The global demand for sustainable and lightweight energy technologies continues to drive the development of advanced thin-film solar cells. Their potential for reduced material consumption, flexible integration, and scalable manufacturing makes them an essential component in the future of photovoltaics. However, despite decades of progress, thin-film silicon devices remain limited by material disorder and stability constraints, motivating the search for improved absorber and interface materials.

This research focuses on developing a predictive optical–electrical simulation framework for thin-film solar cells, capable of replicating real-world device behavior and guiding the design of next-generation architectures. The framework couples optical ray-tracing in GenPro4 with two-dimensional carrier-transport modeling in Sentaurus TCAD, allowing a realistic representation of textured interfaces, multilayer stacks, and lateral transport effects. The study begins with the calibration of single-junction amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) p–i–n cells against experimental data. These validated models are then combined into a tandem a-Si:H/nc-Si:H configuration, forming the optical and electrical foundation for further analysis.

Building on this baseline, the framework is extended to investigate flexible and hybrid device concepts. The transition from the rigid Asahi U-type glass substrate to a flexible configuration demonstrated the feasibility of lightweight devices, though efficiencies remained limited to approximately 10\% due to defect-assisted recombination and weak near-infrared absorption. To overcome these limitations, perovskite absorbers were explored. Single-junction perovskite devices with various hole-transport layers (HTLs) achieved simulated efficiencies up to 22%, with NiOx and nc-SiOx providing superior thermal and chemical stability. A hybrid a-Si:H/perovskite tandem reached 16% efficiency, benefiting from the protective silicon top layer but constrained by its lower current. A fully perovskite–perovskite (PVK/PVK) tandem employing inorganic and nc-SiOx HTLs achieved simulated efficiencies of 29%.

Finally, a detailed fill factor (FF) compensation study was conducted to quantify how current mismatch, recombination mechanisms, and electric-field distribution affect tandem performance. Five targeted case studies established design rules for stabilized operation through controlled mismatch, bandgap tuning, and optical optimization for a a-Si:H/nc-Si:H tandem solar cell.

Overall, this work delivers a unified simulation-based framework for the design and optimization of thin-film and hybrid tandem solar cells. The results provide fundamental insight into the performance limits of silicon and perovskite tandems and outline practical routes toward high-efficiency, lightweight, and manufacturable photovoltaic technologies. ... Read more

Photovoltaic solar energy is one of the most powerful renewable sources, playing a key role in transitioning the global energy sector from fossil fuels to zero-carbon emissions. The second generation of photovoltaic technology, such as thin-film silicon-based devices, offers potential for significant performance improvements. Among the layers that can be optimized, the front contact, composed of transparent conductive oxide (TCO) materials, is crucial. As the first layer to encounter incident light, TCO has to meet the high transparency requirement. Additionally, it has to offer high conductivity to transport carriers from the absorber layers to the metal contact. However, there is a trade-off between transparency and conductivity—improving one often compromises the other. Instead of seeking a single layer that balances these properties, an alternative approach involves the use of bilayers. Bilayers consist of two TCOs: one optimized for transparency and the other for conductivity. This thesis study focus on the design of bilayer configurations using two distinct materials, one optimized for transparency and the other for conductivity. Those designs aim to overcome the limitations of single-layer TCOs and achieve superior performance. Indium Cerium Oxide (ICO) and Hydrogenated Indium Oxide (IOH) were selected as conductive materials due to their excellent electrical properties, while intrinsic Zinc Oxide (i-ZnO), known for its high transparency, was used as the transparent layer. Tin Oxide (SnOx), a promising alternative, was also explored and integrated into bilayer configurations. All depositions were performed using Radio Frequency magnetron sputtering. The design process began by optimizing deposition conditions for each material. For ICO, power and process pressure were the examined variables, while for IOH, power and partial water pressure were studied. For SnOx, power and gas composition during deposition were evaluated. After determining the optimal deposition parameters based on opto-electrical properties examination, the following bilayer combinations were produced: IOH/i-ZnO, ICO/i-ZnO, and IOH/SnOx. In these bilayer depositions, the conductive material (IOH or ICO) was deposited first, followed by the transparent layer (i-ZnO or SnOx). The bilayer configurations exhibited superior opto-electrical properties compared to single layers. Specifically, the bilayers maintained high transparency with carrier densities of 1-2×1019 cm−3, minimizing parasitic absorption in the near-infrared region of the solar spectrum. Mobility values of 50-60 cm2/Vs ensured excellent lateral conductivity. These results demonstrated that bilayers preserve the best attribute of each composed material and the combination is a superior option for silicon-based solar cells. The initial depositions were conducted on flat glass substrates. Since silicon-based solar cells use textured substrates, the same bilayer configurations were also deposited on textured surfaces. The results showed that mobility values remained consistent at 50-60 cm2/Vs, though free carrier density was increased to 7-9×1019 cm−3 . However, those bilayers still outperformed single layers, and with further optimization, the issue of reduced free carrier density can be addressed. ... Read more

Thin film solar cells are devices that make use of thin layers to generate electricity from solar energy. Among various layers present in a thin film solar cell architecture, transparent conductive oxide (TCO) is crucial. TCOs are a set of materials with a unique set of properties. As a front contact, TCOs are required to offer high transparency to allow photons to reach the absorber layer to generate charge carriers. At the same time, TCOs need to be conductive as well to transport charge carriers from absorber to the metal electrode. However, there exists a trade-off where improvement to one property often comprises the other.
The concept of a bi-layer TCO configuration is explored in this project which makes use of two single layer TCOs: one with superior electrical properties and the other with superior optical properties. Hydrogenated indium oxide (IOH) is investigated as the conductive layer while the intrinsic zinc oxide (i-ZnO) as the transparent layer. Various other conductive layers are also tried in combination with i-ZnO, those being - Cerium doped indium oxide (ICO) and Cerium and hydrogen co-doped indium oxide (ICOH).
The first step to produce highly conductive bi-layer films is optimise post-deposition annealing parameters. Emphasis is placed on optimising annealing time, which tracing out the behavior of change in opto-electrical properties of the bi-layer after every 10 min increment in annealing time. 140 minutes is found as the optimum annealing time for IOH/i-ZnO bi-layers on both flat glass and textured glass substrates.
Novel highly conductive IOH/i-ZnO bi-layer were deposited demonstrating mobility of 143 𝑐𝑚^2/𝑉 𝑠 and carrier concentration of 1.05𝑥10^19 𝑐𝑚^−3 on flat glass. The bi-layer has the ability to not only retain individual constituent TCO properties and also to surpass the limitations of their individual TCOs. This attributes to the fact that the free charge carriers transport takes place a t the interface between TCO layer in the bi-layer stack. The ICO/i-ZnO and ICOH/i-ZnO structures were deposited, both bi-layers demonstrated mobility below 100 𝑐𝑚^2/𝑉 𝑠, however they outperformed their layers both electrically and optically.
IOH/i-ZnO bi-layer construction was also deposited on textured glass substrates. Best sample demonstrates mobility as high as 110 𝑐𝑚^2/𝑉 𝑠 with a carrier concentration of 3.63𝑥10^19 𝑐𝑚^−3. The reason for slightly lower mobilities is attributed to the inconsistency in shape and size of the textures present on the substrate, which leads to non-uniform deposition of IOH across the entire surface. Further investigation will lead to understanding hydrogen’s role in the IOH/i-ZnO bi-layer and the extent to which bi-layer performance on textured substrates can be improved. ... Read more

To make silicon thin film solar cells attractive to the market, their efficiencies should reach the efficiencies of the dominant crystalline silicon solar cell. Therefore the search for ways to improve the efficiency of silicon thin film solar cells continues. TCO front contact layers and back reflector layers play a significant role in the increase of thin film solar cell efficiencies. For the optical characterization of these TCO layers, commonly used methods are found to differ significantly in results regarding the extinction coefficient which makes their accuracy questionable.

This research consists of two main parts. For the first part, the commonly used optical characterization methods spectroscopic ellipsometry and spectrophotometry + data analysis in SCOUT are analyzed in accuracy and compared to newly introduced methods using spectrophotometry + data analysis in GenPro4 and photothermal deflection spectroscopy + data analysis in GenPro4 to build a guide on optical characterization of TCO materials. For the second part, the optical response determined using the software GenPro4 of a double junction silicon thin film solar cell for a novel bi-layer front contact design consisting of IOH and i-ZnO will be compared to the optical response for standard used AZO, and ITO single layers to find the best front contact design. Furthermore, the optical response of a double junction silicon thin film solar cell for a back reflector containing an i-ZnO layer on top of the silver back contact will be compared to the optical response for a back reflector containing an AZO layer on top of the silver back contact to find the best back reflector design.

From the results of the optical characterization methods, it is concluded that photothermal deflection spectroscopy + data analysis in GenPro4 is the most accurate method for determining the extinction coefficient of a TCO material. The results of the optical simulations for front contact TCO and back reflector TCO designs showed that the bi-layer can enhance the optical response of a double junction silicon thin film solar cell significantly compared to the AZO and ITO single layers. The i-ZnO TCO back reflector layer was found to induce less parasitic absorption and therefore a better optical response of the double junction silicon thin film solar cell. ... Read more

The journey towards increasing thin film solar cell efficiency is a continuously ongoing one, where each layer in the cell adds its own contributions and limitations. The transparent conductive oxide (TCO) is the first layer to encounter incident light on these cells and therefore needs to fulfil the requirement of high transparency. Carriers generated in the absorber layers of a thin film solar cell are transported to a metal electrode through the TCO, laying a conductivity requirement as well. A trade-off exists between transparency and conductivity, where one cannot be enhanced without sacrificing the other.
Indium tin oxide (ITO) currently delivers the best trade off, thus is the most commonly applied TCO.

In this thesis study, candidate TCO materials were deposited and analysed in order to surpass the opto-electrical properties of ITO. In addition to depositing ITO, hydrogen doped indium oxide (IOH) and intrinsic zinc oxide (i-ZnO) thin films were deposited using RF magnetron sputtering. Substrate temperature, RF power, deposition time and H2O partial pressure (only for IOH) were the varied parameters during depositions. IOH was found to surpass ITO in terms of conductivity, while i-ZnO surpassed ITO in terms of transparency. The best performing IOH and i-ZnO samples with regard to their respective superior parameters were chosen to be combined.

A TCO bi-layer was constructed by stacking a i-ZnO layer on top of a IOH layer. The IOH layer ensures good lateral conductivity, while the i-ZnO layer secures minimized parasitic absorption in the near infrared region. After being subjected to post deposition annealing, the bi-layer displayed opto-electrical properties superior to that of the individual i-ZnO and IOH layers. The highest electron mobility achieved for the bi-layer was 103,70 cm^2 /Vs with a carrier density of 0,3*1020 carriers/cm^3. The working principle is the capping effect which i-ZnO has on IOH, keeping hydrogen contained within the bilayer during annealing. Further investigation will lead to additional information on the behaviour of hydrogen within the as deposited bi-layer in comparison to the annealed
one. ... Read more