With the aim of achieving high efficiency, cost-effectiveness, and reliability of solar cells, several technologies have been studied. Recently, emerging materials have appeared to replace Si-based cells, seeking economic fabrication of solar cells. Thin-film solar cells (TFSCs) are considered strong candidates for this mission, specifically perovskite-based solar cells, reporting competitive power convergence efficiencies reaching up to 25.7%. Substantial efforts have been invested in experimental and research work to surpass the Si-based cells performance. Simulation analysis is a major tool in achieving this target by detecting design problems and providing possible solutions. Usually, a TFSC adopts p-i-n heterojunction architecture by employing carrier transport materials along with the absorber material in order to extract the photogenerated electrons and holes by realizing a built-in electric field. Eventually, this dependency of conventional heterojunction TFSCs on carrier transport layers results in cost-ineffective cells and increases the possibility of device instability and interface problems. Thus, the design of p-n homojunction TFSCs is highly desirable as an essential direction of structural innovation to realize efficient solar cell operation. In this review, a summary of the fundamentals of TFSC materials, recent design and technology progress, and methodologies for improving the device performance using experimental research studies will be discussed. Further, simulation analysis will be provided by demonstrating the latest research work outcomes, highlighting the major achievements and the most common challenges facing thin film homojunction solar cell structures and the methods to improve them.

Double-junction solar devices featuring wide-bandgap and narrow-bandgap sub-cells are capable of boosting performance and efficiency compared to single-junction photovoltaic (PV) technologies. To achieve the best performance of a double-junction device, careful selection and optimization of each sub-cell is crucial. This work presents the investigation of an all-thin-film two-terminal (2T) monolithic homojunction perovskite (PVK)/c-Si tandem cell using Silvaco TCAD simulation. The front sub-cell utilizes homojunction PVK that has a bandgap of 1.72 eV, whereas the rear sub-cell uses thin c-Si with a bandgap of 1.12 eV. Both cells are connected via a p⁺⁺/n⁺⁺ silicon tunnel diode. Experimental calibration of the heterojunction PVK and c-Si cells yields power conversion efficiencies (PCE) of 18.106% and 17.416%, respectively. When integrated into an initial PVK/c-Si tandem, the resulting cell achieves a PCE of 29.38%. To compare the performance, the heterojunction PVK layer is replaced with an n-p homojunction PVK layer, revealing the impact of the absence of a surplus built-in electric field in the perovskite film as a strong limiting factor. Further, a thorough investigation of four distinct structures for the n-p homojunction PVK cell is conducted. The four structures include a complete cell, electron transport layer (ETL)-free, hole transport layer (HTL)-free, and carrier transport layer (CTL)-free structures. The results show that the CTL-free structure has significant potential after applying certain optimization techniques that result in reducing surface recombination, enhancing the built-in electric field, and improving light absorption. With the current-matching condition achieved, the tandem efficiency reaches 36.37%.

Current mismatch due to solar cell failure or partial shading of solar panels may cause a reverse biasing of solar cells inside a photovoltaic (PV) module. The reverse-biased cells consume power instead of generating it, resulting in hot spots. To protect the solar cell against the reverse current, we introduce a novel design of a self-protected thin-film crystalline silicon (c-Si) solar cell using TCAD simulation. The proposed device achieves two distinct functions where it acts as a regular solar cell at forward bias while it performs as a backward diode upon reverse biasing. The ON-state voltage (V_ON) of the backward equivalent diode is found to be 0.062 V, which is lower than the value for the Schottky diode usually used as a protective element in a string of solar cells. Furthermore, enhancement techniques to improve the electrical and optical characteristics of the self-protected device are investigated. The proposed solar cell is enhanced by optimizing different design parameters, such as the doping concentration and the layers’ thicknesses. The enhanced cell structure shows an improvement in the short-circuit current density (J_SC) and the open-circuit voltage (V_OC), and thus an increased power conversion efficiency (PCE) while the V_ON is increased due to an increase of the J_SC. Moreover, the simulation results depict that, by the introduction of an antireflection coating (ARC) layer, the external quantum efficiency (EQE) is enhanced and the PCE is boosted to 22.43%. Although the inclusion of ARC results in increasing V_ON, it is still lower than the value of V_ON for the Schottky diode encountered in current protection technology.