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Solar energy conversion using CdSe photoelectrochemical cells with low cost substrates
Solar Cells, 1 (1979/80) 367 - 370
367
© Elsevier Sequoia S.A., Lausanne -- Printed in the Netherlands
S O L A R E N E R G Y C O N V E R S I O N USING CdSe PHOTOELECTROCHEMICAL CELLS WITH LOW COST SUBSTRATES
SURESH CHANDRA
Department of Physics, Banaras Hindu University, Varanasi-22IO05, (India)
Uttar Pradesh
RAJENDRA K. PANDEY* and RAKESH (2. AGRAWAL* Department of Physics, Ravishankar University, Raipur, Madhya Pradesh (India) (Received July 19, 1979; accepted September 7, 1979)
Summary Photoelectrochemical cells using electrocodeposited CdSe films on low cost substrates (stainless steel and graphite) were studied. The usefulness of graphite as a counterelectrode in place of platinum was demonstrated. Results are reported for three cell configurations: stainless steel lCdSell electrolyte IIPt; stainless steel ICdSe [Ielectrolyte li C; C [CdSe [[electrolyte IIPt.
The study of photoelectrochemical processes at s e m i c o n d u c t o r electrolyte interfaces has recently become a very active field of research for solar energy conversion. A number of low band gap semiconductors have found application in the fabrication of photoelectrochemical cells (PECs) either to photoelectrolyse water or to obtain electricity b y using solar energy [ 1 - 5]. One o f the more promising semiconducting materials for PEC technology has been shown to be CdSe. CdSe films were deposited either b y anodic deposition or b y electrocodeposition. Although electrocodeposition is simpler, until recently electrocodeposited CdSe films could be prepared only on titanium substrates. The PECs employing a TijCdSe photoelectrode had the configuration TilCdSe ilelectrolyte IIPt. Economics precludes the use of titanium and platinum as substrate and metal counterelectrode respectively. A practical solar cell should obviously use less costly components without sacrificing efficiency. Recently we succeeded in depositing CdSe on a stainless steel substrate by electrocodeposition [ 6 ] . In this paper we report our results on PECs in which stainless steel or graphite was used as substrate. Graphite or platinum was used as the counterelectrode in the PECs that employed CdSe films on stainless steel. The *Present .address: Department of Physics, Faculty of Science, Banaras Hindu University, Varanasi-221005, India.
368
following three cell configurations were studied: cell I, stainless steel ICdSe ]l electrolyte ]iPt; cell II, stainless steel JCdSe li electrolyte []C; cell III, C ICdSe i] electrolyte i] Pt. The electrolysis cell used to deposit the CdSe films consisted of an aqueous acidic solution of CdSO4 and SeO2. Stainless steel or graphite was used as the substrate while a cadmium plate was employed as the source electrode to maintain the supply of Cd 2+ ions. No external source was therefore required to drive the electrolysis. The electrolyte was stirred continuously during electrolysis. The Cd 2÷ and S e 2+ ions present in the solution were simultaneously deposited on the substrate. Good CdSe films on stainless steel for application in a PEC are generally obtained when the SeO2 concentration is 5 - 10 mg per 50 ml of water and the electrolysis temperature is between 32 and 40 °C. The detailed optimization results will be published elsewhere [ 6]. The electrolysis current density was 3.6 mA cm-2. Films of CdSe on graphite substrates were obtained at room temperature at an electrolysis current density of 3.3 mA cm -2 and an SeO2 concentration of 5 mg per 50 ml of water. To fabricate a PEC, the CdSe film obtained was dipped in a cell consisting of aqueous 1 M NaOH, 1 M N a 2 S and 1 M S with either platinum or graphite as the counterelectrode. A 300 W tungsten lamp was used for illumination. The graphite counterelectrode was prepared by dipping a graphite plate in an aqueous solution of cobaltous nitrate which seemed to improve the performance of the graphite electrode in the electrolyte containing sulphide and polysulphide ions with the formation of CoS in the pores of the graphite plate. CoS has been reported to act as an electrocatalyst for the reduction of sulphur [ 5 ]. The current and cell voltage were recorded by varying a resistance across the external circuit. Figure 1 gives the current-voltage plots for three PECs, cell I, cell II and cell III. Cell I had an open-circuit voltage of 340 mV and a short-circuit current density of 2.5 mA cm-2. When the same film was used in a PEC with a graphite counterelectrode (cell II), the open-circuit voltage obtained was 310 mV and the short-circuit current density was 3.6 mA cm-2. Cell III had an open,circuit voltage of 200 mV and a short-circuit current density of 0.9 mA cm-2. Plots of the power o u t p u t as a function of current density for the three cell configurations are given in Fig. 2. The m a x i m u m derivable powers from the three cells were 0.24 mW c m - 2 , 0.42 mW c m - 2 and 0.06 mW c m - 2 on illumination with a 300 W tungsten lamp. The stainless steel iCdSe PECs have been shown to be comparable with TilCdSe cells [6]. It is obvious from Fig. 2 that the power o u t p u t from the stainless steel lCdSe I]electrolyte li C cell is better than the power o u t p u t from the stainless steellCdSe Helectrolyte ilPt configuration. Therefore we can conclude that the electrocodeposition m e t h o d can be used to obtain good stainless steellCdSe PECs. The cost of these PECs can be further minimized by replacing the platinum counterelectrode by a graphite counterelectrode without sacrificing the efficiency. As shown by cell III,
369
3.6
3.2 2.8
2.ol-
\
g.,,.°.I
\c,~s,/,t,.
"~.'v:'¢:'" \v,~ -,,.,. \ ~CELL I
\CELLZI
0.~
Ceil voltage
(mY)
~"
Fig. 1. Current-voltage plots for the three PECs: o, ceil I, stainless steel lCdSell electrolyte IIPt; u, cell II, stainless steel ICdSe Uelectrolyte IIC; A, cell I I I , C ICdSe Uelectrolyte IIPt.
0.44
0.36
~0.28 ,= ~0.20
£ 012
\
//
Current
-,,cd ~e~,t..
density (ma / cm2 )
Fig. 2. P10t,s o f t h e o u t p u t against t h e c u r r e n t f o r t h e t h r e e PECs.
graphite can also be used as a substrate for the CdSe films; however, much optimization has to be carried o u t before this cell can compete with the stainless steel [CdSe PEC.
370
References 1 2 3 4 5 6
A. Fujishima and K. Honda, Nature (London), 238 (1972) 37. A.J. Nozik, J. Cryst. Growth, 39 (1977) 200, and references cited therein. W. A. Gerrard and J. R. Owen, Mater. Res. Bull., 12 (1977) 677. G. Hodes, J. Manasseh and D. Cahen, Nature (London), 261 (1976) 403. G. Hodes, J. Manassen and D. Cahen, J. Appl. Electrochem., 7 (1977) 181. S. Chandra and R. K. Pandey, Phys. Status Solidi A, 59 (1980), in the press
367
© Elsevier Sequoia S.A., Lausanne -- Printed in the Netherlands
S O L A R E N E R G Y C O N V E R S I O N USING CdSe PHOTOELECTROCHEMICAL CELLS WITH LOW COST SUBSTRATES
SURESH CHANDRA
Department of Physics, Banaras Hindu University, Varanasi-22IO05, (India)
Uttar Pradesh
RAJENDRA K. PANDEY* and RAKESH (2. AGRAWAL* Department of Physics, Ravishankar University, Raipur, Madhya Pradesh (India) (Received July 19, 1979; accepted September 7, 1979)
Summary Photoelectrochemical cells using electrocodeposited CdSe films on low cost substrates (stainless steel and graphite) were studied. The usefulness of graphite as a counterelectrode in place of platinum was demonstrated. Results are reported for three cell configurations: stainless steel lCdSell electrolyte IIPt; stainless steel ICdSe [Ielectrolyte li C; C [CdSe [[electrolyte IIPt.
The study of photoelectrochemical processes at s e m i c o n d u c t o r electrolyte interfaces has recently become a very active field of research for solar energy conversion. A number of low band gap semiconductors have found application in the fabrication of photoelectrochemical cells (PECs) either to photoelectrolyse water or to obtain electricity b y using solar energy [ 1 - 5]. One o f the more promising semiconducting materials for PEC technology has been shown to be CdSe. CdSe films were deposited either b y anodic deposition or b y electrocodeposition. Although electrocodeposition is simpler, until recently electrocodeposited CdSe films could be prepared only on titanium substrates. The PECs employing a TijCdSe photoelectrode had the configuration TilCdSe ilelectrolyte IIPt. Economics precludes the use of titanium and platinum as substrate and metal counterelectrode respectively. A practical solar cell should obviously use less costly components without sacrificing efficiency. Recently we succeeded in depositing CdSe on a stainless steel substrate by electrocodeposition [ 6 ] . In this paper we report our results on PECs in which stainless steel or graphite was used as substrate. Graphite or platinum was used as the counterelectrode in the PECs that employed CdSe films on stainless steel. The *Present .address: Department of Physics, Faculty of Science, Banaras Hindu University, Varanasi-221005, India.
368
following three cell configurations were studied: cell I, stainless steel ICdSe ]l electrolyte ]iPt; cell II, stainless steel JCdSe li electrolyte []C; cell III, C ICdSe i] electrolyte i] Pt. The electrolysis cell used to deposit the CdSe films consisted of an aqueous acidic solution of CdSO4 and SeO2. Stainless steel or graphite was used as the substrate while a cadmium plate was employed as the source electrode to maintain the supply of Cd 2+ ions. No external source was therefore required to drive the electrolysis. The electrolyte was stirred continuously during electrolysis. The Cd 2÷ and S e 2+ ions present in the solution were simultaneously deposited on the substrate. Good CdSe films on stainless steel for application in a PEC are generally obtained when the SeO2 concentration is 5 - 10 mg per 50 ml of water and the electrolysis temperature is between 32 and 40 °C. The detailed optimization results will be published elsewhere [ 6]. The electrolysis current density was 3.6 mA cm-2. Films of CdSe on graphite substrates were obtained at room temperature at an electrolysis current density of 3.3 mA cm -2 and an SeO2 concentration of 5 mg per 50 ml of water. To fabricate a PEC, the CdSe film obtained was dipped in a cell consisting of aqueous 1 M NaOH, 1 M N a 2 S and 1 M S with either platinum or graphite as the counterelectrode. A 300 W tungsten lamp was used for illumination. The graphite counterelectrode was prepared by dipping a graphite plate in an aqueous solution of cobaltous nitrate which seemed to improve the performance of the graphite electrode in the electrolyte containing sulphide and polysulphide ions with the formation of CoS in the pores of the graphite plate. CoS has been reported to act as an electrocatalyst for the reduction of sulphur [ 5 ]. The current and cell voltage were recorded by varying a resistance across the external circuit. Figure 1 gives the current-voltage plots for three PECs, cell I, cell II and cell III. Cell I had an open-circuit voltage of 340 mV and a short-circuit current density of 2.5 mA cm-2. When the same film was used in a PEC with a graphite counterelectrode (cell II), the open-circuit voltage obtained was 310 mV and the short-circuit current density was 3.6 mA cm-2. Cell III had an open,circuit voltage of 200 mV and a short-circuit current density of 0.9 mA cm-2. Plots of the power o u t p u t as a function of current density for the three cell configurations are given in Fig. 2. The m a x i m u m derivable powers from the three cells were 0.24 mW c m - 2 , 0.42 mW c m - 2 and 0.06 mW c m - 2 on illumination with a 300 W tungsten lamp. The stainless steel iCdSe PECs have been shown to be comparable with TilCdSe cells [6]. It is obvious from Fig. 2 that the power o u t p u t from the stainless steel lCdSe I]electrolyte li C cell is better than the power o u t p u t from the stainless steellCdSe Helectrolyte ilPt configuration. Therefore we can conclude that the electrocodeposition m e t h o d can be used to obtain good stainless steellCdSe PECs. The cost of these PECs can be further minimized by replacing the platinum counterelectrode by a graphite counterelectrode without sacrificing the efficiency. As shown by cell III,
369
3.6
3.2 2.8
2.ol-
\
g.,,.°.I
\c,~s,/,t,.
"~.'v:'¢:'" \v,~ -,,.,. \ ~CELL I
\CELLZI
0.~
Ceil voltage
(mY)
~"
Fig. 1. Current-voltage plots for the three PECs: o, ceil I, stainless steel lCdSell electrolyte IIPt; u, cell II, stainless steel ICdSe Uelectrolyte IIC; A, cell I I I , C ICdSe Uelectrolyte IIPt.
0.44
0.36
~0.28 ,= ~0.20
£ 012
\
//
Current
-,,cd ~e~,t..
density (ma / cm2 )
Fig. 2. P10t,s o f t h e o u t p u t against t h e c u r r e n t f o r t h e t h r e e PECs.
graphite can also be used as a substrate for the CdSe films; however, much optimization has to be carried o u t before this cell can compete with the stainless steel [CdSe PEC.
370
References 1 2 3 4 5 6
A. Fujishima and K. Honda, Nature (London), 238 (1972) 37. A.J. Nozik, J. Cryst. Growth, 39 (1977) 200, and references cited therein. W. A. Gerrard and J. R. Owen, Mater. Res. Bull., 12 (1977) 677. G. Hodes, J. Manasseh and D. Cahen, Nature (London), 261 (1976) 403. G. Hodes, J. Manassen and D. Cahen, J. Appl. Electrochem., 7 (1977) 181. S. Chandra and R. K. Pandey, Phys. Status Solidi A, 59 (1980), in the press