Thin Film Deposition Technologies and Application in Photovoltaics

*Ning Song and Shuo Deng*

### **Abstract**

Renewable energy will play a critical role in reducing emissions to mitigate climate change. Photovoltaic (PV) is one of the most promising and prominent techniques for electricity generation based on renewable solar energy. Thin films play a critical role in PV in Si and thin film solar cells and solar modules. They can be used as an absorber layer, buffer layer, hole/electron transportation layer, passivation layer, transparent conductive oxide and antireflection coating on solar cells or solar modules. This chapter provides an overview of thin film deposition techniques and applications in photovoltaics and highlights techniques that are currently in use or are promising for mass production.

**Keywords:** photovoltaic, thin films, Si solar cell, thin films solar cells, solar modules

### **1. Introduction**

In the past two decades, human-induced climate change has increased the frequency and intensity of weather and climate extremes around the globe and has cost countries hundreds of billions of dollars and thousands of lives [1]. The world is facing an energy crisis, and the prices of fossil fuels keep increasing, affecting every household. From personal, national and global perspectives, carbon neutrality is necessary. Renewable energy is a predominant term in carbon-neutral roadmaps for every country, and solar photovoltaics (PV) is currently the most affordable, accessible and prevalent technology. It involves the generation of electricity from sunlight shining through the front cover onto solar cells packaged into a solar module.

As of May 2022, global PV installations have reached 1 TW. In the PV market, crystalline-Si (c-Si) solar cells account for 95% and thin film solar cells account for 5% [2]. Thin films (<1um) have an important role in Si solar cells, thin film solar cells and solar modules as absorber, passivation, buffer, electron/hole transport and antireflection coating (ARC) layers on solar cells and modules. Thin films can range from single crystal to amorphous, fully dense to less than fully dense, pure to impure and thin to thick [3].

Any new technology adapted to PV would be suitable for mass production at a reasonable cost. Meanwhile, the industry is shaping itself in the direction of higher conversion efficiency and lower cost, hence new materials and technologies are always under investigation for companies to keep their products competitive.

Therefore, it is significant to evaluate the scalability and cost-effectiveness of fabrication technologies.

The following benefits of thin films make them naturally attractive for the industry [3]:


In materials science, thin film technologies can be divided into gaseous state, solution state and molten or semi-molten state, where gaseous and solution states produce films with a thickness level of nanometers (nm) and Angstroms (Å), which are at the desired level of controllability for photovoltaics. Considering the accessibility and cost, the main thin film deposition techniques used in photovoltaics are physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical solution deposition and sol–gel [3].
