All our efforts to demonstrate a multifunctional device – photovoltaic gas sensor (i.e. solar cell which
show photovoltaic action depending on the gas / volatile organic compounds (VOC) in the surrounding
atmosphere) yielded negative results. Photovoltaic performance of the organic solar cells under study
degraded – almost permanently by exposing them to volatile organic compounds (VOCs). Although, the
proposed multifunctional device could not be demonstrated; Present investigations yielded very important
result that organic solar cells have problems not only with oxygen and humidity (known facts) but also
with many VOCs and hazardous gases – making lamination / encapsulation step mandatory for their practical
utilizatio

Somani, Prakash R.

Somani, Savita P.

Umeno, Masayoshi

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 6 No 4, 04010(2pp) (2014) Том 6 № 4, 04010(2cc) (2014) 
 
 
2077-6772/2014/6(4)04010(2) 04010-1  2014 Sumy State University 
Volatile Organic Compounds are Ghosts for Organic Solar Cells 
 
Prakash R. Somani1,2,*, Savita P. Somani1,2, Masayoshi Umeno2 
 
1 Applied Science Innovations Pvt. Ltd., Pune – 411041 Maharashtra, India  
2 Chubu University, Kasugai-shi, Aichi-Ken, Japan 
 
(Received 15 August 2014; published online 29 November 2014) 
 
All our efforts to demonstrate a multifunctional device – photovoltaic gas sensor (i.e. solar cell which 
show photovoltaic action depending on the gas / volatile organic compounds (VOC) in the surrounding  
atmosphere) yielded negative results. Photovoltaic performance of the organic solar cells under study  
degraded – almost permanently by exposing them to volatile organic compounds (VOCs). Although, the 
proposed multifunctional device could not be demonstrated; Present investigations yielded very important 
result that organic solar cells have problems not only with oxygen and humidity (known facts) but also 
with many VOCs and hazardous gases – making lamination / encapsulation step mandatory for their prac-
tical utilization. 
 
Keywords: Organic solar cell, Lamination, Volatile organic compounds. 
 
 PACS numbers: 82.47.Jk, 42.79.Ek 
 
 
                                                 
* psomani1@yahoo.com 
Recently, we demonstrated a multifunctional device 
by combining photovoltaic action and pressure sensing 
i.e. Pressure dependent photovoltaic action [1]. The 
device can be used as a solar cell, a pressure sensor or a 
photovoltaic pressure sensor. Motivated by this, we 
started with a novel idea of demonstrating a multifunc-
tional device – Photovoltaic Gas Sensor – which is pro-
posed to show photovoltaic action depending on the 
analyte in the surrounding atmosphere – and which 
can be used as a solar cell, as a gas sensor or a photo-
voltaic gas sensor. The ‘analyte’ can be either volatile 
organic compounds (VOCs) or hazardous gases. Hetero-
junction devices, n-Si / P3OT (incorporated with either 
double walled carbon nanotubes or multiwalled carbon 
nanotubes) are exposed to VOCs and their photovoltaic 
performance is measured. All my efforts yielded nega-
tive results irrespective of the type of the gas (electron 
donor or acceptor). Photovoltaic performance of the 
solar cells degraded – almost permanently. We could 
not realize the proposed multifunctional device; howev-
er, present investigations yielded very important re-
sults that organic solar cells have problems not only 
with oxygen and humidity (known facts) but with all (at 
least many) kinds of VOCs and hazardous gases – mak-
ing the lamination / encapsulation step mandatory for 
their practical utilization. 
Carbon nanotubes (CN) are attracting interest for 
application in photovoltaic energy conversion devices  
[2-12]. Incorporation of CN in organic / organic-
inorganic heterojunction solar cells is shown to improve 
the device performance by many folds [2-12]. In the 
present study, we used the same device which we have 
reported earlier in references [11, 12]. Double walled 
carbon nanotubes (DWCN) were incorporated in the 
polymeric layer of the n-Si / regioregular Poly(3-
octylthiophene) (P3OT) heterojunction solar cell. The 
device structure is n-Si / P3OT + DWCN / Au. Cell is 
illuminated from the semi-transparent Au (25 nm) side 
whereas n-Si makes a direct electrical contact with the 
conducting stainless steel stage. Thickness of the 
P3OT + DWCN layer was approximately 900 nm. Cur-
rent-voltage (I-V) characteristics were measured in 
dark and under AM 1.5 simulated solar radiation at 
room temperature (25 C) using a JASCO SS-200 W 
solar simulator. Current-Voltage (I-V) characteristics 
measured in air are taken as reference. Cells were also 
exposed to the saturated vapor (s) of the analyte and 
the I-V characteristics of such cells in dark and under 
illumination were recorded. Solar cells were soaked 
considerably (10 min.) in the saturated vapor of the 
analyte before taking the I-V measurements. After 
measurement of the photovoltaic performance in pres-
ence of analyte gas / vapor, the cells were exposed to air 
and the I-V measurements were recorded after every 
fixed pre-determined interval of time so as to under-
stand recovery process. New solar cell is used every 
time for every analyte separately. Solar cells were also 
fabricated incorporating the multi-walled carbon nano-
tubes in the polymer layer of n-Si / P3OT heterojunc-
tion solar cells (Cell configuration: n-
Si/MWCN+P3OT/Au) and tested in the similar manner. 
Vapors of ethanol, isopropyl alcohol (IPA), toluene are 
used as analytes. 
Typical as prepared n-Si / P3OT heterojunction so-
lar cell containing DWCN (n-Si / P3OT + DWCN / Au) 
shows (in air) the open circuit voltage (Voc), short-
circuit current density (Isc), fill factor and white light 
conversion efficiency of approximately 0.53 V, 
5.9 mA/cm2, 0.15 and 0.49 %, respectively. This perfor-
mance (in air) is considered as a reference value. I-V 
curve in dark goes through origin and shows rectifica-
tion. After exposing such device to saturated vapor of 
isopropyl alcohol (IPA), the performance of the device 
decreases and becomes steady. Such device under illu-
mination shows Voc, Isc, FF and %  approximately as 
0.3935 V, 0.2689 mA/cm2, 0.1726 and 0.018 %, respec-
tively. The response time (time taken by the device to 
saturate at its performance after exposed to analyte) is 
observed to be approximately 7 min whereas the recov-
ery is almost absent. In fact, the device did not recov-
 P.R. SOMANI, S.P. SOMANI, M. UMENO J. NANO- ELECTRON. PHYS. 6, 04010 (2014) 
 
 
04010-2 
ered its performance at all even after 48 hours in air 
atmosphere indicating thereby that it has undergone 
irrecoverable damage. Fast response and recovery is 
usually required for sensor applications. Long response 
time (in mins) observed which might be due to the fact 
that top surface (P3OT + DWCN) of the device is cov-
ered by the gold electrode (but not completely) whereas 
silicon is present at the bottom surface which prevents 
analyte molecules to interact with the active organic 
material (i.e. P3OT + DWCN film). We believe that in 
the present device, P3OT and DWCN are mainly the 
sensing materials and the interaction of volatile organ-
ic molecules with them should be considered. Hence, 
interaction and diffusion of IPA molecules inside the 
P3OT + DWCN film occurs mainly through the side 
edges of the device which are not protected. Further, 
the IPA molecules should diffuse throughout the film 
volume so as to saturate the performance of the device. 
Hence, it was expected that such device will show long-
er response times. Similar is the case for recovery of 
the device. Original performance of the device could 
only be achieved if all the IPA molecules somehow come 
out of the device – leaving the device microstructure 
intact. The only space through which they can come out 
of the active materials (P3OT + DWCN) film is again 
the side edges of the device. Hence, the smaller area of 
the side edges results in longer response and recovery 
time for the device. Nevertheless, the solar cell changes 
(more specifically, decreases) in its photovoltaic per-
formance when exposed to the vapor of volatile organic 
compound, IPA. Similar decrease of the photovoltaic 
performance is also observed when the device is ex-
posed to vapors of other volatile organic compounds 
such as ethanol and toluene. It is to be noted here that 
IPA and ethanol are polar organic compounds whereas 
toluene is a non-polar organic compound. Similar effect 
(decrease in the photovoltaic performance when ex-
posed to the vapors of volatile organic compounds) is 
also observed in the devices incorporating MWCN  
(device structure : n-Si / MWCN + P3OT / Au). We be-
lieve that the irrecoverable damage to the device per-
formance is due to the destruction of the organic active 
layer microstructure. Even annealing the devices in air 
/ in nitrogen could not recover their performance. 
In conclusion, we started with a novel idea of 
demonstrating a multifunctional device – Photovoltaic 
Gas Sensor – which can act as a gas sensor, a solar cell 
or a photovoltaic gas sensor. However, we got only 
negative results that the photovoltaic performance of 
the heterojunction solar cells i.e. n-Si / P3OT (contain-
ing DWCN or MWCN) decreases by exposing these 
devices to the vapors of volatile organic compounds. 
Type of the gas / vapor (polar / non-polar; electron-
donating / accepting) seems to be irrelevant and only 
decreases the photovoltaic performance of the organic 
solar cells. The irrecoverable, almost permanent dam-
age to the device performance might be due to destruc-
tion of the device microstructure and internal connect-
ing / percolating paths for transfer of charge carriers to 
respective electrodes. However, present investigations 
yielded very important result that organic solar cells 
have problem not only with oxygen and humidity but 
also with all / many kinds of VOCs and hazardous gas-
es – making lamination / encapsulation step almost 
mandatory for their practical utilization. 
 
Table 1 – Solar cell performance in air and when exposed to different VOC vapors. 
 
Solar Cell Structure: n-Si / P3OT + DWCN / Au 
Sr. No.  Description Voc (V) Isc (mA/cm2) FF %  
1 Reference (in air) 0.53 5.9 0.15 0.49 
2 Ethanol 0.4642 0.4423 0.1763 0.0362 
3 Isopropyl Alcohol 0.3935 0.2689 0.1726 0.0182 
4 Toluene 0.3656 0.2149 0.1702 0.0133 
 
 
 
REFERENCES 
 
1. P.R. Somani, Appl. Phys. Lett. 96, 173504 (2010).  
2. H. Ago, K. Petritsch, M.S.P. Shaffer, A.H. Windle, 
R. H. Friend, Adv. Mater. 11, 1281 (1999).  
3. H. Ago, M.S.P. Shaffer, D.S. Ginger, A.H. Windle, 
R.H. Friend, Phys. Rev. B 61, 2286 (2000). 
4. E. Kymakis, G.A.J. Amaratunga, Appl. Phys. Lett. 80, 112 
(2002). 
5. E. Kymakis, I. Alexandrou, G.A.J. Amaratunga, J. Appl. 
Phys. 93, 1764 (2003). 
6. B.J. Landi, R.P. Raffaelle, S.L. Castro, S.G. Bailey, Prog. 
Photovolt.: Res. Appl. 13, 165 (2005).  
7. R. Ulbricht, X. Jiang, S. Lee, et. al., phys. status solidi b 
243, 3528 (2006). 
8. M.W. Rowell, M.A. Topinka, M.D. McGehee, H.J. Prall, 
G. Dennler, N.S. Sariciftci, L. Hu, G. Gruner, Appl. Phys. 
Lett. 88, 233506 (2006). 
9. A.J. Miller, R.A. Hatton, S.R.P. Silva, Appl. Phys. Lett. 89, 
133117 (2006). 
10. T.M. Barnes, X. Wu, J. Zhou, A. Duta, J.V.D. Lagemaat, 
T.J. Coutts, C.L. Weeks, D.A. Britz, P. Glatkowski, Appl. 
Phys. Lett. 90, 243503 (2007). 
11. S.P. Somani, P.R. Somani, E. Flahaut, M. Umeno, Appl. 
Phys. Lett. 89, 223505 (2006). 
12. P.R. Somani, S.P. Somani, E. Flahaut, M. Umeno, Nano-
technology 18, 185708 (2007). 
 


English

Volatile organic compounds are ghosts for organic solar cells

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 6 No 4, 04010(2pp) (2014) Том 6 № 4, 04010(2cc) (2014)   2077-6772/2014/6(4)04010(2) 04010-1  2014 Sumy State University Volatile Organic Compounds are Ghosts for Organic Solar Cells  Prakash R. Somani1,2,*, Savita P. Somani1,2, Masayoshi Umeno2  1 Applied Science Innovations Pvt. Ltd., Pune – 411041 Maharashtra, India  2 Chubu University, Kasugai-shi, Aichi-Ken, Japan  (Received 15 August 2014; published online 29 November 2014)  All our efforts to demonstrate a multifunctional device – photovoltaic gas sensor (i.e. solar cell which show photovoltaic action depending on the gas / volatile organic compounds (VOC) in the surrounding  atmosphere) yielded negative results. Photovoltaic performance of the organic solar cells under study  degraded – almost permanently by exposing them to volatile organic compounds (VOCs). Although, the proposed multifunctional device could not be demonstrated; Present investigations yielded very important result that organic solar cells have problems not only with oxygen and humidity (known facts) but also with many VOCs and hazardous gases – making lamination / encapsulation step mandatory for their prac-tical utilization.  Keywords: Organic solar cell, Lamination, Volatile organic compounds.   PACS numbers: 82.47.Jk, 42.79.Ek                                                    * psomani1@yahoo.com Recently, we demonstrated a multifunctional device by combining photovoltaic action and pressure sensing i.e. Pressure dependent photovoltaic action [1]. The device can be used as a solar cell, a pressure sensor or a photovoltaic pressure sensor. Motivated by this, we started with a novel idea of demonstrating a multifunc-tional device – Photovoltaic Gas Sensor – which is pro-posed to show photovoltaic action depending on the analyte in the surrounding atmosphere – and which can be used as a solar cell, as a gas sensor or a photo-voltaic gas sensor. The ‘analyte’ can be either volatile organic compounds (VOCs) or hazardous gases. Hetero-junction devices, n-Si / P3OT (incorporated with either double walled carbon nanotubes or multiwalled carbon nanotubes) are exposed to VOCs and their photovoltaic performance is measured. All my efforts yielded nega-tive results irrespective of the type of the gas (electron donor or acceptor). Photovoltaic performance of the solar cells degraded – almost permanently. We could not realize the proposed multifunctional device; howev-er, present investigations yielded very important re-sults that organic solar cells have problems not only with oxygen and humidity (known facts) but with all (at least many) kinds of VOCs and hazardous gases – mak-ing the lamination / encapsulation step mandatory for their practical utilization. Carbon nanotubes (CN) are attracting interest for application in photovoltaic energy conversion devices  [2-12]. Incorporation of CN in organic / organic-inorganic heterojunction solar cells is shown to improve the device performance by many folds [2-12]. In the present study, we used the same device which we have reported earlier in references [11, 12]. Double walled carbon nanotubes (DWCN) were incorporated in the polymeric layer of the n-Si / regioregular Poly(3-octylthiophene) (P3OT) heterojunction solar cell. The device structure is n-Si / P3OT + DWCN / Au. Cell is illuminated from the semi-transparent Au (25 nm) side whereas n-Si makes a direct electrical contact with the conducting stainless steel stage. Thickness of the P3OT + DWCN layer was approximately 900 nm. Cur-rent-voltage (I-V) characteristics were measured in dark and under AM 1.5 simulated solar radiation at room temperature (25 C) using a JASCO SS-200 W solar simulator. Current-Voltage (I-V) characteristics measured in air are taken as reference. Cells were also exposed to the saturated vapor (s) of the analyte and the I-V characteristics of such cells in dark and under illumination were recorded. Solar cells were soaked considerably (10 min.) in the saturated vapor of the analyte before taking the I-V measurements. After measurement of the photovoltaic performance in pres-ence of analyte gas / vapor, the cells were exposed to air and the I-V measurements were recorded after every fixed pre-determined interval of time so as to under-stand recovery process. New solar cell is used every time for every analyte separately. Solar cells were also fabricated incorporating the multi-walled carbon nano-tubes in the polymer layer of n-Si / P3OT heterojunc-tion solar cells (Cell configuration: n-Si/MWCN+P3OT/Au) and tested in the similar manner. Vapors of ethanol, isopropyl alcohol (IPA), toluene are used as analytes. Typical as prepared n-Si / P3OT heterojunction so-lar cell containing DWCN (n-Si / P3OT + DWCN / Au) shows (in air) the open circuit voltage (Voc), short-circuit current density (Isc), fill factor and white light conversion efficiency of approximately 0.53 V, 5.9 mA/cm2, 0.15 and 0.49 %, respectively. This perfor-mance (in air) is considered as a reference value. I-V curve in dark goes through origin and shows rectifica-tion. After exposing such device to saturated vapor of isopropyl alcohol (IPA), the performance of the device decreases and becomes steady. Such device under illu-mination shows Voc, Isc, FF and %  approximately as 0.3935 V, 0.2689 mA/cm2, 0.1726 and 0.018 %, respec-tively. The response time (time taken by the device to saturate at its performance after exposed to analyte) is observed to be approximately 7 min whereas the recov-ery is almost absent. In fact, the device did not recov- P.R. SOMANI, S.P. SOMANI, M. UMENO J. NANO- ELECTRON. PHYS. 6, 04010 (2014)   04010-2 ered its performance at all even after 48 hours in air atmosphere indicating thereby that it has undergone irrecoverable damage. Fast response and recovery is usually required for sensor applications. Long response time (in mins) observed which might be due to the fact that top surface (P3OT + DWCN) of the device is cov-ered by the gold electrode (but not completely) whereas silicon is present at the bottom surface which prevents analyte molecules to interact with the active organic material (i.e. P3OT + DWCN film). We believe that in the present device, P3OT and DWCN are mainly the sensing materials and the interaction of volatile organ-ic molecules with them should be considered. Hence, interaction and diffusion of IPA molecules inside the P3OT + DWCN film occurs mainly through the side edges of the device which are not protected. Further, the IPA molecules should diffuse throughout the film volume so as to saturate the performance of the device. Hence, it was expected that such device will show long-er response times. Similar is the case for recovery of the device. Original performance of the device could only be achieved if all the IPA molecules somehow come out of the device – leaving the device microstructure intact. The only space through which they can come out of the active materials (P3OT + DWCN) film is again the side edges of the device. Hence, the smaller area of the side edges results in longer response and recovery time for the device. Nevertheless, the solar cell changes (more specifically, decreases) in its photovoltaic per-formance when exposed to the vapor of volatile organic compound, IPA. Similar decrease of the photovoltaic performance is also observed when the device is ex-posed to vapors of other volatile organic compounds such as ethanol and toluene. It is to be noted here that IPA and ethanol are polar organic compounds whereas toluene is a non-polar organic compound. Similar effect (decrease in the photovoltaic performance when ex-posed to the vapors of volatile organic compounds) is also observed in the devices incorporating MWCN  (device structure : n-Si / MWCN + P3OT / Au). We be-lieve that the irrecoverable damage to the device per-formance is due to the destruction of the organic active layer microstructure. Even annealing the devices in air / in nitrogen could not recover their performance. In conclusion, we started with a novel idea of demonstrating a multifunctional device – Photovoltaic Gas Sensor – which can act as a gas sensor, a solar cell or a photovoltaic gas sensor. However, we got only negative results that the photovoltaic performance of the heterojunction solar cells i.e. n-Si / P3OT (contain-ing DWCN or MWCN) decreases by exposing these devices to the vapors of volatile organic compounds. Type of the gas / vapor (polar / non-polar; electron-donating / accepting) seems to be irrelevant and only decreases the photovoltaic performance of the organic solar cells. The irrecoverable, almost permanent dam-age to the device performance might be due to destruc-tion of the device microstructure and internal connect-ing / percolating paths for transfer of charge carriers to respective electrodes. However, present investigations yielded very important result that organic solar cells have problem not only with oxygen and humidity but also with all / many kinds of VOCs and hazardous gas-es – making lamination / encapsulation step almost mandatory for their practical utilization.  Table 1 – Solar cell performance in air and when exposed to different VOC vapors.  Solar Cell Structure: n-Si / P3OT + DWCN / Au Sr. No.  Description Voc (V) Isc (mA/cm2) FF %  1 Reference (in air) 0.53 5.9 0.15 0.49 2 Ethanol 0.4642 0.4423 0.1763 0.0362 3 Isopropyl Alcohol 0.3935 0.2689 0.1726 0.0182 4 Toluene 0.3656 0.2149 0.1702 0.0133    REFERENCES  1. P.R. Somani, Appl. Phys. Lett. 96, 173504 (2010).  2. H. Ago, K. Petritsch, M.S.P. Shaffer, A.H. Windle, R. H. Friend, Adv. Mater. 11, 1281 (1999).  3. H. Ago, M.S.P. Shaffer, D.S. Ginger, A.H. Windle, R.H. Friend, Phys. Rev. B 61, 2286 (2000). 4. E. Kymakis, G.A.J. Amaratunga, Appl. Phys. Lett. 80, 112 (2002). 5. E. Kymakis, I. Alexandrou, G.A.J. Amaratunga, J. Appl. Phys. 93, 1764 (2003). 6. B.J. Landi, R.P. Raffaelle, S.L. Castro, S.G. Bailey, Prog. Photovolt.: Res. Appl. 13, 165 (2005).  7. R. Ulbricht, X. Jiang, S. Lee, et. al., phys. status solidi b 243, 3528 (2006). 8. M.W. Rowell, M.A. Topinka, M.D. McGehee, H.J. Prall, G. Dennler, N.S. Sariciftci, L. Hu, G. Gruner, Appl. Phys. Lett. 88, 233506 (2006). 9. A.J. Miller, R.A. Hatton, S.R.P. Silva, Appl. Phys. Lett. 89, 133117 (2006). 10. T.M. Barnes, X. Wu, J. Zhou, A. Duta, J.V.D. Lagemaat, T.J. Coutts, C.L. Weeks, D.A. Britz, P. Glatkowski, Appl. Phys. Lett. 90, 243503 (2007). 11. S.P. Somani, P.R. Somani, E. Flahaut, M. Umeno, Appl. Phys. Lett. 89, 223505 (2006). 12. P.R. Somani, S.P. Somani, E. Flahaut, M. Umeno, Nano-technology 18, 185708 (2007).  

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Volatile organic compounds are ghosts for organic solar cells

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SocioEconomic Challenges Journal (Sumy State University)

Electronic Sumy State University Institutional Repository