## 1 Introduction  
To achieve carbon neutrality by replacing or absorbing emissions in response to global warming, there is growing interest in solar power generation [1, 2, 3, 4, 5]. Solar power generation is a method of producing electricity from solar panels using sunlight. It does not require fuel because it produces electricity from the sun and does not emit harmful substances into the atmosphere during the generation process [6, 7]. Additionally, solar power generation is nearly silent during the electricity generation process and has minimal impact on the surrounding environment during construction, making it increasingly popular as an environmentally friendly energy source [8, 9, 10]. Recently, the importance of BIPV power generation significantly increased due to various demands on energy usage in densely populated areas with buildings [11, 12]. BIPV integrates a solar power generation system into the architectural exterior elements of a building to allow the building itself to produce electricity [13, 14, 15]. It can be installed in various locations, such as windows, exterior walls, roofs, and more, and is like a building material that can generate its own electricity rather than a separate solar power facility. Because BIPV does not require a separate site, it can be harmoniously integrated into the design of buildings, which makes it easy for residents to accept. By integrating solar modules into buildings, BIPV enables buildings to generate their own electricity, reducing their reliance on grid power, which can lead to energy offsets and contribute to reducing electricity peaks during high and low seasons [16, 17, 18]. This environmentally friendly solar energy technology can increase the added value of buildings and can be applied to both new construction and existing building renovations [19, 20].  
However, there are obstacles to the adoption of BIPV, such as high initial installation cost, technical complexity, sustainability of the market and economic feasibility. Especially, since BIPV modules are installed on a limited area of the building, the power generation capacity is relatively low, which ultimately results in low efficiency compared with initial cost [21; 22; 23]. The shingled technology was proposed to address these issues by connecting cells with electrically conductive adhesives (ECA) to increase cell density and consequently enhance module output [24]. However, the impact of the spacing between shingled strings on output variation has not been thoroughly studied. Understanding the key factors for maximizing the development efficiency of building-integrated photovoltaics (BIPV) is crucial. so, it is important to understand the key factor for maximizing power generation of BIPV. In this study, the performance enhancement of a BIPV module was studied through the optical coupling effect of the shingled PV module using PSpice simulation. To verify simulation results, BIPV modules were fabricated by using four shingled strings, with each string made up of 17 interconnected divided cells were large enough to allow an analysis of the changes in factors. For the comparative analysis based on spacing between strings, modules were fabricated with string spacing of 0.2 cm, 0.5 cm, 1 cm, 2 cm, and 4 cm, and the coupling effect under each condition was analyzed. In addition, the coupling effect on the module performance according to the reflection of light was studied by analyzing the optical coupling effect based on the different interlayers of the module.