Abstract
CdTe is a very robust and chemically stable material and for this reason its related solar cell thin film photovoltaic technology is now the only thin film technology in the first 10 top producers in the world. CdTe has an optimum band gap for the Schockley-Queisser limit and could deliver very high efficiencies as single junction device of more than 32%, with an open circuit voltage of 1 V and a short circuit current density exceeding 30 mA/cm2. CdTe solar cells were introduced at the beginning of the 70s and they have been studied and implemented particularly in the last 30 years. The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell efficiency of 22.1% and a module efficiency of 19%. In this paper we describe the fabrication process following the history of the solar cell as it was developed in the early years up to the latest development and changes. Moreover the paper also presents future possible alternative absorbers and discusses the only apparently controversial environmental impacts of this fantastic technology.
Highlights
The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell efficiency of 22.1% and a module efficiency of 19%
In former times, very promising efficiencies around 11–12% were obtained by a Japanese group, the large thickness is a strongaround limitation for this technology very promising efficiencies were obtained by a Japanese group, the large thickness is a strong limitation for this technology [45]
CdTe solar cells have shown an extraordinary efficiency improvement in recent years. This was obtained by a complete redesign of the device with the (1) development of a stable and efficient back contact that works as well as back reflector, (2) band gap tuning by introduction of CdSex Te1−x in the CdTe absorber, (3) substitution of CdS with MZO
Summary
CdTe solar cell thin film photovoltaic technology was introduced in the early seventies of the last century [1] and it is the only thin film technology in the first 10 top producers in the world [2]. The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device, removing CdS and considering new features such as band gap grading, copper embedding, and more transparent n-layer. First Solar have delivered a 21.5% efficiency device [6] later improved to 22.1% [7], the stunning fact is that these results have been gained from materials obtained from the production line This demonstrates the high potential in terms of scalability of this technology, a large area module of 19% has been delivered [7].
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