Crystalline silicon (c-Si) homojunction architectures like aluminum back-surface field (Al-BSF) and passivated emitter and rear cell (PERC) dominated the solar cell market for the last decades. Recently, carrier-selective passivating contact (CSPC) designs have shown that they can effectively reduce recombination losses and exhibit efficiencies above 25 % which approaches the Shockley-Queisser limit of single-junction solar cells. To overcome this intrinsic efficiency limit, research and industry have started to investigate multijunction devices which utilize two different absorber layers in order to reduce the spectral mismatch losses. In this project, the focus lies on the fabrication of a high temperature CSPC bottom cell with polycrystalline silicon oxide (poly-SiOx) for the application in a 2-terminal perovskite/c-Si tandem device. Poly-SiOx features a higher transparency due to a wider band gap which can decrease the free-carrier absorption (FCA) and induce larger band bending in comparison to the classic polycrystalline silicon (poly-Si) contacts. To fabricate a c-Si solar cell with high temperature carrier-selective passivating contacts, the passivation of the contacts was optimised using symmetric lifetime samples. It was found that the optimal processing conditions for the dry thermal oxidation process and the high temperature annealing step are 675 °C for 3 minutes and 900 °C for 15 minutes, respectively. This resulted in an implied open-circuit voltage (iVOC) for the n-doped and p-doped symmetric samples after hydrogenation of 745 mV and 674 mV, respectively. Those optimised processing conditions were adopted for the fabrication of a single-junction n-type front-side polished and p-type rear-side textured CSPC solar cell. This resulted in a solar cell with an efficiency of 16.67 %. By lowering the thermal budget of the recovery annealing conditions after the sputtering of the transparent conductive oxide (TCO), the passivation properties are restored more effectively. This resulted in an enhanced solar cell with a final efficiency of 18.76 %. Other techniques to improve the performance like the modification of the p-layer thickness, the incorporation of an additional annealing step after the a-Si deposition, or the introduction of indium tungsten oxide (IWO) as the TCO did not result in an improvement of the final solar cell efficiency. Optical simulations were performed in GenPro4 to investigate the optical performance of the solar cell. Finally, a 2-terminal perovskite/c-Si tandem device with a high temperature carrier-selective passivating c-Si bottom cell was fabricated in cooperation with TU Eindhoven. The final tandem solar cell exhibits an efficiency of 23.10 % with a fill factor of 74.00 %, a VOC of 1.76 V and a JSC of 17.81 mA/cm2.

Due to the high-efficiency potential over 40%, the two-terminal (2T) perovskite/c-Si tandem solar cell becomes a desirable and promising candidate for solar cells. The photovoltaic materials and devices (PVMD) group in TU Delft has developed the c-Si solar cell using poly-SiOx as carrier-selective passivating contacts. The utilization of poly-SiOx as carrier selective passivating contacts is relatively new and very interesting to be analyzed as its bandgap can be varied by changing its oxygen content. This can be used in the solar cell to increase the Jsc. In this work, the 2T perovskite/c-Si tandem solar cells' optimization has been conducted by means of optical and electrical simulations. Optical simulations of the 2T, 3T and 4T perovskite/c-Si tandem solar cells in GenPro4 are presented. The main objective is to show the new type of bottom cell's optical performance in the 2T, 3T, and 4T tandem solar cell. Furthermore, the two-terminal (2T) perovskite/c-Si tandem solar cell's electrical modeling framework with the new type of the bottom cell has been developed. In this model, the optical generation profile from GenPro4 was successfully imported into the semiconductor simulations software called Sentaurus TCAD. The perovskite and c-Si solar cells have been optimized separately. The perovskite solar cell optimization was conducted by changing parameters such as contact resistance, surface recombination velocity and thickness of each layer. This leads to the increase in the perovskite solar cell efficiency from 15.83% to 21.50%. This top cell was combined with a c-Si bottom cell with an efficiency of 25% to form a two-terminal (2T) tandem solar cell. The two-terminal (2T) perovskite/c-Si was further optimized by optimizing the tunnel recombination junction. The optimization of TRJ was done by varying the doping concentration of indium tin oxide (ITO) and spiro-OMeTAD, respectively. As a result, the 33.70% efficiency of the two-terminal (2T) perovskite/c-Si tandem solar cell was obtained.

Carrier selective passivating contacts (CSPC) have proven to effectively curtail the recombination losses emerging at directly metallised contacts of crystalline Silicon (c-Si) solar cells. CSPCs enabled using an ultra-thin interfacial tunnel oxide layer (SiOx) capped by a doped polycrystalline Silicon (poly-Si) layer also referred to as Tunnel Oxide Passivating Contacts (TOPCon) have resulted in efficiencies as high as 25.8%. This thesis project addresses the development of oxygen alloyed poly-Si (poly-SiOx) in combination with an interfacial oxide layer grown by dry thermal oxidation. The limited transparency of poly-Si based contacts brought on by high free carrier absorption (FCA) can be mitigated by the use of poly-SiOx based passivating contacts owing to their wider bandgaps which induce stronger band bending. To begin with, poly-SiOx CSPC were optimised by determining the optimum thermal budgets for tunnel oxide growth and hydrogenation scheme. Tunnel oxide layers grown at 675 ͦC 6 minutes demonstrated very good passivation for p-type polished and n-type textured CSPCs indicated by their implied Voc of 709 mV and 711 mV respectively. For the p-type textured CSPC identified as the primary limiting factor when deploying in c-Si solar cells, a tunnel oxide layer grown at 675 ͦC 3 minutes in conjunction with a two-step annealing scheme showed a crucial enhancement in passivation quality with a final implied Voc of 687 mV. The single side textured front back contacted (FBC) solar cell fabricated using the optimised p-type polished and n-type textured poly-SiOx CSPC recorded a conversion efficiency of 20.94% on a 4 cm2 screen printed solar cell. The reported efficiency is the maximum that has been attained so far for the configuration that uses a thermally grown tunnel oxide layer with poly-SiOx CSPCs. Effective carrier transport and carrier collection was illustrated by a fill factor (FF) of 79.6%. A Jsc of 37.91 mA/cm2 was recorded for the same. A comparison with a single side textured FBC solar cell that employed a tunnel oxide layer grown by nitric acid oxidation of Silicon (NAOS) revealed a superiority in performance by the thermally grown tunnel oxide layer resulting in better passivation and carrier selectivity. Lastly, the optimised n-type textured and p-type textured CSPCs were implemented on a double side textured FBC solar cell. The two-step annealing scheme that showed beneficial results for the p-type textured CSPC was implemented within the FBC solar cell, leading to an implied Voc of 698mV post hydrogenation. It is worth mentioning that this is the highest value achieved until now for this novel cell architecture. Implementation of screen printing resulted in a final conversion efficiency of 19.38% on a 4 cm2 solar cell with a FF and Jsc of 77.89% and 37.65 mA/cm2 respectively.

Performance of photovoltaic modules are widely expressed using their efficiency at Standard Test Conditions (STC). Although, real world conditions largely differ from this standard. Energy yield of photovoltaic modules at a certain location gives a clear indication of the performance of the module exposed to varying weather conditions. Photovoltaic Materials and Devices (PVMD) Toolbox developed at Delft University of Technology and implemented in MATLAB®, aims to simulate energy yield of photovoltaic modules while providing the flexibility of modifying cell-level to module-level parameters of the device. Accurately determining the irradiance falling on the module at a certain location and simulating the electrical properties of a solar cell at realistic conditions is crucial in determining the yield generated by a module. Due to the promising results displayed by the technology, in this study, energy yield of perovskite/c-Si tandem modules are simulated using newly developed daylight and parameter extraction models in PVMD toolbox. Due to high computational efficiency and functionality offered, Preetham daylight model is implemented as an improvement to Perez model currently used in PVMD toolbox. The model considers the effect of Rayleigh and Mie scattering, and turbidity of atmosphere in determining the distribution of diffuse irradiance across the skydome. By implementing the model, three factors can now be determined: luminance distribution, RGB co-ordinates and relative spectral power distribution over the skydome for any location. Luminance is calculated for every point in sky using Perez parametric function that use coefficients derived from simulated data for different sun directions and turbidity values. For all locations considered, Preetham model calculates higher luminance over the year by ~2%. Calculated luminance values normalized against zenith luminance is used to derive CIE xyY values and consecutively, the RGB co-ordinates that are rendered real-time to create images of the skydome for every hour in chosen timeframe. By calculating the relative spectral power distribution, analysis of incident light falling on the module from all points of the skydome is possible which especially deems useful for modelling tandem modules. To accurately simulate electrical properties of solar cell under varying operating conditions, parameter extraction model for simulated ASA J-V curves is implemented using an analytical method. For the c-Si and perovskite cells considered in the study, the reconstructed curves using extracted parameters fits ASA curve with RMSE or 1.98% and 3.02% respectively at STC. Using these models introduced in this study, energy yield of mono-facial and bi-facial 2T/4T tandem modules are calculated and analyzed for Rome, Reykjavik and Alice Springs. Depending on air mass of a location, perovskite thickness of mono-facial 2T tandem devices are optimized to produce maximum specific yield. All considered modules generate highest yield at Alice Springs due to high insolation at the location. The yield difference between modules while using the two daylight models is insignificant at <1%. With an increase in perovskite thickness, energy yield of 2T bi-facial modules increase significantly for high albedo while it drops beyond the optimum thickness due to current mismatch for low albedo. Bi-facial 4T module on high albedo (albedo= 0.85) surfaces show best performance out of all the modules producing 36% higher yield than mono-facial 4T module for Rome.

Tandem technology has emerged as one of the most promising innovations in the field of photovoltaics. Higher conversion efficiencies than standard single-junction cells have already been achieved. Proving how these laboratory conversion capabilities translate into real-world performance is therefore a main interest drive within the photovoltaic research community. Typically, photovoltaic device performance is assessed in Standard Test Conditions (STC). For the majority of climates, this is however not representative of actual operating conditions. With the aim of studying potential system applications, the energy yield prediction method adopted in this thesis analyzes tandem technology performance considering real-world conditions. For this scope, the PVMD Toolbox for PV system modeling is employed. The tandem device investigated in this work is a perovskite/c-Si based structure in a two-terminal architecture. In particular, a TU Delft own poly-SiOx based crystalline silicon bottom cell is utilized in the configuration. This structure is implemented in the Toolbox to carry out Optical simulations from cell to module system level. Operating conditions are introduced through use of the Toolbox Weather and Thermal models. These recreate real-world illumination and climate settings for the selected locations of Reykjavik, Rome and Alice Springs. With an STC-optimized perovskite thickness of 515 nm, the hourly implied photocurrent density of the device is calculated and validated. The jph annual average is 1.92, 3.34 and 5.01 mA/cm2 for the three locations, respectively. These values take into account a sub-cells current mis- match loss between 5 and 8% depending on location. To reproduce real-world cell electrical parameters behavior, the variable irradiance and temperature sub-cells J-V curves have been obtained. A poly-SiOx based silicon prototype was tested in laboratory settings and its curves then utilized in simulations after measurements validation. The module annual energy yield is computed through simulations with the Toolbox Electric model. In terms of specific DC yield, the STC-optimized module delivers 820, 1,427 and 2,161 kWh/kWp/year in the three locations. The power mismatch lowering effect due to the fill factor gain compensates the current mismatch in this 2T configuration, reducing energy mismatch losses. This performance is then compared to a reference single-junction poly-SiOx based silicon module, to show how tandem technology potentially outperforms standard modules differently depending on climatic conditions. The tandem module is also assessed in terms of DC performance ratio (PR), exhibiting values over 0.94 for all three locations. The structure is then real-world optimized by varying perovskite thickness, with the goal of maximizing location-specific energy yield and PR. Slight improvements are obtained for the Reykjavik and Alice Springs locations, where the energy yield increases by few relative percentage points along with PR.