K. S. Rahman

Influence of thermal annealing on CdTe thin film deposited by thermal evaporation technique

Effects of thermal annealing on the structural and optical properties of thermally evaporated CdTe thin films are presented here. Thin films of CdTe were deposited on soda lime glass substrates at room temperature by varying the deposition current ranging from 25 Amperes to 30 Amperes by thermal evaporation. The grown samples were annealed at the annealing temperature of 400°C for 15 minutes in a vacuum furnace of nitrogen ambient with pressure of 250–300 mTorr. The structural, optical and electrical properties of the grown samples were investigated by XRD, AFM and UV-VIS spectrometry. The as-deposited films prepared at deposition current 25A shows polycrystalline nature whereas the films prepared at 28A and 30A exhibit cubic crystallinity with (111) preferential orientation around 2θ=23.8°. The surface roughness of the films is also highly affected by the thermal annealing as observed from the AFM images. The band gap has been found around 1.5 eV for the as-deposited film whereas the band gap decreased approximately to 1.4 eV after thermal annealing treatment.

Effect of p-type transition metal dichalcogenide molybdenum ditelluride (p-MoTe 2 ) layer formation in Cadmium Telluride solar cells from numerical analysis

In this paper, we have investigated the effects of transition metal dichalcogenide namely Molybdenum ditelluride (MoTe2) layer formation in between Cadmium Telluride (CdTe) absorber layer and Mo back contact from numerical modeling. The main purpose was to investigate the possible effects of p-type MoTe2 in CdTe thin film solar cell. Energy band line-up in the vicinity of Mo/MoTe2/CdTe interface is investigated to explain the interface properties in terms of various parameters. It was found that p-type MoTe2 has some effects to the performance of CdTe thin film solar cells. Thickness, bandgap energy and carrier concentration of p-MoTe2 all have been varied in the numerical simulation to observe its effects on the cell performance. It was found that when thickness of MoTe2 is less than 20 nm, the cell efficiency decreases, which may be due to the shunting caused by the thinner p-MoTe2. Furthermore, the increase in MoTe2 bandgap results in unfavorable effect to the performance of the cell mainly due to the possibility of electrons to drift towards the back contact and recombination. The increase of the carrier concentration improves the cell performance. This could be attributed to the less recombination of electrons as well as less built in potential (Vbi) at MoTe2/CdTe junction.

Solar Photovoltaic Technologies: From Inception Toward the Most Reliable Energy Resource

The ever-increasing global energy needs due to continual population growth, imminent depletion of fossil fuels, as well as mitigating environmental pollutions around the globe have compelled mankind to search for alternatives in recent years. Among many known alternatives, solar photovoltaic (PV) technology has undoubtedly proven itself worth as one of the mainstream renewable energy resources for its various merits. Solar photovoltaic technology is capable to fit into any requirements with freedom in scalability from milli-watt to almost giga-watt range of demand and response. In years, solar PV technology has shown its inherent potential with versatility in material usage, diversified capability in energy production, as well as sustainability with minimal or almost no adverse environmental effect. This chapter will present the chronological history of the most potential solar PV technologies from the discovery of the science as “photovoltaic PV effect” through the journey of the technological development toward becoming the most reliable energy resource of the near future.

Close‐Spaced Sublimation (CSS): A Low‐Cost, High‐Yield Deposition System for Cadmium Telluride (CdTe) Thin Film Solar Cells

Semiconductors are the key materials in many of our modern day devices, such as sensors, integrated circuits, energy harvesting devices, optoelectronics and so on. However, apart from two known elemental semiconductors that are silicon and germanium, we have been using many of the synthesized ones since the microelectronic revolution known as invention of transistor. Numerous compound semiconductors since then have been synthesized, grown, deposited or simply fabricated by numerous processes in the scientific community. To avoid associated chemical disposals or keep safe from toxic or combustible gas usages in any semiconductor fabrication facilities, many researchers choose physical vapor deposition as the simplest method. One of such processes is called Close-Spaced Sublimation (CSS), which is a kind of thermal evaporation by nature. This chapter would give a comprehensive outline on CSS as one of the most advantageous semiconductor deposition processes for many compound semiconductors having relatively low evaporation temperature. Cadmium telluride (CdTe) is one of the examples utilized for solar cell absorber materials since the early 1980s using CSS technique. Therefore, growth of CdTe thin films by CSS and its utilization in thin film solar cells will be discussed to comprehend the ultimate benefits of the close-spaced sublimation (CSS) process.

An investigation on copper doping to CdTe absorber layers in CdTe thin film solar cells

Polycrystalline Cadmium Telluride (CdTe) is the most stable compound that melts congruently. This leads to the feasibility of multiple methods of deposition, which consistently produce stoichiometric thin film CdTe. On the other hand, this has become a disadvantage of CdTe due to the tendency of self-compensation and limiting the doping capability hence limiting the improvement of solar cells efficiency and open-circuit voltage. AMPS 1D simulation of CdTe conventional device structure indicates significant open-circuit voltage improvement with effective acceptor concentration >1015 cm−3. Copper has been utilized commonly as p-type dopant in the R&D of CdTe thin film solar cells. In this work, different copper concentration were examined and introduced to CdTe thin film absorbers. Controlled amount of Cu were applied in solution form prior to the back contact formation process. The solar cells efficiency and open-circuit voltage indicate that doping of Cu in CdTe has an optimum range that limits the effective acceptor concentration. Exceeding the optimum concentration has adverse impact to efficiency and open-circuit voltage due to self-compensation. Short-circuit current density and fill factor saturates at high Cu concentration. This suggests that the method of Cu doping application through CdTe thin film surface has a saturation level.

Solar powered ferry boat for the rural area of Bangladesh

Bangladesh is a riverine country. Ferry boats are the major means of communication in the rural area. Diesel is used as the fuel in the engine boats used for transporting people from one side of a river bank to the other. To avoid environmental pollution solar powered boat is proposed. A conventional ferry boat is converted into solar powered ferry boat. A complete design process is described in this paper. Following the design process, the boat has been retrofitted with 48V, 500W BLDC motor, 1kW Solar panel with 9600 VAh Battery. The boat is 6.5 meter long and 2 meter beam, capable of carrying 1200kg load for 8 hours. The approximate speed of the boat is measured as 3knots, which is capable of covering 60 km distance in one full charge.

Nanostructured and wide bandgap CdS:O thin films grown by reactive RF sputtering

In this study, CdS:O thin films were prepared from a 99.999% CdS target by reactive sputtering in a Ar:O2 (99:1) ambient with different RF power at room temperature. The deposited films were studied by means of XRD, SEM, EDX, Hall Effect and UV-Vis spectrometry. The incorporations of O2 into the films were observed to increase with the decrease of deposition power. The cryatallinity of the films were reduced, whereas the band gaps of the films were increased by the increase of O2 content on the films. The films were found in nano-structured grains with a compact surface. It has been seen that the highest carrier density is observed in the film with O2 at.% 21.10, while the values decreased with the further increase or decrease of O2 content on the films; indicating that specific amount of donor like O2 atoms substitute to the S atoms can improve the carrier density of the CdS:O thin film.