## 6 Discussion
### N-Type Crystalline Silicon Modules and Thin-Film Modules  
2018 was the first year when the annual new PV build exceeded 100 GW. Among all modules installed in 2018, 97% were of crystalline silicon types and only 3% were categorized as thin film modules, mainly supplied by First Solar (Tempe, AZ, USA) adopting cadmium telluride (CdTe) technologies and Solar Frontier (Tokyo, Japan) making copper indium selenium (CIS) products. While these thin-film modules have achieved efficiencies comparable to multicrystalline silicon products, their costs did not drop as rapidly as the c-Si peers. Considering the established advantages and  
Figure 12: Two installation profiles of modules with mini frames. Figure 13: One-axis trackers designed for bifacial modules. sustainable approaches to even lower cost and higher efficiency for c-Si PV modules, it is unlikely for thin film to grow to a dominant share in the next 10 years. Looking into the general category of crystalline silicon PV modules, it can be further separated into more sub-groups depending on the definition. The most popular sub-grouping is multi- vs. monocrystalline silicon PV, based on the crystalline structure quality of wafers. Alternatively, based on the doping materials in wafers, c-Si can be divided into negatively doped (with boron) and positively doped (with phosphorous), or simplified referred in industry as \(n\)-type and \(p\)-type c-Si PV. \(N\)-type cells allow higher efficiencies, as the excited electrons in \(n\)-type wafers can travel a longer distance before they return to the useless bonded status. However, they are more expensive to make. From the perspective of optimal economics at the system level, the industry showed more preference towards \(p\)-type c-Si PV (Figure 14). When cell structure is involved in categorizing PV modules, there are more options (Figure 15). Note that not every combination of different metrics has commercial applications because some combinations have poor economic value. For instance, there are no \(p\)-type IBC or HIT in the market, although theoretically such products can be made. Their absence from the market is because realizing these special cell structures necessitates higher production costs, but the \(p\)-type wafers cannot allow the advanced cell structures to fully display their capabilities of boosting efficiency and therefore do not justify the commercial production of such cells or modules. BloombergNEF observed a rising market share of PV modules with higher efficiencies, and expects the same trend to continue. However, \(p\)-type crystalline silicon PV modules are still likely to dominate in the near future, although monocrystalline silicon will win over its multi-peers soon. Figure 14: 2018 global PV module shipment by product type. Figure 15: Market share of different c-Si PV modules. Note: IBC is short for interdigitated back contact. HIT: heterojunction with intrinsic thin layer. PERC: passivated emitter and rear cell. PERL: passivated emitter, rear locally-diffused. PERT: passivated emitter, rear totally-diffused. Al-BSF: aluminum back surface field. Source: BloombergNEF. When comparing the economics of different types of modules, more metrics should be brought into consideration besides module efficiency. Two important ones are temperature coefficient and degradation rate. While the module efficiency is measured under standard testing conditions, the actual operation environment varies constantly, and modules with the same area and efficiency (and thus the same nameplate capacity) but different materials or cell structures could generate different yields.