Common (PV) technologies are absorbing the visible solar spectrum as it includes the highest photon flux domain and it is where the theoretical Shockley-Queisser limit is maximum. The general concept of PV technology relies on black absorbers.  As a corollary, PV devices are aesthetically not transparent, fulfilling plenty performance aspects. For higher-tech or architectural applications, see-through technologies are bringing important innovation paving the way to new integration opportunities. In this case, the level of average visible transparency (AVT) can be modulated either through partially segmented p-n junction or by decreasing non selective absorber thickness. Another approach is to develop selective absorbers. For this, the NIR part is a target since it composes ca. 51% of the total solar spectrum. Selective NIR absorption can only be achieved by molecular-based technologies. This is the case for luminescence solar concentrators, organicPV and dye-sensitized solar cells. The practical PCE limit of a single junction NIR-selective transparent PV (TPV) with an AVT of 100% is 10.8%.[1] LSC reaches the highest level of AVT, up to 88%, however with PCEs lying well-below 1%.[2] OPV reached a PCE of 4% with an AVT of 64% by adopting a bulk heterojunction. The American company Ubiquitous Energy achieved 5.1% PCE with an AVT of 51.5%.[3-4]

The optical rendering of DSSC is particularly advantageous since both coloration and transparency can be adjusted. Only semi-transparent DSSC has been proposed so far. Han et al. reported a green see-through DSSC with a PCE of 3.7% and a transmittance maximum of 60% at 560nm[5], Mallick et al. reported a semi-transparent DSSC based on N719 achieving a PCE of 2.4% and an AVT of 44%[6]. Demadrille et al. also reported a photochromic semi-transparent DSSC achieving AVT of 59% in dark and 27% under illumination affording in the latter case a PCE of 3.7%.[7] 

In this communication, we will describe our recent achievements in the development of NIR-selective dyes which design principle relies in reaching intense S0-S1 transition beyond 800nm while rejecting the upper S0-Sn transitions far in the blue where the human retina is poorly sensitive.[8]  Thanks to a holistic reduction of all internal optical losses and coloration tracking, we demonstrate the relevance of NIR-DSSC for TPV applications, achieving PCEs over 4%, AVT above 80% and color rendering index above 96%. Such characteristics confer to the selective NIR-DSSC never reached aesthetic features in terms of transparency and coloration.