Brief introduction

    Thin-film solar cells are a type of solar cell made by depositing thin layers of photovoltaic material onto a glass, plastic or metal substrate. Thin-film solar cells are typically much thinner than the wafers used in conventional crystalline silicon based solar cells. Thin-film solar cells are commercially made with one of several materials including cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon (a-Si, TF-Si).

    Solar cells are often classified into generations based on the kinds of light-absorbing layers used to make them. The most well-established or first-generation solar cells are made of single- or multi-crystalline silicon. This is the dominant technology currently used in most solar PV systems. Most types of thin-film solar cells are classified as second generation, made using thin layers of materials like amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium gallium selenide (CIGS), or gallium arsenide (GaAs). Solar cells made with newer, less established materials are classified as third-generation or emerging solar cells. This includes some innovative thin-film technologies, such as perovskite, dye-sensitized, quantum dot, organic, and CZTS thin-film solar cells.

    Thin-film cells have several advantages over first-generation silicon solar cells, including being lighter and more flexible due to their thin construction. This makes them suitable for use in building-integrated photovoltaics and as semi-transparent photovoltaic glazing material that can be laminated onto windows. Other commercial applications use rigid thin film solar panels (interleaved between two panes of glass) in some of the world's largest photovoltaic power stations. Additionally, the materials used in thin-film solar cells are typically produced using simple and scalable methods more cost-effective than first-generation cells, leading to lower environmental impacts like greenhouse gas (GHG) emissions in many cases. Thin-film cells also typically outperform renewable and non-renewable sources for electricity generation in terms of human toxicity and heavy-metal emissions.

    Despite initial challenges with efficient light conversion, especially among third-generation PV materials, as of 2023 some thin-film solar cells have reached efficiencies of up to 29.1% for single-junction thin-film GaAs cells, exceeding the maximum of 26.1% efficiency for standard single-junction first-generation solar cells. Multi-junction concentrator cells incorporating thin-film technologies have reached efficiencies of up to 47.6% as of 2023.

    Many thin-film technologies have been found to have shorter operational lifetimes and larger degradation rates than first-generation cells in accelerated life testing, which has contributed to their somewhat limited deployment. Globally, the PV market share of thin-film technologies remains around 5% as of 2023. However, thin-film technology has become considerably more popular in the United States, where CdTe cells alone accounted for 29% of new utility-scale deployment in 2021.

History

    Early research into thin-film solar cells began in the 1970s. In 1970, Zhores Alferov's team at Ioffe Institute created the first gallium arsenide (GaAs) solar cells, later winning the 2000 Nobel prize in Physics for this and other work. Two years later in 1972, Prof. Karl Böer founded the Institute of Energy Conversion (IEC) at the University of Delaware to further thin-film solar research. The institute first focused on copper sulfide/cadmium sulfide (Cu₂S/CdS) cells and later expanded to zinc phosphide (Zn₃P₂) and amorphous silicon (a-Si) thin-films as well in 1975. In 1973, the IEC debuted a solar-powered house, Solar One, in the first example of residential building-integrated photovoltaics.In the next decade, interest in thin-film technology for commercial use and aerospaceapplications increased significantly, with several companies beginning development of amorphous silicon thin-film solar devices.Thin-film solar efficiencies rose to 10% for Cu₂S/CdS in 1980, and in 1986 ARCO Solar launched the first commercially available thin-film solar cell, the G-4000, made from amorphous silicon.

    In the 1990s and 2000s, thin-film solar cells saw significant increases in maximum efficiencies and expansion of existing thin-film technologies into new sectors. In 1992, a thin-film solar cell with greater than 15% efficiency was developed at University of South Florida. Only seven years later in 1999, the U.S. National Renewable Energy Laboratory and Spectrolab collaborated on a three-junction gallium arsenide solar cell that reached 32% efficiency.That same year, Kiss + Cathcart designed transparent thin-film solar cells for some of the windows in 4 Times Square, generating enough electricity to power 5-7 houses. In 2000, BP Solar introduced two new commercial solar cells based on thin-film technology.In 2001, the first organic thin-film solar cells were developed at the Johannes Kepler University of Linz. In 2005, GaAs solar cells got even thinner with the first free-standing (no substrate) cells introduced by researchers at Radboud University.

    This was also a time of significant advances in the exploration of new third-generation solar materials–materials with the potential to overcome theoretical efficiency limits for traditional solid-state materials. In 1991, the first high-efficiency dye-sensitized solar cell was developed, replacing the ordinary solid semiconducting (active) layer of the cell with a liquid electrolyte mixture containing light-absorbing dye. In the early 2000s, development of quantum dot solar cells began, technology later certified by the National Renewable Energy Laboratory in 2011. In 2009, researchers at the University of Tokyo reported a new type solar cell using perovskites as the active layer and achieving over 3% efficiency, building on Murase Chikao's 1999 work which created a perovskite layer capable of absorbing light.

    In the 2010s and early 2020s, innovation in thin-film solar technology has included efforts to expand third-generation solar technology to new applications and to decrease production costs, as well as significant efficiency improvements for both second and third generation materials. In 2015, Kyung-In Synthetic released the first inkjet solar cells, flexible solar cells made with industrial printers. In 2016, Vladimir Bulović's Organic and Nanostructured Electronics (ONE) Lab at the Massachusetts Institute of Technology (MIT) created thin-film cells light enough to sit on top of soap bubbles. In 2022, the same group introduced flexible organic thin-film solar cells integrated into fabric.

    Thin-film solar technology captured a peak global market share of 32% of the new photovoltaic deployment in 1988 before declining for several decades and reaching another, smaller peak of 17% again in 2009. Market share then steadily declined to 5% in 2021 globally, however thin-film technology captured approximately 19% of the total U.S. market share in the same year, including 30% of utility-scale production.