Efficient Dye-Sensitized Solar Cell Based on oxo-Bacteriochlorin Sensitizers with Broadband Absorption Capability
Efficient Dye-Sensitized Solar Cell Based on oxo-Bacteriochlorin Sensitizers with Broadband Absorption Capability
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DOI：
10.1021/jp900328u
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发表时间：
2009-05-07
影响因子：
3.7
通讯作者：
Sasaki, Shin-ichi
中科院分区：
文献类型：
--
作者：
Wang, Xiao-Feng;Kitao, Osamu;Sasaki, Shin-ichi
合成了两种具有稳定细菌卟吩骨架的染料敏化剂，即甲基反式 - 3(2)-羧基 - 8 - 去乙基 - 7 - 乙基 - 8 - 氧代 - 焦脱镁叶绿酸 - a（BChlorin - 1）和甲基反式 - 3(2)-羧基 - 7 - 去甲基 - 8 - 甲基 - 7 - 氧代 - 焦脱镁叶绿酸 - a（BChlorin - 2），并将它们应用于染料敏化太阳能电池。由于Q(x)跃迁偶极上两个吡咯环的部分饱和，这两种敏化剂在整个可见光区域都能吸收光。当它们沉积在TiO₂薄膜上时，敏化剂的J - 聚集体部分形成，产生宽且红移的Q(y)带。BChlorin - 2在TiO₂薄膜上的表面覆盖度比BChlorin - 1大得多，这表明前者敏化剂在TiO₂表面形成更严重的聚集，这可能导致更多的激子湮灭，从而降低太阳能电池的光电流。通过密度泛函理论（DFT）计算得到的两种敏化剂的前线分子轨道没有明显差异。对染料 - TiO₂ - Na模型体系的进一步计算表明，BChlorin - 1中额外的LUMO + 2轨道也可能导致光电流的差异。BChlorin敏化太阳能电池中较大的光电压归因于染料 - TiO₂界面中较低效的电荷复合，从而产生更长的电子寿命（τ）。电解液中额外的4 - 叔丁基吡啶显著降低了太阳能电池的光电流和太阳能 - 电能转换效率（η），尤其是当使用BChlorin - 2作为敏化剂时。这种显著的降低归因于TiO₂的导带边（CBE）向敏化剂的分子费米能级（MFL）上方的负电位移动，并抑制了从敏化剂的MFL到TiO₂的CBE的电子注入。BChlorin - 1与鹅去氧胆酸（CDCA）的共吸附可以打破染料聚集体，并提高吸收带最大值处的入射光子 - 电流转换效率。与CDCA共吸附的BChlorin - 1敏化太阳能电池比没有CDCA的电池具有更长的电子寿命和更大的扩散系数。通过在溶液中与5 mM CDCA共吸附，BChlorin - 1敏化太阳能电池在空气质量AM 1.5（100 mW cm⁻²）光照下表现出最高性能，短路光电流 = 18.4 mA cm⁻²，开路光电压 = 0.54 V，填充因子 = 0.66，η = 6.6%。
Two dye sensitizers, methyl trans-3(2)-carboxy-8-deethyl-7-ethyl-8-oxo-pyropheophorbide-a (BChlorin-1) and methyl trans-3(2)-carboxy-7-demethyl-8-methyl-7-oxo-pyropheophorbide-a (BChlorin-2), with stable bacteriochlorin skeletons were synthesized and applied to dye-sensitized solar cells. Both sensitizers absorb the light all over the visible region owing to partial saturation of the two pyrrole rings on the Q(x) transition dipole. When they were deposited on a TiO2 film, the J-aggregates of the sensitizers are partially formed to give broad and red-shifted Q(y) bands. The surface coverage of TiO2 film by BChlorin-2 is much larger than by BChlorin-1, suggesting the former sensitizer forms more serious aggregation on the surface of TiO2, and this could cause more exciton annihilation to reduce the photocurrent of solar cell. The frontier molecular orbitals of both sensitizers obtained from the DFT calculations show no distinguishable difference. Extended calculations on the dye-TiO2Na model system suggest that additional LUMO + 2 orbital in BChlorin-1 may also contribute to the difference in photocurrent. The larger photovoltage in BChlorin-sensitized solar cell was attributed to a less efficient charge recombination in the dye-TiO2 interface to give a longer electron lifetime (tau). Additional 4-tert-butylpyridine in the electrolyte significantly reduced the photocurrent and the solar energy-to-electricity conversion efficiency (eta) of the solar cells, especially when BChlorin-2 was employed as a sensitizer. This dramatic decrease was attributed to the shift of conduction band edge (CBE) of TiO2 to a negative potential above the molecular Fermi level (MFL) of the sensitizers and suppressed the electron injection from the MFL of sensitizer to CBE of TiO2. Coadsorption of BChlorin-1 with chenodeoxycholic acid (CDCA) could break the dye aggregate and improve the incident photon-to-current conversion efficiency at the absorption bands maxima. BChlorin-1 sensitized solar cells coadsorbed with CDCA gave a longer electron lifetime and a larger diffusion coefficient than the cell without CDCA. By coadsorbing with 5 mM CDCA in solution, the BChlorin-1 sensitized solar cell gave a highest performance with short-circuit photocurrent = 18.4 mA cm(-2), open-circuit photovoltage = 0.54 V, fill factor = 0.66, and eta = 6.6% under the air mass AM 1.5 (100 mW cm(-2)) illumination.