generation and the charge collection efficiency of the fabricated solar cell.

Fast one-step method to synthesize TiO2 nanoparticle clusters for dye sensitized solar cells.

We have successfully designed a rapid method for producing dye sensitized solar cells (DSSC) using TiO2 films prepared by a modified dielectric barrier discharge jet (m-DBD jet) method which uses a DBD jet with elevated substrate temperatures from room temperature (RT) to 500 degrees C for approximately 10 min. This facile process has several advantages over other methods such as (1) eliminating additional coating and annealing steps, (2) creating films with high speed electron mobility via hierarchical pore clusters, and (3) allowing controlled TiO2 bandgap by N doping using atmospheric nitrogen instead of supplying N2 gas. Depending on reaction conditions, the resulting nanostructured materials have various sizes and shapes, with those deposited at the highest substrate temperatures displaying hierarchical walnut-shaped morphology as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A possible growth mechanism of TiO2 nanoparticle clusters (TNC) is presented and discussed. Finally, this m-DBD jet method produces TNC films that exhibit approximately 4 times higher photo-conversion efficiency than the nanoparticle films by the unmodified DBD jet method.

Fabrication and growth mechanism of ZnO nanostructures and their cytotoxic effect on human brain tumor U87, cervical cancer HeLa, and normal HEK cells.

ZnO nanostructures of diverse shape were grown via a solution process with different precursors and conditions. Morphological investigation of the nanostructures was carried out using field emission scanning electron microscopy and transmission microscopy observations and revealed that the nanostructures exhibit a wurtzite phase with an ideal lattice fringe distance of approximately 0.52 nm. The powder crystallinity was examined via X-ray diffraction spectroscopy. Screening results from anticancer studies of the effects on human brain tumor U87, cervical cancer HeLa, and normal HEK cells of ZnO nanostructures of diverse shape were obtained and indicate promising activity that varies with changes in the structure and the size of the particles. Treatment-induced cell death [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and survival assay], growth inhibition, cytogenetic damage (formation of micronuclei), and apoptosis were studied as parameters for the cellular response. Treatment with nanostructures enhanced growth inhibition and cell death in a concentration-dependent manner in both U87 and HeLa cell lines. At higher concentrations (above 15.6 µg/ml) the cytotoxic effects of the nanoparticles were highly synergistic and mainly mediated through apoptosis, implying the possible interactions of lesions caused by the agents. The enhanced cell death due to nanoparticles was accompanied by a significant increase (2-3 fold at 31.25 µg/ml) in the formation of micronuclei in U87 cells. The increase in the formation of micronuclei observed after treatment indicates that these structures may interfere with the rejoining of DNA strand breaks. Among all the nanostructures, nanoparticles and sheets exhibited potent activity against both HeLa and U87 cells. However, despite potent in vitro activity, all nanostructures exhibited diminished cytotoxicity against normal human HEK cells at all effective concentrations.

Microbial synthesis of gold nanoparticles using the fungus Penicillium brevicompactum and their cytotoxic effects against mouse mayo blast cancer C 2 C 12 cells.

Microorganisms, their cell filtrates, and live biomass have been utilized for synthesizing various gold nanoparticles. The shape, size, stability as well as the purity of the bio synthesized nanoparticles become very essential for application purpose. In the present study, gold nanoparticles have been synthesized from the supernatant, live cell filtrate, and biomass of the fungus Penicillium brevicompactum. The fungus has been grown in potato dextrose broth which is also found to synthesize gold nanoparticles. The size of the particles has been investigated by Bio-TEM before purification, following purification and after storing the particles for 3 months under refrigerated condition. Different characterization techniques like X-ray diffraction, Fourier transform infrared spectroscopy, and UV-visible spectroscopy have been used for analysis of the particles. The effect of reaction parameters such as pH and concentration of gold salt have also been monitored to optimize the morphology and dispersity of the synthesized gold nanoparticles. A pH range of 5 to 8 has favored the synthesis process whereas increasing concentration of gold salt (beyond 2 mM) has resulted in the formation of bigger sized and aggregated nanoparticles. Additionally, the cytotoxic nature of prepared nanoparticles has been analyzed using mouse mayo blast cancer C(2)C(12) cells at different time intervals (24, 48, and 72 h) of incubation period. The cells are cultivated in Dulbecco's modified Eagle's medium supplemented with fetal bovine serum with antibiotics (streptopenicillin) at 37°C in a 5% humidified environment of CO(2). The medium has been replenished every other day, and the cells are subcultured after reaching the confluence. The viability of the cells is analyzed with 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method.

Effects of the dichloromethane fraction of Dipsaci Radix on the osteoblastic differentiation of human alveolar bone marrow-derived mesenchymal stem cells.

Dipsaci Radix is the dried root of Dipsacus asper Wall. It has been used in Korean herbal medicine to treat bone fractures. In this study, we examined the effect of the dichloromethane fraction of Dipsaci Radix (DR(DM)) on the osteoblastic differentiation of human alveolar bone marrow-derived MSCs (ABM-MSCs). The ABM-MSCs were isolated from healthy subjects and cultured in vitro, followed by phenotypic characterization. They showed a fibroblast-like morphology and expressed CD29, CD44, CD73, and CD105, but not CD34. Calcified nodules were generated in response to both dexamethasone (DEX) and DR(DM). There was a significant increase in the alkaline phosphatase (ALP) activity and protein expression of bone sialoprotein (BSP) and osteocalcin (OC) in response to DEX and DR(DM) as compared to control. These results provide evidence for the osteogenic potential of cultured ABM-MSCs in response to DR(DM). Also, an active single compound was additionally isolated from DR(DM). The single compound (hederagenin 3-O-(2-O-acetyl)-α-L-arabinopyranoside) also significantly increased ALP activity and the level of protein expression of BSP and OC. These results highlight the possible clinical applications of DR(DM) and hederagenin 3-O-(2-O-acetyl)-α-L-arabinopyranoside in bone regeneration.

Electrical and structural characterization of plasma polymerized polyaniline/TiO2 heterostructure diode: a comparative study of single and bilayer TiO2 thin film electrode.

A heterostructure was fabricated using p-type plasma polymerized polyaniline (PANI) and n-type (single and bilayer) titanium dioxide (TiO2) thin film on FTO glass. The deposition of single and bilayer TiO2 thin film on FTO substrate was achieved through doctor blade followed by dip coating technique before subjected to plasma enhanced polymerization. To fabricate p-n heterostructure, a plasma polymerization of aniline was conducted using RF plasma at 13.5 MHz and at the power of 120 W on the single and bilayer TiO2 thin film electrodes. The morphological, optical and the structural characterizations revealed the formation of p-n heterostructures between PANI and TiO2 thin film. The PANI/bilayer TiO2 heterostructure showed the improved current-voltage (I-V) characteristics due to the substantial deposition of PANI molecules into the bilayer TiO2 thin film which provided good conducting pathway and reduced the degree of excitons recombination. The change of linear I-V behavior of PANI/TiO2 heterostructure to non linear behavior with top Pt contact layer confirmed the formation of Schottky contact at the interfaces of Pt layer and PANI/TiO2 thin film layers.

Urea sensing characteristics of titanate nanotubes deposited by electrophoretic deposition method.

Urea sensing properties of titanate nanotubes (TNT) are presented here. TNT films were deposited by electrophoretic deposition (EPD) method on aluminum substrate. Prior to EPD, commercial nanoparticles of TiO2 were hydrothermally treated at 70 degrees C for 48 h after sonicating the solution for 8 h. Hydrothermal method resulted in the conversion of particles to tubular structure following the established method. Urease was covalently attached with TNT (by soaking in urease solution for 3 h). In general, conductivity of film increases after urease immobilization. The urease immobilized films were characterized for urea sensing in the concentration range of 1 mM to 500 mM. Three different sensitivity regions are observed viz. (i) lower concentrations (below 10 mM); (ii) linear region up to 100 mM and a (iii) saturation region above 100 mM. Sensors are extremely sensitive in region (i). From the elemental analyses of the films after urease immobilization, urease was found attached with TiO2, as evident by N 1s peak in the photoelectron spectra. Cyclic voltammetric studies indicated surface-confined redox couple is responsible for sensing behavior. A possible sensing mechanism is presented and discussed.

Diode behavior of electrophoretically deposited polyaniline on TiO2 nanoparticulate thin film electrode.

An inorganic/organic hetrostructure diode was constructed by the electrophoretic deposition of the p-type polyaniline (PANI) on an n-type titanium oxide (TiO2) nanoparticulate thin film. The bonding and internalization of PANI to TiO2 nanoparticulate thin film were confirmed by the morphological, structural and optical studies of electrophoretically deposited PANI/TIO2 nanoparticulate thin film. The increased size of TiO2 nanoparticles indicated the well penetration of PANI molecules into the pores of mesoporous TiO2 nanoparticulate thin film. The XPS studies of PANI/TiO2 heterostructure exhibited the surface bonding and interaction between PANI molecules and TiO2 nanoparticles. The current-voltage (I-V) characterization of PANI/TiO2 heterostructure was carried out in the forward and the reverse bias at the applied voltage ranges from -1 V to +1 V with a scan rate of 2 mV/s. The constructed Pt/PANI/TiO2 heterostructure device established diodic behavior with non-linear nature of I-V curves.

Synthesis and characterization of polyaniline/MCM-41 nanocomposites and their photocatalytic activity.

The novel organic-inorganic nanocomposites were synthesized via in-situ polymerization of polyaniline (PANI) with mesoporous silica (MCM-41) for methylene blue (MB) dye degradation under visible light. The synthesized PANI/MCM-41 nanocomposites were characterized through Fourier transform infrared (FTIR), X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and UV-visible studies. The structural and optical properties confirmed the interaction between PANI and MCM-41. The photocatalytic experiments showed that the MB dye was efficiently degraded by approximately 70% under light irradiation over the surface of the PANI/MCM-41 nanocomposites. The degradation might occur due to the efficient charge separation of the e(-)-h+ pairs at the interface of PANI and MCM-41 in the excited state under light irradiation.

Synthesis and characterization of high-purity silica nanosphere from rice husk.

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.

Rapid Spontaneous Resolution of Large Acute Subdural Hematoma.

Usually, acute subdural hematomas (ASDHs) result from head trauma and require urgent surgical treatment. However, there have been many reports of rapid spontaneous resolution of ASDHs since 1986. Recently, we experienced a case of a massive ASDH that resolved spontaneously within 1.5 days. A 76-year-old man was admitted to a local hospital after a head injury. According to his clinical records, his initial neurologic status was good (Glasgow Coma Scale score of 14). However, his head computer tomography (CT) scan demonstrated a massive ASDH to the right, with a significant midline shift. Based on his neurological status and general condition, surgery was not considered, and the patient was closely monitored in the intensive care unit. The next day, the patient was transferred to our hospital as requested by his family, after which his neurological state stabilized, and the customary follow-up brain CT was performed. It was about 32 hours after the patient's head injury, and it revealed an unexpected finding, near-total resolution of the ASDH. Herein, we review previously reported similar cases and relevant mechanisms of rapid resolution of the ASDH. We believe that neurosurgeons should comprehensively assess the patient's condition and CT findings and provide appropriate treatment, especially when surgical intervention is unnecessary.

Enticing 3D peony-like ZnGa2O4 microstructures for electrochemical detection of N, N-dimethylmethanamide chemical.

We demonstrate the hydrothermal synthesis of three dimension (3D) peony-like morphology of zinc gallate (ZnGa2O4), dominated by assembled nanosheets and applied as electrode material in electrochemical detection of N,N-dimethylmethanamide chemical. The crystalline, structural and compositional characterizations deduced the formation of high quality ZnGa2O4 with spinal crystal structure. Peony-like 3D ZnGa2O4 was benefited by a high surface area of ~62.3 m2 g-1, good pore distribution (mean pore diameter of ~23.3 nm) and large pore volume of ~0.3622 cm3 g-1. N,N-dimethylmethanamide chemical sensor based on peony-like 3D ZnGa2O4 electrode presented a linear curve in the working dynamic range of 1 nM-10 mM. Significantly improved chemical sensitivity of ~154.2 mA mM-1 cm-2 with low detection limit value of ~0.14 µM were achieved. The fabricated sensor based on peony-like 3D ZnGa2O4 electrode endorsed real sample analysis and ascertained the selectivity towards N,N-dimethylmethanamide chemical by analyzing a range of interfering analytes, viz. ethanol, tetrahydrofuran, methyl amine chemical.

Antibacterial activity of ZnO nanoparticles prepared via non-hydrolytic solution route.

The antibacterial activity of ZnO nanoparticles has been investigated and presented in this paper. Nanoparticles were prepared via non-hydrolytic solution process using zinc acetate di-hydrate (Zn(CH(3)COO)(2).2H(2)O) and aniline (C(6)H(5)NH(2)) in 6 h refluxing at approximately 65 degrees C. In the presence of four pathogens such as Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, and Klebsiella pneumoniae, the antibacterial study of zinc oxide nanoparticles were observed. The antibacterial activity of ZnO nanoparticles (ZnO-NPs) were studied by spectroscopic method taking different concentrations (5-45 microg/ml) of ZnO-NPs. Our investigation reveals that the lowest concentration of ZnO-NPs solution inhibiting the growth of microbial strain is found to be 5 microg/ml for K. pneumoniae, whereas for E. coli, S. aureus, and S. typhimurium, it was calculated to be 15 microg/ml. The diameter of each ZnO-NPs lies between "20 and 30 nm" as observed from FESEM and transmission electron microscopy images. The composition of synthesized material was analyzed by the Fourier transform infrared spectroscopy, and it shows the band of ZnO at 441 cm(-1). Additionally, on the basis of morphological and chemical observations, the chemical reaction mechanism of ZnO-NPs was also proposed.

CYFRA 21-1 levels in cerebrospinal fluid as a putative therapeutic monitoring biomarker for patients with leptomeningeal carcinomatosis: A pilot study.

BACKGROUND: To investigate the feasibility of cerebrospinal fluid (CSF) CYFRA 21-1 levels as a therapeutic monitoring biomarker in leptomeningeal carcinomatosis (LMC) patients undergoing ventriculo-lumbar perfusion (VLP) chemotherapy. METHODS: The levels of CYFRA 21-1 in 42 CSF samples from 15 LMC patients were analyzed using an electrochemiluminescence immunoassay. Samples were collected at individual time points during VLP chemotherapy. Therapeutic outcomes were measured as improvements in the Karnofsky Performance Status (KPS) score and decreasing intracranial pressure (ICP) as the main endpoint of VLP chemotherapy. Changes in CSF CYFRA 21-1 levels, protein levels, and cytology results were also investigated. We subsequently evaluated whether these changes were correlated with KPS score and ICP. RESULTS: The CSF CYFRA 21-1 levels at individual time points were associated with KPS score and ICP. The KPS scores (p= 0.007) and ICP (p= 0.018) of patients with high CSF CYFRA 21-1 levels were significantly different from those of patients with low CSF CYFRA 21-1 levels. By contrast, CSF protein levels and cytological responses were not significantly associated with KPS scores and ICP. CONCLUSIONS: CSF CYFRA 21-1 may have utility as a therapeutic monitoring biomarker to design personalized therapeutic strategies in LMC patients undergoing VLP chemotherapy.

Highly sensitive chemiluminescence enzyme immunoassay for the quantification of carcinoembryonic antigen in the presence of an enhancer and a stabilizer.

Using the advantages of phenol red, a signal enhancer, and bovine serum albumin (BSA), a stabilizer of horseradish peroxidase (HRP), added in HRP enzyme reaction of Amplex Red and H2O2, highly sensitive 1,1'-oxalyldiimidazole chemiluminescence enzyme immunoassay (ODI-CLEIA) was developed to rapidly quantify trace levels of carcinoembryonic antigen (CEA) in human serum. Phenol red acts as an enhancer in ODI-CLEIA while BSA supported rapid and stable activation of HRP. The CL emission of resorufin formed from the HRP enzyme reaction in the presence of BSA and phenol red was about 70-fold brighter than that in the absence of both materials. ODI-CLEIA in the presence of BSA (1.5 mg/ml).and phenol red (1 mM) was able to rapidly analyze CEA in human serum with the wide linear calibration curve (2.5-100 ng/ml). The limit of detection (LOD = 3σ/slope) of ODI-CLEIA was as low as 0.19 ng/ml. Additionally, it was confirmed that the accuracy, precision, and reproducibility of ODI-CLEIA in the presence of BSA and phenol red were good with the statistically acceptable error range.

Glucose sensor based on nano-baskets of tin oxide templated in porous alumina by plasma enhanced CVD.

A feasibility study of glucose oxidase (GOx) immobilized tin oxide thin films, consisting of nano-baskets, for glucose sensing is presented. The nano-baskets of SnO(2) were grown on in-house fabricated anodized aluminum oxide pores of approximately 80-nm diameter using plasma enhanced chemical vapor deposition (PECVD) at an RF power of 60W. Hydrated stannic chloride was used as a precursor and O(2) (20 sccm) as a reactant gas. The deposition was carried out from 350 to 450 degrees C at a pressure of 0.2 Torr for 15 min each. Deposition at 450 degrees C resulted in crystalline film with basket-like (nano-sized) structure. GOx was immobilized by physical adsorption (soaking films in GOx solution containing 1000 units for 3h). Increase in film conductivity was noticed after GOx immobilization. The immobilized films were found sensitive to glucose (C(2)H(12)O(6), dextrose) concentration from 10 to 360 mg/dl. Sensitivity increases linearly with glucose concentration. Nano-baskets resulted in higher sensitivity in comparison with other structures. From the elemental analyses of the films after GOx immobilization, GOx was found covalently attached with tin oxide, as evident by N 1s peak in the photoelectron spectra. A possible sensing mechanism is presented and discussed.

A novel perovskite solar cell design using aligned TiO2 nano-bundles grown on a sputtered Ti layer and a benzothiadiazole-based, dopant-free hole-transporting material.

This work highlights the utilization of a novel hole-transporting material (HTM) derived from benzothiadiazole: 4-(3,5-bis(trifluoromethyl)phenyl)-7-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole (CF-BTz-ThR) and aligned TiO2 nano-bundles (TiO2 NBs) as the electron transporting layer (ETL) for perovskite solar cells (PSCs). The aligned TiO2 NBs were grown on titanium (Ti)-coated FTO substrates using a facile hydrothermal method. The newly designed CF-BTz-ThR molecule with suitable highest occupied molecular orbital (HOMO) favored the effective hole injection from perovskite deposited aligned TiO2 NBs thin film. The PSCs demonstrated a power conversion efficiency (PCE) of ∼15.4% with a short circuit current density (Jsc) of ∼22.42 mA cm-2 and an open circuit voltage (Voc) of ∼1.02 V. The efficiency data show the importance of proper molecular engineering whilst highlighting the advantages of dopant-free HTMs in PSCs.

Perovskite Solar Cells: Influence of Hole Transporting Materials on Power Conversion Efficiency.

The recent advances in perovskite solar cells (PSCs) created a tsunami effect in the photovoltaic community. PSCs are newfangled high-performance photovoltaic devices with low cost that are solution processable for large-scale energy production. The power conversion efficiency (PCE) of such devices experienced an unprecedented increase from 3.8 % to a certified value exceeding 20 %, demonstrating exceptional properties of perovskites as solar cell materials. A key advancement in perovskite solar cells, compared with dye-sensitized solar cells, occurred with the replacement of liquid electrolytes with solid-state hole-transporting materials (HTMs) such as 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), which contributed to enhanced PCE values and improved the cell stability. Following improvements in the perovskite crystallinity to produce a smooth, uniform morphology, the selective and efficient extraction of positive and negative charges in the device dictated the PCE of PSCs. In this Review, we focus mainly on the HTMs responsible for hole transport and extraction in PSCs, which is one of the essential components for efficient devices. Here, we describe the current state-of-the-art in molecular engineering of hole-transporting materials that are used in PSCs and highlight the requisites for market-viability of this technology. Finally, we include an outlook on molecular engineering of new functional HTMs for high efficiency PSCs.