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We study light trapping in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on various nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. We have investigated the correlation between the back reflector optical properties and the corresponding solar cell performance. We have introduced double size polystyrene sphere patterned back reflectors and have provided experimental evidence for improved light trapping performance compared to single size polystyrene sphere patterned back reflectors. We have achieved high performing nanostructured amorphous silicon solar cells with an initial power conversion efficiency of 7.53% and over 20% enhancement of the short-circuit current compared with the reference flat solar cell.

Electric vehicle (EV) becomes an important option to overcome limited resources of fossil energy resources and to reduce side effects of Internal Combustion Engine Vehicles (ICEV) on the environment and health. However, the implementation policy of EV needs to apply carefully to make this policy sustainable and to minimize its side effects. Therefore, the Government of a country plays a significant role in leading and support the implementation of EV with policy and regulation. This paper reviews policies of Electric Vehicles (EV) in South Korea and Indonesia. The main objective of this review is to evaluate the strengths and weaknesses of the policies implemented in those countries. Three main aspects are elaborated, i.e., the main policy, the technology, and the private sector implementations. This paper also develops recommended policies and actions that could be done in Indonesia by reflecting on the EV policy in South Korea.

We have prepared solution processed V2Ox and WOx (s-V2Ox and s-WOx) thin films as hole selective contacts for Si solar cell applications. The material properties of s-V2Ox and s-WOx thin films were investigated to shed light on their performance as selective contacts, and their hole selectivity on Si were also characterized. It is found that there is a larger density of oxygen vacancies in s-V2Ox than s-WOx resulting in a larger amount of gap states, but their energy levels in s-V2Ox might not be favourable for carrier transport. We have measured a high work function of 5.17 eV for s-V2Ox and the Fermi level is located above the conduction band suggesting its n-type characteristic. On the other hand, the work function of s-WOx is only 4.71 eV and it is also a n-type semiconductor with the Fermi level situated below the conduction band. From the carrier lifetime studies, both materials are found to exhibit moderate passivation effect on Si and overall they can serve as good hole selective contacts for Si. The optimized power conversion efficiencies of planar s-V2Ox/Si and s-WOx/Si heterojunction solar cells are 10.8% and 9.3% respectively. To the best of our knowledge, the performance of the planar s-V2Ox/Si HSC is better than other reported result for planar configuration using solution process, and this is the first time that the performance of the planar s-WOx/Si HSC is reported.

We study the junction behavior of poly (3,4-ethylenedioxythiophene):polystyrenesulphonate/n-Si hybrid organic/inorganic heterojunction by reverse recovery transient (RRT) characterization. RRT response for PEDOT:PSS/n-Si hybrid junction is reported for various n-Si doping concentration and forward bias current injection level. The presence of settling time of 8.3–23.5 μs in the RRT response in contradiction to Schottky junction model commonly assumed for PEDOT:PSS/n-Si hybrid structure. The decrease in the minority carrier lifetime from 126.8 μs to 39.5 μs with increased n-Si doping concentration, suggests that minority carriers are stored at n-Si side of the junction, which is consistent with a p+-n junction model for the hybrid structure. The minority carrier lifetime is found to depend on forward bias current injection level, attributed to trap-saturation effect of the recombination-centers at the PEDOT:PSS/n-Si junction. The DC-IV characteristics of the PEDOT:PSS/n-Si hybrid junction are also consistent with the notion of diffusion and trap assisted recombination dominated dark current. The diffusion dominated transport of PEDOT:PSS/n-Si leads to an ideal p+-n junction behavior that leverages on the good transport properties of Si. Our findings are important in the modeling and optimization of the characteristics of electronic devices based on the organic/Si hybrid junction.

Development of Internet-of-Things requires the deployment of self-powered wireless sensor nodes (WSN). Towards this end, photovoltaic cells are often used to harvest ambient light energy. On the other hand, it is desirable to reduce the size of the WSN circuits as much as possible. However, WSN miniaturization will lead to less area available for solar cells and consequently, insufficient energy harvested to power the WSN. In this work, we develop a PV-Tower solar cell concept that offers a large active surface area for light absorption, while occupying only a small footprint. We demonstrate silicon-based PV-Tower solar cells with footprint areas of 0.2 mm2, 0.4 mm2, and 0.6 mm2, which can generate ≈80 times more power than conventional solar cells over the same footprint. We have also fabricated a small footprint PV-Tower module prototype that comprises 10 PV-Tower solar cells connected in series, which exhibits an open circuit voltage of 5.1 V. At the maximum power point, the module can deliver a voltage of 3.6 V and a power of ≈66.7 mW, which translates to an output power per footprint of ≈78.5 mW cm−2. By optimizing the module design, we estimate that there is room to significantly reduce its footprint and increase the output power per footprint by ≈10 times to 785 mW cm−2. The results show that the PV-Tower solar cell can serve as a compact small footprint photovoltaic energy harvesting device that can address the physical size constraints posed by miniaturization of the WSN circuit.

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O2 plasma etching of the polystyrene spheres, we managed to fabricate hexagonal nanostructured back reflectors. With the help of rigorous modeling, we study the parasitic losses in different back reflectors, non-active layers, and last but not least the light enhancement effect in the silicon absorber layer. Moreover, simulation results have been checked against experimental data. We have demonstrated hexagonal nanostructured amorphous silicon thin film solar cells with a power conversion efficiency of 7.7% and around 34.7% enhancement of the short-circuit current density, compared with planar amorphous silicon thin film solar cells. Published version

The compositional, optical and electrical properties of solution processed molybdenum oxide (s-MoO x ) film are characterized. The film has a composition of s-MoO$_{\mathbf {2.72}}$ with good transmittance above nearly 80%, a bandgap of 3.0 eV and low conductivity of 10$^{\mathbf {-6}}$ S/cm. S-MoO$_{\mathbf {x}}$/nc-Si heterojunction solar cells have been fabricated and the best device achieved a power conversion efficiency of 7.26%, open circuit voltage of 0.49 V, short circuit current of 29.92 mA/cm$^{\mathbf {2}}$, and fill factor of 49.07%.

We study the design of Si/organic hybrid (SOH) solar cells with interdigitated back contact (IBC) structure. SOH solar cells formed between n-Si and poly(3,4-ethylenedioxythiophene): polystyrenesulphonate (PEDOT:PSS) is a promising concept that combines the excellent electronic properties of Si with the solution-based processing advantage of an organic polymer. The IBC cell structure is employed to minimize parasitic absorption losses in the organic polymer, eliminate grid shadowing losses, and allow excellent passivation of the front Si surface in one step over a large area. The influence of Si thickness, doping concentration and contact geometry are simulated in this study to optimize the performance of the SOH-IBC solar cell. We found that a high power conversion efficiency of >20% can be achieved for optimized SOH-IBC cell based on a thin c-Si substrate of 40 μm thickness.

There is a great need for viable alternatives to today’s transparent conductive film using largely indium tin oxide. We report the fabrication of a new type of flexible transparent conductive film using silver nanowires (AgNW) and single-walled carbon nanotube (SWCNT) networks which are fully embedded in a UV curable resin substrate. The hybrid SWCNTs-AgNWs film is relatively flat so that the RMS roughness of the top surface of the film is 3 nm. Addition of SWCNTs networks make the film resistance uniform; without SWCNTs, sheet resistance of the surface composed of just AgNWs in resin varies from 20 Ω/sq to 107 Ω/sq. With addition of SWCNTs embedded in the resin, sheet resistance of the hybrid film is 29 ± 5 Ω/sq and uniform across the 47 mm diameter film discs; further, the optimized film has 85% transparency. Our lamination-transfer UV process doesn’t need solvent for sacrificial substrate removal and leads to good mechanical interlocking of the nano-material networks. Additionally, electrochemical study of the film for supercapacitors application showed an impressive 10 times higher current in cyclic voltammograms compared to the control without SWCNTs. Our fabrication method is simple, cost effective and enables the large-scale fabrication of flat and flexible transparent conductive films.

We have studied hole selective contacts molybdenum oxide (HyMoOx) fabricated based on solution process and the performance of HyMoOx/c-Si heterojunction solar cells. Characterization of the HyMoOx film revealed an amorphous structure with a low surface roughness of 1.27 nm, chemical composition of HyMoO2.72, high transmittance on glass of over 85%, bandgap of 3.0 eV and low conductivity of 10−6 S/cm. It also possesses a work function of ∼4.95 eV and good passivation effect on c-Si, as the Si surface recombination velocity is observed to reduce by a factor of 85 when passivated by HyMoOx film. The solution processed MoOx as a selective contact on silicon has a low saturation current J0 ∼ 150 fA/cm2 but with a high contact resistivity ∼5.6 Ωcm2. The fabricated HyMoOx/c-Si solar cell has the best power conversion efficiency (PCE) of 8.22%, open circuit voltage (Voc) of 463 mV, short circuit current density (Jsc) of 31.16 mA/cm2, and fill factor (FF) of 56.87%.

Surface photovoltage transients on solar junctions have often been associated with carrier lifetime in the literature. However, the carrier decay in a junction is not governed by a first order carrier decay, but resulting from a differential capacitance interacting with a differential conductivity. This phenomenon is well known as the Kane-Swanson formalism in an engineering context where the carrier density transient is measured by photoconductance with a microwave or infrared beam. In this work, we solve the same differential equations numerically to model the carrier decay in the large signal domain extending over five orders of carrier density. Since the surface voltage is linked to the carrier density by a logarithmic relation, we express the carrier decay as surface photovoltage transients. We show how from photovoltage transients, the same information as from photoconductance can be drawn. To demonstrate the method as a generic tool, it is applied to four types of solar cells, two monocrystalline silicon cells, a Perovskite solar cell, a transition metal oxide/silicon hybrid junction, and a CIGS solar cell. Acquiring photovoltage transients by Kelvin force microscopy allows working on partial junctions without top contact, speeding up research of future photovoltaic materials. Furthermore, parameters may be mapped with a better lateral resolution compared to microwave photoconductance. Accepted version

A simple two-step surface treatment process is proposed to boost the efficiency of silicon nanowire/PEDOT:PSS hybrid solar cells. The Si nanowires (SiNWs) are first subjected to a low temperature ozone treatment to form a surface sacrificial oxide, followed by a HF etching process to partially remove the oxide. TEM investigation demonstrates that a clean SiNW surface is achieved after the treatment, in contrast to untreated SiNWs that have Ag nanoparticles left on the surface from the metal-catalyzed etching process that is used to form the SiNWs. The cleaner SiNW surface achieved and the thin layer of residual SiO2 on the SiNWs have been found to improve the performance of the hybrid solar cells. Overall, the surface recombination of the hybrid SiNW solar cells is greatly suppressed, resulting in a remarkably improved open circuit voltage of 0.58 V. The power conversion efficiency has also increased from about 10% to 12.4%. The two-step surface treatment method is promising in enhancing the photovoltaic performance of the hybrid silicon solar cells, and can also be applied to other silicon nanostructure based solar cells. Accepted version