J.A. Andrade-Arvizu

SnS-based thin film solar cells: perspectives over the last 25 years

New types of thin film solar cells made from earth-abundant, non-toxic materials and with adequate physical properties such as band-gap energy, large absorption coefficient and p-type conductivity are needed in order to replace the current technology based on CuInGaSe2 and CdTe absorber materials, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). The constituent elements of the SnS film are abundant in the earth’s crust, and non-toxic. If this compound is used as the absorber layer in solar cells, high efficient devices should be fabricated with relative low cost technologies. Despite these properties, low efficiency SnS-based solar cells have been reported up to now. In this work, we present a review about the state of the art of SnS films and devices. Finally, an analysis about different factors that are limiting high efficiency solar cells is presented.

Towards a CdS/Cu2ZnSnS4 solar cell efficiency improvement: A theoretical approach

In this work, a device model for Cu2ZnSnS4 (CZTS) solar cell with certified world record efficiency is presented. A study of the most important loss mechanisms and its effect on solar cell performance was carried out. The trap-assisted tunneling and CdS/CZTS interface recombination are introduced as the most important loss mechanisms. Detailed comparison of the simulation results to the measured device parameters shows that our model is able to reproduce the experimental observations (quantum efficiency, efficiency, Jsc, FF, and Voc) reported under normal operating conditions. Finally, a discussion about a further solar cell efficiency improvement is addressed.

Route towards low cost-high efficiency second generation solar cells: current status and perspectives

The most efficient thin film solar cells are based on Cu(In,Ga)(S,Se)2 (CIGSSe) and CdTe compounds, known as second generation polycrystalline thin films. The challenge of these materials is to reduce the cost per watt of solar energy conversion, but they are actually formed by expensive and/or scanty elements in the earth’s crust such as In, Ga, Te and other that present toxicity issues like Cd. In the last years, new materials with properties of interest for photovoltaic applications and formed by non toxic and relatively abundant elements, have been suggested as alternatives to the main second generation solar cells based on CdTe and CIGSSe. Semiconductor compounds with kesterite structure (Cu2ZnSn(SxSe1−x)4, Cu2ZnSnS4, Cu2ZnSnSe4) and other like In2S3, all of them Cadmium-free have been proposed as new candidates for thin film solar cells. However, reported solar cell efficiencies for these compounds have not yet reached the expected values. In this work, we present a review of the limiting factors for achieving high efficiency in thin film solar cells, related to deposition methods as well as the different mechanisms that limit cell performance. Significant results in the processing of solar cells using some of these compounds and preliminary results of the In2S3 deposition with an overview to its use as buffer layer are presented.

The role of buffer/kesterite interface recombination and minority carrier lifetime on kesterite thin film solar cells

This paper presents for the first time a theoretical study of the impact of kesterite/buffer interface recombination and kesterite minority carrier lifetime on both CZTS and CZTSe solar cells. It demonstrates that only an 11% efficiency can be reached in CZTS solar cells by improving absorber crystalline quality, pointing out the need for an improved CdS/CZTS interface. It further demonstrates that a CZTS solar cell efficiency enhancement of up to 18%, with an open-circuit voltage value of up to 918 mV, can be achieved depending on CZTS minority carrier lifetime and CdS/CZTS interface recombination speed values. Moreover, this paper shows that by improving CZTSe crystalline quality, a record efficiency value of 17% could be achieved without focusing on improving CdS/CZTSe interface quality. Consequently, CZTSe is presented as a better candidate for solar cell applications. Conditions under which CdS/kesterite interface recombination and trap-assisted tunneling recombination become dominant are provided. In particular, we find that CdS/CZTS interface recombination is the dominant transport mechanism for CZTS minority carrier lifetime values higher than 5 ns, while for CZTSe minority carrier lifetime values lower than 0.1 μs, CdS/CZTSe interface losses are negligible.

Study of CBD-CdS/CZTGSe solar cells using different Cd sources: behavior of devices as a MIS structure

CdS buffer layer plays an important role in thin film solar cells; as a result, a deep understanding of its physical properties and impact on solar cell performance is highly required. In this work, we report results on growth conditions of CdS thin films deposited by chemical bath method to be used as insulators in MIS structure instead of the traditionally assumed p–n junction. Three different Cd sources—CdCl2, Cd(NO3)2, and CdSO4—are considered for CdS processing. The impact of Cd source on CdS physical properties as well as on the electro-optical device properties of CdS/CZTGSe solar cells is evaluated. Furthermore, interface state properties are calculated as a function of temperature. These states are a result of the CdS interaction with both the TCO and Kesterites, depending on the Cd source used in solution of the chemical bath deposition. Besides, some important requirements to be considered in order to improve device efficiency are discussed in the present work.

Assisted laser ablation: silver/gold nanostructures coated with silica

The synthesis processes of metallic nanoparticles have seen a growing interest in recent years, mainly by the potential applications of the phenomenon of localized surface plasmon resonance associated with metallic nanoparticles. This paper shows a fast method to synthesize silver, gold and silver/gold alloy nanoparticles coated with a porous silica shell by the assisted laser ablation method in three steps. The method involves a redox chemical reaction where the reducing agent is supplied in nanometric form by laser ablation. In the first step, a silicon target immersed in water is ablated for several minutes. Later, AgNO3 and HAuCl4 aliquots are added to the solution. The redox reaction between the silver and gold ions and products resulting from ablation process can produce silver, gold or silver/gold alloy nanoparticles coated with a porous silica shell. The influence of the laser pulse energy, ablation time, Ag+ and Au3+ concentration, as well as the Ag+/Au3+ ratio, on optical and structural properties of the nanostructures was investigated. This work represents a step forward in the study of reaction mechanisms that take place during the synthesis of nanoscale materials by the assisted laser ablation technique.

Towards a CdS/Cu 2 ZnSnS 4 solar cell efficiency improvement

In this work, a device model for Cu2ZnSnS4 (CZTS) solar cell with certified world record efficiency is presented. A study of the most important loss mechanisms and its effect on solar cell performance was carried out. The trap-assisted tunneling and CdS/CZTS interface recombination are introduced as the most important loss mechanisms. Detailed comparison of the simulation results to the measured device parameters shows that our model is able to reproduce the experimental observations (quantum efficiency, efficiency, Jsc, FF, and Voc) reported under normal operating conditions. Finally, a discussion about a further solar cell efficiency improvement is addressed.