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Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon over a wide temperature range (25–500 K) is extended, to include previously neglected carrier transitions between localized states. In addition to free carrier capture (emission) transitions into (from) localized states, we include the process of electron hopping in conduction band tail states. Exponential distributions are assumed for both conduction and valence band tail states, while the dangling bond defect distribution is calculated in accordance with the defect pool model. Localized to extended state transitions follow the Simmons and Taylor statistics, and localized to localized state transitions involve electron hopping between nearest neighbour sites. Comparison with simulations in the absence of electron hopping reveals a smooth transition around 110 K, between regions of (high temperature) extended state conduction and (low temperature) hopping conduction. A hopping transport energy level is identified as the peak of the energy distribution of the hopping photocarriers, and shows a temperature dependence in agreement with existing theoretical work.

Considering the thiophene unit as an electron-rich heterocycle, it is investigated with the aim of elucidating its potential efficiency for solar cell application. With the introduction of active substituents such as COOEt, CONH 2 and CN into the thiophene segment, three novel thieno pyridine sensitizers (6a-c), based on donor-acceptor D-π-A construction, are designed and synthesized. The effect of the anchoring groups is investigated based on their molecular orbital's (MO's) energy gap (E g ). The electrostatic interaction between the synthesized dyes and metal nanoparticles, namely gold, silver and ruthenium, is believed to improve their performance as organic sensitizers. The dye-sensitized solar cells (DSSCs) are manufactured using the novel diazenyl pyridothiophene dyes, along with their metal nanoparticles conjugates as sensitizers, and were examined for efficiency improvement. Accordingly, using this modification, the photovoltaic performance was significantly improved. The promising results of conjugate (6b/AgNPs), compared with reported organic and natural sensitizers (J SC (1.136 × 10 −1 mA/cm 2 ), V OC (0.436 V), FF (0.57) and η (2.82 × 10 −2 %)), are attributed to the good interaction between the amide, methyl, amino and cyano groups attached to the thiophene pyridyl scaffolds and the surface of TiO 2 porous film. Implementation of a molecular modeling study is performed to predict the ability of the thiophene moiety to be used in solar cell applications.Molecules 2020, 25, 1813 2 of 18 the TiO 2 photoanode conduction band (i.e., the semiconductor and oxidized molecules) through the anchoring/acceptor group adsorbed on its surface (i.e., a cyano, carboxylic or phosphonic group) [6,7]. The sensitizer is illuminated by the light; thus, the excited electrons will transfer from donor to acceptor terminals through the π-conjugation bridge and then inject into the conduction band. The design and mechanism of organic sensitizers for DSSCs have been explained in detail by Obotowo et al. [8].The efficiency of a DSSC as light harvesting matter depends mainly on the nature and the amount of the adsorbed dye molecules on the photoanode [9,10] and the thickness of the photoanode as well [11]. To achieve the most optimized D-π-A dyes, they should be designed for broader absorption in the near IR region, minimizing the energy level mismatch between the oxidation potential of the dye's excited state and TiO 2 conduction band, and the HOMO and electrolyte as well, reducing the rate of charge recombination at the photoanode-electrolyte interface, prohibiting dye aggregation and increasing the stability of the DSSC [6]. Thiophene derivatives (e.g., bithiophenes [5], oligo thiophenes [5], aryl thiophenes [12] and aryl bithiophenes [13]) have attracted the attention of many researchers to synthesize donor-acceptor substituted π-conjugated systems, such as formyl π-conjugated systems, through cross-coupling/metalation followed by DMF quenching [5] and Vilsmeier-Haack-Arnold formylation reactions [13,14]. Plasmon resonance ...

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Dark and illuminated current–voltage (J–V) characteristics of the hydrogenated amorphous silicon (a-Si:H) p–i–n diode have been simulated by solving numerically the full set of transport equations. The dependence of the dark current on the intrinsic layer (i-layer) thickness and on the measurement temperature is investigated by taking into account the presence of the p/i interface defect states. Good agreement with experimental data is obtained when the p/i interface defect density is increased with increasing i-layer thickness. Further, no appreciable influence was remarked for the i/n interface states on the J–V characteristic, which is in agreement with experimental observations. The numerical simulation also concerned the evaluation of the diode photo-parameters, i.e. the short-circuit current density (Jsc) and the open-circuit voltage (Voc), and reproduced, in a good manner, the light intensity dependence of Jsc and Voc for different i-layer thicknesses.

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This paper is concerned with the numerical simulation of the defect density influence on the steady state response of a silicon-based p-i-n cell under reverse bias dark conditions. To show this effect, the numerical simulation is performed on a crystalline cell containing a single discrete level of defects in the energy gap and in which the density of defects is varied. Afterwards, we extend our model to a typical amorphous silicon cell by including band tails and dangling bonds. The density of dangling bonds is calculated according to the defect pool model. For both cases, a detailed description of the physical model and its mathematical formulation is presented. By analysing the different variables which describe the electrical behaviour of the cell in the steady state such as the free carrier distributions, the carrier lifetimes and the quasi-Fermi levels, we show how the density of defects changes the semiconductor regime from lifetime to relaxation.