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Power generating reflective-type liquid crystal displays using a reflective polariser and a polymer solar cell.

Ho Huh Y, Park B - Sci Rep (2015)

Bottom Line: We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD.The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17-19.We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrophysics, Kwangwoon Univ., Wolgye-Dong, Nowon-gu, Seoul 139-701, Korea.

ABSTRACT
We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD. The PSC consisted of a polymer bulk-heterojunction photovoltaic (PV) layer of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] and [6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PCBM70), and showed a high power conversion efficiency of about 5%. In order to improve the visibility of the Solar-LCD, between the TN-LC and the PV cells we inserted a reflective polariser of a giant birefringent optical (GBO) film. The reflectivity from the Solar-LCD was observed to be considerably increased by more than 13-15% under illumination by visible light. The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17-19. We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices.

No MeSH data available.


Voltage-dependent reflectance (blue curves) and short-circuit photocurrent density (red curves) characteristics of the reflective-type Solar-LCD in the normal white (a) and black (b) modes under green (upper), blue (middle), and red (lower) illumination.The inset in (a) shows the temporal responses of reflectance from the Solar-LCD with a 2.0 V square-wave voltage applied.
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f4: Voltage-dependent reflectance (blue curves) and short-circuit photocurrent density (red curves) characteristics of the reflective-type Solar-LCD in the normal white (a) and black (b) modes under green (upper), blue (middle), and red (lower) illumination.The inset in (a) shows the temporal responses of reflectance from the Solar-LCD with a 2.0 V square-wave voltage applied.

Mentions: Next, in order to investigate the dual functionality of the reflective-type Solar-LCD, consisting of the GBO reflecting polariser between the TN-LC cell and the isotropic PCDTBT:PCBM70 PSC, we measured its electro-optical characteristics (Fig. 4). Figure 4(a) shows the reflectance characteristics of the reflected output from the device as a function of the voltage applied (Vapp) to the TN-LC cell in the NW mode under B(442 nm), G(532 nm), and R(633 nm) light. Here, the absolute reflectance is denoted by R0 for zero voltage and becomes saturated with increasing Vapp; the applied voltage that produces a relative brightness of 90% is termed the threshold voltage Vth, and the applied voltage that produces a relative brightness of 10% is termed the saturation voltage Vsa. The application of any voltage over Vth to the TN-LC cell causes the LC molecule to become vertically aligned. It can be seen (Fig. 4(a)) that in the voltage-off state (low voltage), the incident linearly polarised light passing through the front polariser changes its polarisation such that it is perpendicular to the front polariser following propagation through the TN-LC cell, and the light then reflects from the rear GBO polariser and passes again through the TN-LC cell and the front polariser. The reflectance is therefore high (R0 ~ 13–15%), representing the bright reflection state for Vapp < Vth (0.75 V). Moreover, when the voltage applied to the TN-LC cell Vapp > Vth, the effective birefringence and retardation value decrease to zero, and the amount of reflected light decreases, resulting in light absorption by the bottom PSC. The results of the measurements were: Vth = 0.70 V, Vsa = 1.10 V, R0 = 15.1% (for G), and the absolute reflectance at Vsa was 0.9%. Therefore, the contrast ratio of the intensity of bright to dark (IBRIGHT/IDARK) increases, reaching a maximum value of ca. 18.1, 18.1, and 17.5, for R, G, and B light, respectively, i.e., over a wide range of wavelengths of incident light. This contrast ratio clearly increases at high voltages, and the threshold voltage for the bright state is only about 0.75 V, which makes it suitable for a variety of applications, although the contrast ratio value at a given voltage differs slightly for each colour due to the variation in the phase retardation of the TN-LC cell. At the same time, we also assessed the power-generating abilities of the bottom PSC in terms of the short-circuit photocurrent from the Solar-LCD as a function of the voltage applied to the TN-LC cell in NW mode under B, G, and R light, as also shown in Fig. 4(a). Here it can clearly be seen that in the voltage-on state, the bottom PSC in the Solar-LCD generated an output photocurrent density Jsc of more than 0.40 mA/cm2 per unit of incident light power density (mW/cm2, green) for Vapp above Vsa (1.10 V), because incident light passed through the GBO reflecting polariser, whereas Jsc decreased markedly to 0.05 mA/cm2 when Vapp < 0.7 V. The measured response times are also shown in the inset of Fig. 4(a). The rising (field on) and falling (field off) times of the responses were found to be about 8.5 ms and 27.5 ms, respectively, meaning that the switching times are fast enough for video-rate applications.


Power generating reflective-type liquid crystal displays using a reflective polariser and a polymer solar cell.

Ho Huh Y, Park B - Sci Rep (2015)

Voltage-dependent reflectance (blue curves) and short-circuit photocurrent density (red curves) characteristics of the reflective-type Solar-LCD in the normal white (a) and black (b) modes under green (upper), blue (middle), and red (lower) illumination.The inset in (a) shows the temporal responses of reflectance from the Solar-LCD with a 2.0 V square-wave voltage applied.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477406&req=5

f4: Voltage-dependent reflectance (blue curves) and short-circuit photocurrent density (red curves) characteristics of the reflective-type Solar-LCD in the normal white (a) and black (b) modes under green (upper), blue (middle), and red (lower) illumination.The inset in (a) shows the temporal responses of reflectance from the Solar-LCD with a 2.0 V square-wave voltage applied.
Mentions: Next, in order to investigate the dual functionality of the reflective-type Solar-LCD, consisting of the GBO reflecting polariser between the TN-LC cell and the isotropic PCDTBT:PCBM70 PSC, we measured its electro-optical characteristics (Fig. 4). Figure 4(a) shows the reflectance characteristics of the reflected output from the device as a function of the voltage applied (Vapp) to the TN-LC cell in the NW mode under B(442 nm), G(532 nm), and R(633 nm) light. Here, the absolute reflectance is denoted by R0 for zero voltage and becomes saturated with increasing Vapp; the applied voltage that produces a relative brightness of 90% is termed the threshold voltage Vth, and the applied voltage that produces a relative brightness of 10% is termed the saturation voltage Vsa. The application of any voltage over Vth to the TN-LC cell causes the LC molecule to become vertically aligned. It can be seen (Fig. 4(a)) that in the voltage-off state (low voltage), the incident linearly polarised light passing through the front polariser changes its polarisation such that it is perpendicular to the front polariser following propagation through the TN-LC cell, and the light then reflects from the rear GBO polariser and passes again through the TN-LC cell and the front polariser. The reflectance is therefore high (R0 ~ 13–15%), representing the bright reflection state for Vapp < Vth (0.75 V). Moreover, when the voltage applied to the TN-LC cell Vapp > Vth, the effective birefringence and retardation value decrease to zero, and the amount of reflected light decreases, resulting in light absorption by the bottom PSC. The results of the measurements were: Vth = 0.70 V, Vsa = 1.10 V, R0 = 15.1% (for G), and the absolute reflectance at Vsa was 0.9%. Therefore, the contrast ratio of the intensity of bright to dark (IBRIGHT/IDARK) increases, reaching a maximum value of ca. 18.1, 18.1, and 17.5, for R, G, and B light, respectively, i.e., over a wide range of wavelengths of incident light. This contrast ratio clearly increases at high voltages, and the threshold voltage for the bright state is only about 0.75 V, which makes it suitable for a variety of applications, although the contrast ratio value at a given voltage differs slightly for each colour due to the variation in the phase retardation of the TN-LC cell. At the same time, we also assessed the power-generating abilities of the bottom PSC in terms of the short-circuit photocurrent from the Solar-LCD as a function of the voltage applied to the TN-LC cell in NW mode under B, G, and R light, as also shown in Fig. 4(a). Here it can clearly be seen that in the voltage-on state, the bottom PSC in the Solar-LCD generated an output photocurrent density Jsc of more than 0.40 mA/cm2 per unit of incident light power density (mW/cm2, green) for Vapp above Vsa (1.10 V), because incident light passed through the GBO reflecting polariser, whereas Jsc decreased markedly to 0.05 mA/cm2 when Vapp < 0.7 V. The measured response times are also shown in the inset of Fig. 4(a). The rising (field on) and falling (field off) times of the responses were found to be about 8.5 ms and 27.5 ms, respectively, meaning that the switching times are fast enough for video-rate applications.

Bottom Line: We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD.The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17-19.We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrophysics, Kwangwoon Univ., Wolgye-Dong, Nowon-gu, Seoul 139-701, Korea.

ABSTRACT
We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD. The PSC consisted of a polymer bulk-heterojunction photovoltaic (PV) layer of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] and [6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PCBM70), and showed a high power conversion efficiency of about 5%. In order to improve the visibility of the Solar-LCD, between the TN-LC and the PV cells we inserted a reflective polariser of a giant birefringent optical (GBO) film. The reflectivity from the Solar-LCD was observed to be considerably increased by more than 13-15% under illumination by visible light. The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17-19. We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices.

No MeSH data available.