Chlorophyll‐Based Organic–Inorganic Heterojunction Solar Cells

Abstract

Solid-state chlorophyll solar cells (CSCs) employing a carboxylated chlorophyll derivative, methyl trans-3 -carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO , on which four zinc hydroxylated chlorophyll derivatives were spin-coated for hole transporter chlorophylls (HTCs), are described. Key parameters, including the effective carrier mobility of the HTC films, as determined by the space charge-limited current method, and the frontier molecular orbitals of these DSCs and HTCs, as estimated from cyclic voltammetry and electronic absorption spectra, suggest that both charge separation and carrier transport are favorable. The power conversion efficiencies (PCEs) of the present CSCs with fluorine-doped tin oxide (FTO)/TiO /DSC/HTCs/Ag were determined to follow the order of HTC-1>HTC-2>HTC-3>HTC-4, which coincided perfectly with the order of their hole mobilities. The maximum PCE achieved was 0.86 % with HTC-1. The photovoltaic devices studied herein with two types of chlorophyll derivatives as dye sensitizers and hole transporters provide a unique solution for the utilization of solar energy with a view to truly realizing "green energy".

In Depth Analysis of Photovoltaic Performance of Chlorophyll Derivative-Based “All Solid-State” Dye-Sensitized Solar Cells

“…The introduction of cyano electron-withdrawing groups in chlorins M5-M6 indeed Compared to the D102 performances, those obtained with chlorin dyes were low (Table 3). Nevertheless, only a few publications have described the fabrication of ssDSSCs with chlorophyll derivatives and the values obtained here are in line with those reported [31]. They were even better than the performances obtained in some liquid-DSSCs with other chlorophyll derivatives [47][48][49][50].…”

“…Indeed, the M6 LUMO moved down below the TiO 2 conduction band edge energy level, no longer allowing exergonic electron injection to TiO 2 upon (HOMO → LUMO) optical transition, thus, explaining the decrease in PCE of M6 compared to M4. The energy levels of HOMO and LUMO of M2, M4, and M6 dyes are in the same range as those previously reported in the literature [31,33,52].…”

“…The binding of the chlorin dyes onto the TiO 2 surface leads to a broadening of the absorption bands, probably due to π stacking interactions between chlorin dye molecules, as extensively studied in previous investigations [37]. The comparison of the chlorin absorption spectra in THF solutions as the monomeric species ( Figure 1a) and on TiO 2 as aggregates also reveal that the Q Y bands shift to longer wavelengths suggesting the formation of J aggregates [31]. The π stacking of dyes when grafted onto the TiO 2 surface was evidenced from the UV-Visible absorption spectra, as discussed above.…”

“…The use of chlorophyll derivatives as sensitizers has been investigated in liquid electrolyte-based DSSCs leading to energy-to-electricity conversion efficiency (η) up to around 8% [28][29][30]. Concerning solid-state DSSC, there are only a few reports in the literature describing the use of chlorophyll a derivatives as dye [31][32][33].…”

Semisynthetic Chlorophyll Derivatives Toward Solar Energy Applications

“…To further improve the efficiency of the aforementioned device by modifying the HTM, two zinc Chls ZnChl‐48 and 50 (C3 1 ‐OMe analog of ZnChl‐48) and Pors ZnPor‐4 and 5 (Zn Pors with the same substitutents as ZnChl‐48 and 50) were investigated in the same device structure . The carrier mobility of ZnChl‐48 was as high as 4.11 × 10 −3 cm −2 V −1 S −1 due to the well‐ordered structure of J ‐type aggregates.…”