Celdas de CdS/CdTe con diferentes capas ventana

Transcription

1 CENTRO DE INVESTIGACIÓN Y DE ESTUDIOS AVANZA DOS DEL IPN UNIDAD QUÉRETARO Celdas de CdS/CdTe con diferentes capas ventana Dr. Rafael Ramírez Bon LIFyCS, Temixco, Mor., Marzo 211

2 COLLABORATORS R. Ochoa Landín, UNISON Yuri Vorobiev, Cinvestav-Qro O. Vigil Galán ESFM-IPN

3 Thin film solar cells: CdTe-CdS and CIGS-CdS CdTe CIS/CIGS BACK CONTACT Graphite Mo ABSORBENT LAYER CdTe Cu(InGa)(SeS) 2 WINDOW LAYER CdS-i CdS-i TRANSPARENT ELECTRODE SnO 2 ZnO-n ++ Properties of the CdS window layers: 4-1 nm thickness High optical transmission

4 The sodium citrate-cadmium chloridethiourea, ammonia-free system CHARACTERISTICS OF THE AMMONIA-FREE CBD PROCESS: Substitution of ammonium salt by sodium citrate Variable concentrations of cadmium and sulfur ions ph control [Cd]/[thiourea]=.2 [Cd]/[citrate]=.1 T = 7 C Five samples sets, t = 15, 3, 6, 9 and 12 min Reactive (Conc.) M1 M2 M3 M4 CdCl 2 (.5 M) C 6 H 5 O 7 Na 3 (.5 M) KOH (.5 M) ph 1 borate buffer CS(NH 2 ) 2 (.5 M) [Cd] mg/ml

5 Intensity (Arb. units) Intensity (Arb. units) (2) (2) Structural properties 7 CdS M1 8 CdS M min 9 min min 9 min 3 6 min 3 6 min min 15 min Theta (Degrees) min 15 min Theta (Degrees) CdS hexagonal crystalline phase

6 Intensity (Arb. units) Intensity (Arb. units) (2) (2) Structural properties 6 CdS M3 CdS M min 12 min min 1 9 min min 3 min 5 6 min 3 min 15 min Theta (Degrees) 15 min Theta (Degrees) Highly oriented hexagonal polycrystalline films (2) preferred crystalline orientation

7 Intensity (Arb. Units) Intensity (Arb. Units) Grain size (nm) Crystallinity and lattice constant M1 M2 M3 M Deposition time (min) Amount of Cd (mg/ml) 1 M2 films have best crystalline properties

8 Intensity (Arb. Units) Lattice constant (A) Tunnable lattice constant 4 M M M M Amount of Cd (mg/ml) 2 Theta (Degrees) Residual stress causes different lattice constants

9 T, R (%) T, R (%) Optical properties CdS M2 15 min 3 min 6 min 9 min 12 min T R CdS M4 15 min 3 min 6 min 9 min 12 min T R Wavelength (nm) Wavelength (nm)

10 T, R (%) Physical system of CdS layer structure Roughness Substrate Air CdS ) M1 2) M2 3) M3 4) M4 Experimental Fit T R CdS compact layer modeled by a version of Lorents oscillator The roughness layer was modeled by the Bruggeman effective media approximation Wavelength (nm)

11 Thickness (nm) Lattice constant (A) Grain size (nm) Growth kinetics 15 M1 M2 M3 M Deposition time (min) Energy band gap (ev) Film thickness increases with Cd concentration Energy band gap depending on lattice constant

12 Application to CdS/CdTe solar cells CdS X 25 ml CdCl2;.1 M 2 ml C6H5O7Na3; 1 M 15 ml NH4OH; 4 M 1 ml CS(NH2)2; 1 M 3 ml H2O desionizada 7 C; 2 minutos Au-Cu CdS Y 1 ml CdCl2;.5 M 2 ml C6H5O7Na3;.5 M 5 ml KOH;.3 M 5 ml Buffer; ph=1 1 ml CS(NH2)2;.5 M 5 ml H2O desionizada 7 C; 6 minutos Au-Cu CdS Z 1 ml CdCl2;.5 M 2 ml C6H5O7Na3;.5 M 5 ml KOH;.3 M 1 ml CS(NH2)2;.5 M 5 ml H2O desionizada 7 C; 9 minutos Au-Cu ITO, 25 nm Au-Cu ITO, 25 nm Au-Cu ITO, 25 nm Au-Cu FTO, 5 nm FTO, 5 nm FTO, 5 nm

13 Intensidad (U. A.) The CdTe layer 1 mm 4 (111) Pelicula de CdTe (22) 1 (311) 5 Las películas de CdTe se crecieron con la técnica de sublimación en espacio cercano (CSVT), la temperatura del substrato fue de 55 C y la de la fuente 65 C. El espesor de la película fue alrededor de 5 μm Theta (Grados)

14 CdS/CdTe solar cells Cu-Au, Ni CdS Cu-Au CdTe (5 mm) CdS (1 nm) ITO glass substrate

15 INTENSITY (ARB. UNITS) INTENSITY (ARB. UNITS) INTENSITY (ARB. UNITS) CdS/ITO and CdS/FTO XRD patterns 8 a) * * CdS ** ITO CdS Y FTO ITO 6 4 ** ** ** THETA (DEGREES) ** CdS Z 2 CdS Y 6 b) * * CdS CdS X SnO * * CdS Z + 2 CdS Y CdS X THETA (DEGREES)

16 T (%) T (%) CdS/ITO and CdS/FTO T spectra a) ) CdS X 2) CdS Y 3) CdS Z 4) ITO 2 1 ITO SUBSTRATES 9 8 b) ) CdS X 2) CdS Y 3) CdS Z 4) SnO 2 SnO 2 SUBSTRATES WAVELENGTH (nm)

17 CdS/ITO surface morphology CdS X 1.25 mm 1.5 µm CdS Y.25 mm 25. nm CdS Z.25 mm 25. nm 1 mm mm. µm 1 mm mm. nm 1 mm mm. nm

18 CdS/FTO surface morphology CdS X 1.75 mm 1.5 µm CdS Y 1.25 mm 1.5 µm CdS Z 1.25 mm 25. nm 1 mm mm. µm 1 mm mm. µm 1 mm mm. nm

19 CURRENT DENSITY (ma/cm 2 ) CURRENT DENSITY (ma/cm 2 ) CdS/CdTe solar cells parameters a) b) 2 3 1) CdS X 2) CdS Y 3) CdS Z ) CdS X 2) CdS Y 3) CdS Z 1 2 ITO SUBSTRATES 3 FTO SUBSTRATES Cells V oc (mv) J sc (ma/cm 2 ) FF (%) η (%) X/ ITO Y/ ITO Z/ ITO X/ FTO Y/ FTO Z/ FTO VOLTAGE (mv)

20 CdS/CdTe solar cells quantum efficiency QUANTUM EFICIENCY (%) QUANTUM EFICIENCY (%) a) ) X 2) Y 3) Z ITO SUBSTRATES 1 9 b) ) X 2) Y 3) Z FTO SUBSTRATES WAVELENGTH (nm)

21 Conclusions The sodium citrate-cadmium chloride-thiourea system is very Cu-Au, Ni convenient for the chemical deposition of CdS Highly oriented polycrystalline CdS films are obtained by means of this sytem CdS Some of the properties, including the layer microstructure, can be tunned by modifying the precursor concentrations The CdS films were used as window layers in CdTe solar cells