5 Changes in ZnO-based DSCs after storage in the dark
5.3 Changes in recombination during storage in the dark
5. Changes in ZnO-based DSCs after storage in the dark
-0.2 -0.3 -0.4 -0.5 -0.6 -0.7
100 101 102 103
D149 + CA (1 min) [45]
D149 + CA (1 min) [45] V_oc D149 + CA (15 min) [61]
D149 + CA (15 min) [61] V_oc D149 + CA (15 min) [61] dark D149 + LCA (15 min) [p22]
D149 + LCA (15 min) [p23]
D149 + LCA (15 min) [p25]
D14915minLCA [p25]
D149 + LCA (15 min) [p25] 4 weeks D149 + LCA (15 min) [p25] 4 weeks D149 + CA (1 h) [65]
D149 + CA (1 h) [65] V_oc D149 + CA (1 h) [65] dark D149 + CA (1 h) [TiO2-04]
D149 + CA (1 h) [TiO2-04] V_oc D149 + CA (1 h) [TiO2-04] dark DN91 (15 min) [48]
DN91 (15 min) [48]
DN91 (15 min) [48] V_oc DN91 (15 min) [66]
DN91 (15 min) [66] V_oc DN91 (15 min) [66] dark DN91 + LCA (1 min) [46]
DN91 + LCA (1 min) [46]
DN91 + LCA (1 min) [46] V_oc DN91 + LCA (15 min) [35]
DN91 + LCA (15 min) [35]
DN91 + LCA (15 min) [35] 4 weeks DN91 + LCA (15 min) [35] 4 weeks DN91 + LCA (15 min) [38]
DN91 + LCA (15 min) [40]
DN91 + LCA (15 min) [43]
DN91 + LCA (15 min) [43]
DN91 + LCA (15 min) [43] V_oc DN91 + LCA (15 min) [43] 4 weeks DN91 + LCA (15 min) [43] 4 weeks DN91 + LCA (15 min) [43] 4 weeks V_oc DN91 + LCA (15 min) [60]
DN91 + LCA (15 min) [60] V_oc DN91 + LCA (15 min) [60] dark DN91 + LCA (1 h) [TiO2-02]
DN91 + LCA (1 h) [TiO2-02] V_oc DN91 + LCA (1 h) [TiO2-02] dark DN91 + LCA (1 h) iodolyte [TiO2-06]
DN91 + LCA (1 h) iodolyte [TiO2-06] V_oc DN91 + LCA (1 h) iodolyte [TiO2-06] dark DN216 (15 min) [49]
DN216 (15 min) [49]
DN216 (15 min) [49] V_oc DN216 (1 h) [67]
DN216 (1 h) [67] V_oc DN216 (1 h) [67] dark DN216 + LCA (1 min) [55]
DN216 + LCA (1 min) [55] V_oc DN216 + LCA (1 min) [59]
DN216 + LCA (1 min) [59] V_oc DN216 + LCA (1 min) [59] dark DN216 + LCA (15 min) [52]
DN216 + LCA (15 min) [52] V_oc DN216 + LCA (15 min) [p29]
DN216
15min LCA [p29]
DN216 + LCA (15 min) [p29] 4 weeks DN216 + LCA (15 min) [p29] 4 weeks DN216 + LCA (15 min) [p30]
DN216
15min LCA [p30]
DN216 + LCA (15 min) [p30] 4 weeks DN216 + LCA (15 min) [p30] 4 weeks DN216 + LCA (15 min) [p31]
DN21615minLCA [p31]
DN216 + LCA (15 min) [p31] 4 weeks DN216 + LCA (15 min) [p31] 4 weeks DN216 + CA (1 h) [68]
DN216 + CA (1 h) [68] V_oc DN216 + CA (1 h) [68] dark DN216 + LCA (1 h) [70]
DN216 + LCA (1 h) [70] V_oc DN216 + LCA (1 h) [70] dark DN216 + LCA (1 h) [TiO2-01]
DN216 + LCA (1 h) [TiO2-01] V_oc DN216 + LCA (1 h) [TiO2-01] dark DN216 + LCA (1 h) [TiO2-05]
DN216 + LCA (1 h) [TiO2-05] V_oc DN216 + LCA (1 h) [TiO2-05] dark DN285 (15 min) [51]
DN285 (15 min) [51]
DN285 (15 min) [51] V_oc DN285 + LCA (1 min) [56]
DN285 + LCA (1 min) [56] V_oc DN285 + LCA (1 min) [57]
DN285 + LCA (1 min) [57] V_oc DN285 + LCA (1 min) [57] V_oc CYR DN285 + LCA (1 min) [57] dark DN285 + LCA (15 min) [34]
DN285 + LCA (15 min) [34]
DN285 + LCA (15 min) [34] 4 weeks DN285 + LCA (15 min) [34] 4 weeks DN285 + LCA (15 min) [63]
DN285 + LCA (15 min) [63] V_oc DN285 + LCA (15 min) [63] dark DN285 + LCA (15 min) [p24]
DN285 + LCA (15 min) [p26]
DN285 + LCA (15 min) [p26] 4 weeks DN285 + LCA (15 min) [p28]
DN285 + LCA (15 min) [p28]
DN285 + LCA (15 min) [p28] 4 weeks DN285 + LCA (15 min) [p28] 4 weeks DN285 + LCA (1 h) [71]
DN285 + LCA (1 h) [71] V_oc DN285 + LCA (1 h) [71] dark DN285 + LCA (1 h) [TiO2-03]
DN285 + LCA (1 h) [TiO2-03] V_oc DN285 + LCA (1 h) [TiO2-03] dark J102 (24 h) [54]
J102 (24 h) [54] V_oc Phosphon (overn.) [72]
Phosphon (overn.) [72] V_oc Phosphon (overn.) [72] dark Vinylcarbon (overn.) [73] V_oc Vinylcarbon (overn.) [73] dark D149
15min LCA [p25]
DN21615minLCA [p29]
DN216
15min LCA [p30]
DN21615minLCA [p31]
Rrec / cm2
V f or Vf - Ec/q / V
direkt 4 weeks
-0.2 -0.3 -0.4 -0.5 -0.6 -0.7
100 101 102 103
DN91
15min LCA [35]
DN9115minLCA [43]
DN91
15min
LCA [43] red LED DN285
15min LCA [34]
DN28515minLCA [p28]
Rrec / cm2
V f or Vf - Ec/q / V
direct 4 weeks
1018 1019
100 101 102 103
Rrec / cm2
DOS / eV-1 cm-3
1018 1019
100 101 102 103
R rec / cm2
DOS / eV-1 cm-3
Figure 52 – Recombination resistance of dye-sensitized cells sensitized with different indoline dyes plotted (a,b) against the Fermi level voltage (for measurements directly after preparation) or the voltage corrected by the conduction band edge shift (for measurements after 4 weeks storage in the dark), and (c,d) against the DOS. Filled symbols indicate measurements performed after the preparation of the cells, open symbols of the same color indicate a measurement of the same cell after storage in the dark for 4 weeks. Grey symbols half-filled or filled with red indicate measurements of cell [43] at red LED illumination directly after preparation or after 4 weeks storage in the dark, respectively. Adapted from 259.
Only for cell [43] directly after preparation, τn determined from OCVD measurements is considerably decreased compared to an ideally linear slope, indicating that recombination via the substrate occurs for this cell. However the OCVD measurement of the same cell after 4 weeks results in τn similar to other cells (the increase is indicated by a green arrow in Figure 53(b)), which indicates that recombination via the substrate is again efficiently blocked. Probably the defect leading to a decrease of the OCVD lifetime was small, and could be “healed” even by comparatively small changes which might occur in the cell during storage in the dark, for example by a rearrangement of surface adsorbates. This instance shows the high sensitivity of OCVD lifetime at lower absolute voltages for the indication of defects in the blocking layer, superior to VOC vs. illumination intensity (Figure 104, p.
210), where cell [43] measured after preparation showed no difference compared to all other cells.
(a) (b)
(c) (d)
-0.3 -0.4 -0.5 -0.6 10-3
10-2 10-1
DN216
15min LCA [p30]
DN21615minLCA [p31]
D149
15min LCA [p25]
DN216
15min LCA [p29]
Electron lifetime / s
Vf or V
f-E
c/q / V
EIS IMVS OCVD
-0.3 -0.4 -0.5 -0.6
10-3 10-2 10-1
DN285
15min LCA [34]
DN285
15min LCA [p28]
DN91
15min LCA [35]
DN91
15min LCA [43]
(red LED) DN91
15min LCA [43]
Electron lifetime / s
Vf or V
f-E
c/q / V
EIS IMVS OCVD
1018 1019
10-3 10-2
D14915minLCA [p25]
DN216
15min LCA [p29]
DN21615minLCA [p30]
DN216
15min LCA [p31]
Electron lifetime / s
DOS / eV-1 cm-3
direct 4 weeks
1018 1019
10-3 10-2
DN285
15min LCA [34]
DN285
15min LCA [p28]
DN9115minLCA [35]
DN91
15min LCA [43]
DN91
15min
LCA [43] red LED
Electron lifetime / s
DOS / eV-1 cm-3
direct 4 weeks
Figure 53 – Effective electron lifetimes of dye-sensitized solar cells, determined from EIS at AM1.5 illumination (symbols in (a,c,d)) and from IMVS (lines) and OCVD (symbols in (b)) measurements at red LED illumination. Filled symbols and solid lines indicate a measurement of a cell directly after preparation, while open symbols and dashed lines indicate cells measured after 4 weeks storage in the dark. (a) τn from EIS and IMPS vs. Vf ; (b) τn from OCVD vs. Vf; (c) τn from EIS and IMPS vs. Vf (measurements directly after preparation) or vs. Vf corrected by the conduction band edge shift (measurements after 4 weeks); (d) τn from EIS vs. the DOS. Grey symbols half-filled or filled with red indicate EIS measurements of cell [43] at red LED illumination measured before and after the storage in the dark, respectively. Adapted from 259.
A comparison of recombination currents in the dark and under illumination in Figure 54 gives information about regeneration, and also about the observed changes in VOC after ageing of the cells.
A direct comparison of the recombination current in the dark and under AM1.5 illumination for each cell shows that the recombination current at AM1.5 is always higher and has a different slope than the recombination in the dark. As also in the previous chapters, the difference in recombination for the different illumination conditions was ascribed mainly to enhanced recombination via oxidized dye molecules, and thus regeneration efficiency as one of the limiting factors of ISC. This effect is larger at lower absolute voltages (as the ISC is higher), which leads to the observation that for some cells the recombination current in the dark and under illumination intersect at more negative voltages.
(a) (b)
(c) (d)
5. Changes in ZnO-based DSCs after storage in the dark
-0.3 -0.4 -0.5 -0.6 -0.7
0.01 0.1 1 10 100
D14915minLCA [p25]
DN21615minLCA [p29]
DN21615minLCA [p30]
DN21615minLCA [p31]
Current density / mA cm-2
Vf or Vf - Ec/q / V
direct 4 weeks AM1.5 dark AM1.5 dark
-0.3 -0.4 -0.5 -0.6 -0.7
0.01 0.1 1 10 100
DN28515minLCA [34]
DN28515minLCA [p28]
DN9115minLCA [35]
DN9115minLCA [43]
DN91 + LCA (15 min) [35]
DN9115minLCA [35]
DN91 + LCA (15 min) [35] 4 weeks DN91 + LCA (15 min) [35] 4 weeks DN91 + LCA (15 min) [43]
DN9115minLCA [43]
DN91 + LCA (15 min) [43] 4 weeks DN91 + LCA (15 min) [43] 4 weeks DN216 + LCA (15 min) [p29]
DN216 + LCA (15 min) [p29]
DN216 + LCA (15 min) [p29] 4 weeks DN216 + LCA (15 min) [p29] 4 weeks DN216 + LCA (15 min) [p30]
DN216 + LCA (15 min) [p30]
DN216 + LCA (15 min) [p30] 4 weeks DN216 + LCA (15 min) [p30] 4 weeks DN216 + LCA (15 min) [p31]
DN216 + LCA (15 min) [p31]
DN216 + LCA (15 min) [p31] 4 weeks DN216 + LCA (15 min) [p31] 4 weeks DN285 + LCA (15 min) [34]
DN28515minLCA [34]
DN285 + LCA (15 min) [34] 4 weeks DN285 + LCA (15 min) [34] 4 weeks DN285 + LCA (15 min) [p28]
DN28515minLCA [p28]
DN285 + LCA (15 min) [p28] 4 weeks DN285 + LCA (15 min) [p28] 4 weeks
Current density / mA cm-2
Vf or Vf - Ec/q / V
direct 4 weeks AM1.5 dark AM1.5 dark
Figure 54 – Recombination currents for dye-sensitized solar cells sensitized with different dyes. The fermi-level voltage of each cell was corrected by the shift of the conduction band edge (shift after 4 weeks of storage time) to give Vc*, for cells sensitized with (a) D149, DN216, (b) DN91 or DN285. Absolute values of the dark current density vs. VC*. Currents measured at AM1.5 illumination are indicated by thick lines, measurements in the dark are indicated by thin lines.
Measurements directly after cell preparation are indicated by full lines, and measurements after storage in the dark for 4 weeks are indicated by dashed lines. Adapted from 259.
From the difference of Ireclight at the same relative position of Ec, the change in VOC by a change of the recombination current were determined after equation (33), see the values ΔVOC(Ireclight) in Table 12.
For most of the cells the change of VOC from the recombination current under illumination is positive, indicating that a higher value of VOC can be reached for aged cells due to a decrease of recombination.
With the values of ΔVOC from the increase in ISC and the change in Ec, the theoretical change in VOC
due to these three influences was calculated 17 and compared to the observed change in VOC after 4 weeks, see Table 12.
Table 12 – Voltage differences determined from Cµ, from the recombination current under illumination, from ISC, and from IV-curves; also the calculated voltage difference is listed. The differences are determined for each measurement after 4 weeks relative to the same cell measured directly after cell preparation. Negative values indicate a shift to less negative voltages (downward in energy), and positive values indicate shifts to more negative voltages. A mean value of β = 0.55 was used for the calculations. Table adapted from 259.
Cell 𝚫𝐄𝐜/𝐪 𝚫𝐕𝐎𝐂(𝐈𝐫𝐞𝐜𝐥𝐢𝐠𝐡𝐭) 𝚫𝐕𝐎𝐂(𝚫𝐈𝐒𝐂) 𝚫𝐕𝐎𝐂,𝐜𝐚𝐥𝐜 𝚫𝐕𝐎𝐂(𝐈𝐕) determined at Cµ
= 3 · 10-4 F cm-2
determined near VOC after equation (33)
after equation (32)
after equation (34)
Shift from IV-curve
Unit mV mV mV mV mV
D14915min
LCA [p25] -43 17 5 -21 -13
DN9115minLCA [35] -15 -5 4 -16 -13
DN9115min
LCA [43] -18 20 0 +2 +1
DN21615minLCA [p29] -27 25 5 +3 +6
DN21615minLCA [p30] -36 11 4 -21 -16
DN21615minLCA [p31] -11 1 4 -6 -5
DN28515min
LCA [34] -10 0 6 -4 -2
DN91 LCA [p28] -36 17 4 -15 -9
(a) (b)
The different influences contribute to the overall change in VOC by different amounts, for most cells the increase in ISC leads to a relatively small change in VOC by about 5 mV, while larger ΔVOC is found for the influence of recombination and Ec. A good consistency is found for the measured and calculated values of ΔVOC for the majority of the cells, with a deviation of not more than ±3 mV. For cells [p25], [p30] and [p28] the deviation of the calculated and measured ΔVOC is larger, which is mainly attributed to a different slope of the recombination currents under illumination (before and after storage in the dark) for these cells, which complicates the exact determination of ΔVOC. For cell [p25] also deep monoenergetic trap states were observed in Cµ, which in literature was mentioned as a possible reason for a deviation of ΔVOC,calc from ΔVOC(IV) 17. The maximum deviation of ΔVOC,calc
from ΔVOC determined from the IV-curves was about -7 mV, which renders this method of the determination of different influences on VOC very useful.