Individual actions cannot solve the current climate crisis. Part of the collective effort is to research solar energy as new ways to produce cleaner, cheaper and more efficient electricity. Among all the current solar cell technologies, a thriving and promising one is perovskite as an absorber material. In the last ten years, the power conversion efficiency evolved with a steep rhythm. In 2019, a maximum of 25.2% in a single junction configuration was reported, while more actual research proves that using them as a tandem can reach up to 30%. Perovskites have the advantage of changing their bandgap by ion-­mixing, from as low as 1.2 eV to even higher than 2.5 eV. Besides, it is flexible, translucent and has similar efficiencies to c­-Si; while being cheaper and easier to produce. It is expected that it will replace c­-Si-­based solar cells in the long run and significantly reduce the price of solar energy. This project is developed under the Photovoltaic Materials and Devices (PVMD) section of TU Delft, in conjunction with HyET Solar and Flamingo PV. The software ASA and GenPro4 were used to validate single-­junction solar cells and optimize tandem devices. The goal of this thesis is aligned to HyET’s ob­jective: improve its flexible thin-­film solar cell by increasing the power conversion efficiency above 12%. To carry out the validation and calibration of the single­-junction references, first, a study of all the possible perovskite­-based solar cells was performed. The chosen perovskites have a Methylamonium and Formamidinium combination. The first one has a bandgap of 1.55 eV and works as a high bandgap absorber material (K0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3), while the low bandgap corresponds to 1.25 eV ((FASnI3)0.6(MAPbI3)0.4) [20]. By adjusting some of the absorber layers’ electrical parame­ters, the references’ electrical properties were matched. Once validated, the respective p­i­n junctions of the perovskite solar cells were introduced into HyET’s solar cell architecture. By doing this, it is already possible to see the advantages of using per­ovskites as absorber materials: the power conversion efficiency grew from 7.71% to 18% and 19.45% for the high and low bandgap cells. Besides, there is also a better use of the light spectrum. Cali­brating a tandem solar cell is much more complicated. That is why it is done first on the individual single-­junction solar cells, and afterwards, both are stacked together. The first step to optimize a tandem device is to do an optical simulation (GenPro4). By analyzing the absorptance of the tandem device and the optical current of the top and bottom absorber materials, it is possible to obtain the best combination for the current matching of the tandem solar cell. By modifying both of the absorber materials’ thicknesses, the optical current mismatch can be reduced. As a result: 300 nm and 600 nm thickness for the a­-Si / LBG perovskite tandem, and 120 nm and 1700 nm for the HBG perovskite / nc-­Si; achieving a mismatch below 0.04 mA/cm2 and 0.2 mA/cm2 correspondingly. The second step in optimizing a tandem device involves an electrical simulation (ASA). The optimization is related to facilitating tunneling recombination at the n­-p junction by adjusting the doping of these layers. The optimized tandem solar cells have the following electrical properties: 1.56 V, 14.54 mA/cm2, 0.85 and 19.69% for fill factor and PCE for the HBG perovskite / nc-­Si tandem solar cell; while 1.55 V, 11.13 mA/cm2, 0.72 and 12.36% for fill factor and PCE of the other. With these results, it is plausible to confirm that HyET’s objective of having thin-­film flexible solar cells with a PCE above 12% can be met by using perovskite technology in their production line.

Emerging PV technologies like Perovskite has lead to the development of Perovskite/Silicon (Pvk/c-Si) tandem device (Multi-junction device) and has now gained a lot of momentum and attention due to the fact that the tandem device can reach a Shockley-Quisser limit of about 44.1% efficiency. But to speed up its development, a lot of emphasis is made on conducting tandem solar cell device simulations to have get a good idea on the experiments that can be carried out. Solar cell simulations for tandem devices are carried out in advanced 2D/3D solar cell simulators like SETFOS or Synopsys TCAD Sentaurus. These softwares have large computational time and have complex user interface making simulations challenging. There are 1D solar cell simulators like ASA (Advanced Semiconductor Analysis) developed at TU Delft that has less computational time with an easy and intuitive interface. But ASA does not have the appropriate tunnelling models to simulate the tunnel recombination junction characteristics of perovskite silicon tandem devices. To make ASA a complete software suite for simulating perovskite silicon tandem device, tunnelling models proposed by Ieong et al. is used for both direct and band to band tunnelling. These tunnelling models use basic inputs like band energy data, electrostatic potential data and electric field data for a particular device and outputs the tunnelling generation rate that can simply be added to the continuity equations for electrons or holes during the simulation of the device. A fully fledged algorithm was designed for the automation of the direct tunnelling and the band to band tunnelling process with limited input from the user while using the models proposed by Ieong et al. In simple terms, the algorithm takes in the required input and scans through the device for every interface to check for tunnel contributions and performs calculations when necessary. All necessary conditions are included inside the algorithms to ensure that the simulation is accurately solved. The validation of the newly developed tunnelling algorithm was commenced for PN junction, Silicon hetero-junction and finally the Perovskite-Silicon tandem device. The JV curve for the above device simulations with and without incorporated tunnelling models was extracted and a comparison was made with literature results and simulation results from other software suites. The newly developed tunnelling algorithms was concluded to be accurate. The JV curve obtained from the ASA simulation showed good agreement with literature results and simulation results from other software suites with error percentages of less than 3% for open circuit voltage, short circuit current and fill factor. With proper tuning of the device layer thickness, texturing on multiple layers for the tandem device and enhancing the mobility of the non-absorber layers for the perovskite top cell, further improvement can be expected in the simulation. These methods can eventually lead to reaching the Shockley Quisser limit of about 35.7% efficiency for the perovskite silicon tandem solar cell even when general opto-electrical losses are taken into account.