Efficiency Enhancement of Organic and Thin-Film Silicon Solar Cells with Photochemical Upconversion

Abstract

The efficiency of thin-film solar cells with large optical band gaps, such as organic bulk heterojunction or amorphous silicon solar cells, is limited by their inability to harvest the (infra)red part of the solar spectrum. Photochemical upconversion based on triplet–triplet annihilation (TTA-UC) can potentially boost those solar cells by absorbing sub-bandgap photons and coupling the upconverted light back into the solar cell in a spectral region that the cell can efficiently convert into electrical current. In the present study we augment two types of organic solar cells and one amorphous silicon (a-Si:H) solar cell with a TTA-upconverter, demonstrating a solar cell photocurrent increase of up to 0.2% under a moderate concentration (19 suns). The behavior of the organic solar cells, whose augmentation with an upconverting device is so-far unreported, is discussed in comparison to a-Si:H solar cells. Furthermore, on the basis of the TTA rate equations and optical simulations, we assess the potential of TTA-UC augmented solar cells and highlight a strategy for the realization of a device-relevant current increase by TTA-upconversion.

Photochemical upconversion: present status and prospects for its application to solar energy conversion

“…Indeed we have found that this model describes the measured QE data of TTA-UC-enhanced solar cells of various types very well, as can be seen for the example of a P3HT:ICBA organic bulk heterojunction solar cell 95 in Fig. 7.…”

“…91 For a useful review on upconversion nanophosphors for solar cell applications, see the recent review of Ramasamy et al 92 In 2012, our group demonstrated the first solar cell assisted by triplet-triplet annihilation upconversion, using the example of an amorphous silicon thin-film solar cell. 47,93,94 The approach was successively applied to organic solar cells 95 as well as dye-sensitized solar cells. 96 Details about these results and a comparison to the lanthanoid upconversion system are given below.…”

“…102,103 In order to minimize parasitic absorption, the overlap between the emission band of the TTA emitter and the absorption bands of both emitter and sensitizer must be minimized. Figure 5 shows the situation for two TTA solutions employed in our studies, 47,93,95 plotted for typical concentrations. It can be seen that there are slight overlaps between the rubrene emission and its own absorption band (self-absorption) as well as with the porphyrin sensitizer Q-and Soret bands.…”

“…In our recent publication we have combined two different organic bulk heterojunction cells with a semitransparent design with an external UC unit. 95 We further adapted a DSSC to host the upconvertor inside the device. 96 3.5.1 Organic solar cells.…”

Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

“…Consequently, tremendous advancements have been achieved in photochemical upconversion by using metal-containing triplet sensitizers with a variety of organic-based triplet acceptors/annihilators in both fluid solution [20,22,[29][30][31][32] and various host matrices [33][34][35][36][37][38][39][40][41][42][43]. The ultimate goal of this research is to maximize the efficiency of real-world solar powered devices by imparting sub-bandgap sensitization via integration of UC technology [8][9][10]44,45]. This change in cell design should reduce the drastic losses owing to spectral mismatch between various sensitizers and semiconductor bandgaps.…”