From 2020 on, solar PV - with bifacial passivated emitter and rear cell (PERC) technology - had been crowned to the new king of energy markets [1], reaching extremely low offers in bids in the Middle East and North African (MENA) states such as Saudi Arabia, drawing prices as low as 0.01 US$/kWh [2] in 2021. The economy of the PV market completely changed since then, as it is not dominated by the demand, but by possible supply at the moment which is mostly limited by the supply of poly-Si to about 180 GWp in 2021 [3]. This was limiting the number of installations in 2021. However, the solar cell manufacturing capacity is around 300 GW (also including old Al-BSF lines), whereas the module capacity is at 250 GW [4]. The total installed PV capacity end 2021 was about 900 GWp and, in March 2022, 1 TWp was reached [5]. About 7 years later, we will enter a yearly 1 TWp market [6], where it is not wise and also not possible to produce all poly-Si, silicon (Si), wafers, cells, and modules in China. Local production will be needed everywhere to reach our ambitious goals of a fast and sustainable energy transition.

n-type silicon (Si) technologies played a major role in the early age of photovoltaics (PV). Indeed, the Bell Laboratories prepared the first practical solar cells from n-type crystalline Si (c-Si) wafers (Figure 3.1) [1-3]. Therefore, the domination of p-type technologies over the last decades for the production of commercial solar cells could appear as a paradox. This is essentially explained by historical reasons. Fifty years ago, the dominant market for c-Si solar cells was space power applications. In space, solar components are affected by radiation damages (electrons, protons). Interestingly, this degradation is significantly reduced by using p-type cells instead of n-type devices [4]. Thus, the solar cell developments for space applications focused on p-type wafers. When the first commercial productions for terrestrial applications were launched, they took benefit of these early developments for space missions and were therefore naturally based on p-type devices. Then, with the rapid growth of PV, p-type solar cells were the main recipients of the industrially oriented innovations and eventually maintained their domination over the PV market.

Even if usually n-type technologies are referred to cells & modules based on n-type silicon, the photovoltaic (PV) system adapted to n-type has evolved to be adapted to the new requirements. In this chapter, we will present an overview of PV systems considering all components to reach the connection and provide energy. We will also discuss about the efforts and innovation done to decrease levelized cost of energy (LCOE) considering that today, module and balance of system (BoS) are the main drivers of LCOE. Around 30% of the PV system cost is the module and over 60% concerns other components [1]. Thus, working in the BoS part and adapting components to the installation become more and more important for PV cost reduction and competitiveness. Finally, an improved design can also improve operation and maintenance (O&M) strategy and costs, making a double benefit in LCOE reduction.

In this chapter, we have reviewed candidates for further enhancement of cell efficiencies beyond those of today's mainstream PERC cells, with a focus on technological aspects rather than, e.g. cost. Regarding silicon single junctions, the prevalent theme is the use of carrier-selective passivating contacts, CSPCs. Of these, silicon heterojunction and polysilicon-on-silicon oxide (TOPCon/POLO) are most advanced and have enabled record high efficiencies above and close to 26%, respectively, on n-type silicon wafers. Further important topics are bifacial cell designs, which can be applied to different PV technologies. Single-side efficiencies above 25% have been achieved on bifacial TOPCon and bifacial SHJ solar cells. With proven bankability, bifacial PV products can be expected to gain more momentum in future development. In contrast, contacts based on metal compounds have yielded remarkable results in the last decade, yet failing to clearly evidence a significant advantage compared to the ones based on silicon. Further research is needed to unravel the material combination that would enable the long-awaited ultimate passivating contact for Si solar cells.

The second major topic are tandem and multijunction cells. This is the technology to move beyond the ultimate efficiency barrier of 29.4% for silicon PV and indeed, efficiencies well above 29% have been demonstrated in the lab for Si-based tandems. We have reviewed the current state of the art in lead halide perovskite-silicon tandems as well as III-V/silicon tandems. The former have reached a record PCE of 32.5% in monolithically integrated 2-terminal tandems, while III-V/Si 2T tandems currently stand at 23.4%. However, in III-V-Si devices, the number of absorbers has already been increased further, to three: in triple junction III-V/III-V/Si cells, PCEs of 35.9% have been realized with both 2T and 4T architectures. With a substantially higher cost for the III-V technology as compared to perovskites, but still inferior long-term stability in perovskites, as well as challenges in upscaling for both technologies, it remains to be seen which one of these technologies will gain an advantage. It should be mentioned that an important difference between reported silicon single junction and tandem/multijunction record devices is the cell area: while the single junction Si record devices have "industrial-size" active areas of several tens of cm² or even full wafers, record tandem cells are lab-scale 1-4 cm². Thus, up-scaling of tandem cells will remain an important topic in the near future.

At any rate, it can be expected that the exponential growth of PV as well as the diversity of applications (utility, rooftop and BIPV, agri-PV, etc.) will create ample opportunity for the market entry of quite a few of the mentioned technologies, and even for entirely new concepts such as three-terminal tandems or, at the module level, integrated PV and storage systems.