Solar cell and module manufacturers focus on improving the efficiency of PV devices to continue driving the already low costs further down. The share of PERC in commercial PV production has been increasing consistently on this account. In fact, PERC has become the new solar cell standard in the industry. On the other hand, many industry experts see PERC reaching its practical limit of 23% soon, maybe even as early as in a year's time.
Thus, the industry has started to look beyond PERC. There seem to be two main paths – passivated contacts and heterojunction. Both the technologies have entered mass production with a reasonable number of adopters. In our publication on High Efficiency Cell Technologies 2019 we provide an overview on the well-known advanced cell technologies with an emphasis on passivated contacts, HJT and the new incumbent PERC.
This first edition on high efficiency cell technologies builds on three annual reports that focused mostly on PERC. Now, that PERC is fully established, we are looking at the technologies that are likely to come next.
Since passivated contacts is the latest cell technology on the block, it is the first to be dealt with (Chapter 3). When it comes to manufacturing of passivated contacts, the core of the process lies in a three-step application of interfacial oxide, deposition of intrinsic polycrystalline silicon layers and doping of polysilicon. Like in the inception days of PERC, nearly every known deposition technology used in PV is promoted for this application though with different degrees of availability. LPCVD, PECVD, APCVD, PE ALD and PVD tools from various vendors are promoted for the core job of producing passivated contacts cells. However, LPCVD is the most widely used technology today; among others, because it was the first to be ready. Annealing and boron diffusion are the additional two production steps required to create passivated contacts when compared to PERC. Metallization is also a very important aspect for mass production of passivated contacts, especially requiring pastes compatible to be fired at relatively low temperature compared PERC.
Chapter 4 explains other advanced cell technologies based on n-type wafers but with much lesser interest from cell manufacturers, at least from today's perspective. These technologies include MoSon, which is essentially a metallization upgrade for n-PERT and 'low-cost' IBC.
The annual update on PERC technology is presented in Chapter 5. PERC is all about applying active passivation to the rear side of the standard cell. ALD and PECVD continue to be the main technologies used for this purpose. Interestingly, the dominance of these two technologies has been changing in the last few years – first it was inline PECVD tools, then batch type ALD, and as of recently batch PECVD tools are getting high traction. PERC as a technology is making tremendous progress and is the core of most major expansion plans. The installation base for PERC is expected to reach the 100 GW benchmark this year.
After providing in-depth information about HJT in the beginning of this year, the current publication highlights the most recent developments in the HJT segment in Chapter 6. The most crucial step in producing HJT cells is deposition. The first part of the deposition is applying doped and intrinsic amorphous silicon layers, while applying transparent conductive oxide (TCO) layers completes the deposition step. We provide an overview on different methods used for these two deposition steps along with the insight of the production equipment suppliers. When it comes to metallization of HJT, it closely follows the technology choice at the interconnection step of module making. The number of companies active in the field of HJT has been increasing – from both PV manufactures and equipment makers. Larger solar cell makers have started evaluating the technology, while a few have made the first steps towards commercial production of HJT.
The TaiyangNews Report on High Efficiency Solar Cell Technologies 2019 is for download free of charge here.