IPVF's PV technology vision for 2030

Current single‐junction crystalline silicon (c‐Si) solar cells are approaching their power conversion efficiency (PCE) limit. Tandem solar cells are expected to overcome such efficiency limit, with perovskite on c‐Si tandems being a promising candidate for commercialization over the next years. This work aims atdescribing the conditions that tandem cells and modules need to fulfill to successfully enter the market in 2030.We first estimate that industrial c‐Si photovoltaic modules may reach a price level of about 15 c$/W in 2030 at a PCE of 22–24%, with an expected lifetime of 30 years and an annual degradation of 0.5%. For commercial relevance, we anticipate that tandem module efficiencies need to be increased to reach around 30%, while matching lifetime and degradation rate of c‐Si modules. Provided these conditions, we find that these tandem modules could then have a cost bonus of around 5–10 c$/W compared to c‐Si modules for reaching equal levelized cost of energyvalues.

To assess the competitiveness of tandem PV modules vs. c-Si modules in 2030, we use an iso-LCOE approach, i.e. we determine the price difference between tandem and c-Si modules that results in the same LCOE value, dependent on the lifetime, degradation, financing conditions etc. of tandem modules. Figure 1 outlines the approach: from the expected cumulative PV installation in 2030, we determine a possible c-Si module price range from the learning curve. As this range will be rather broad, also depending on the learning rate used for the extrapolation, we use a comparison with module materials cost data for 2030 and current module market prices to eliminate the very low and high price ranges (i.e. below materials cost or above current market price). This c-Si module price value is then used together with the extrapolated module efficiency to 2030 in an LCOE calculation for two different PV system sizes and locations to determine the costbonus/malus of tandem vs. c-Si modules, as an indicator of the competitiveness of tandem modules in the PV market in 2030.

| CURRENT PV TECHNOLOGIES
The PV module market is dominated by c-Si technology with a market share of about 95%, whereas thin-film technology, mainly cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), has a F I G U R E 1 Approach used to determine the costbonus or malus (i.e. competitiveness) of tandem vs. c-Si PV modules at iso-LCOE for 2030 F I G U R E 2 Historical evolution of mainstream (Al-BSF/PERC) industrial crystalline silicon solar cell and module power conversion efficiencies (from refs. [6,8,10] As well as internal data) and extrapolation towards 2030, using the Pearl-Reed function 9 to take the practical efficiency limit of c-Si solar cells of 27% (low scenario) and the theoretical limit of 29.4% (high scenario), respectively, into account. ITRPV expectations for IBC cells are shown for comparison 11 market share of about 5%. 2  However, c-Si solar cells are approaching the practical PCE limit which is thought to be in the 27% efficiency range (see e.g. 4,7 ). Average industrial solar cell and module efficiencies have increased over the last years by 0.4-0.6% abs. per year. 6 presents an s-shaped form that describes an accelerated growth at the beginning, followed by a slowing down after reaching half of the possible improvement: with n(t) = time-dependent efficiency, L = upper limit of n(t), a = location coefficient and b = shape coefficient.

| MULTIJUNCTION PV CELLS AND MODULES
In order to further increase cell and module efficiencies and thereby leveraging balance of system (BOS) costs, tandem solar cells and modulesare expected to be introduced in the market from around 2023 onwards. 11 Such tandem solar cellshave a theoretical efficiency limit of >40%. 15 Various materials combinations for tandem cells are currently under investigation, the most prominent being perovskites on c-Si, 16 III-V on c-Si, 17 III-V on III-V, 18 28 Note however that this is the so-called "bifacial-equivalent efficiency" that assumes 20% of standard irradiance also impinging onto the rear side of the bifacial cell and that must not be confused with the power conversion efficiency PCE.  [30,31]. These studies seem to bode well for the future recycling of commercial perovskite on c-Si tandem modules.

| PV MARKET DEVELOPMENT AND PRICE EVOLUTION BASED ON THE PV MODULE LEARNING CURVE
Addressing the evolution of the PV market, it is obvious that historically the market growth has repeatedly been underestimated so far, see e.g. ref. [32]. Recent estimates predict a cumulative installed PV capacity in 2030 ranging from 1.29 TW 33 to 5.01 TW, 34 see Table 1.
Applying IEA current policies and the Shell sky scenario as the lower and upper estimates for cumulative shipments, we use the learning curve of PV modules to extract a target range of PV module prices that can be expected in 2030, see Figure 3. The learning curve can be expressed as with C (qt) = quantity-dependent module price, q0 = accumulated module shipments in year 0, t = time, qt = accumulated shipments in year t and b = constant. 37 The learning rate (LR)which describes the price change with a doubling of cumulative shipments is 37 The learning curve describes the price reduction per watt peak of PV modules with increasing cumulative shipments. This price reduction mainly results from economy of scale and only to a smaller extent from an increase in the PCE. 11    We anticipate that perovskite on c-Si tandem modules, which can build upon a > 100 GW c-Si module production base, might first be deployed in constrained area markets as a premium product, competing with SHJ and IBC premium c-Si modules. Such an introduction of the novel material perovskite in the PV market could then help in decreasing the hurdles for bankability associated with technology risks of novel materials. Note that there can also be specific incentives for the market introduction of a novel high-efficiency technology (such as China's Top Runner program currently 46 ) that can facilitate gaining extended field experience to demonstrate module performance, and in particular reliability, for subsequent large-scale deployment.
Current and future work at IPVF therefore focuses on the development of low-cost, high-efficiency tandem modules mainly using perovskite on c-Si, but also alternative technologies based on combinations with III-V materials. 47 While we have achieved first promising results for perovskite on c-Si tandem cells, 48 we are committed to demonstrate a tandem cell with a PCE of >30% that can be commercialized before 2030, with the help of national and international academic and industrial collaborations.