Preparation of cigs absorber layers using coated semiconductor nanoparticle and nanowire networks

Abstract

We disclose a method of preparing CIGS absorber layers using coated semiconductor nanoparticle and nanowire networks. The nanoparticles and nanowires containing one or more elements from group IB and/or IIIA and/or VIA are prepared from metal salts such as metal chloride and acetate at room temperature without inert gas protection. A uniform and non-aggregation CIGS precursor layer is fabricated with the formation of nanoparticle and nanowire networks utilizing ultrasonic spraying technique. High quality CIGS film is obtained by cleaning the residue salts and carbon agents at an increased temperature and selenizing the pretreated precursor layer.

What is claimed is: 
     
         1 . A method of preparing a CIGS absorber layer by using a metal salt, a thickening agent, and a binding agent to form uniform nanoparticle and nanowire networks and to finish a high quality CIGS film after selenization comprising the steps of:
 a) producing CIGS nanoparticles and nanowires based on using a metal salt at room temperature without inert gas protection;   b) coating a CIGS precursor layer on a Mo glass substrate;   c) generating uniform nanoparticle and nanowire networks by initial heat treatment;   d) obtaining a clean CIGS precursor layer by cleaning residue salts and carbon agents at an increased temperature above 200° C.; and   e) fabricating high quality CIGS film after selenizing the pretreated precursor layer at a temperature above 400° C.   
     
     
         2 . A method as defined in  claim 1 , wherein the metal salt used to produce said nanoparticles and nanowires is at least one of a metal chloride and a metal acetate. 
     
     
         3 . A method as defined in  claim 1 , wherein said glass substrate is coated by ultrasonic spraying of said nanoparticles and nanowires solution. 
     
     
         4 . A method of preparing a CIGS-based solar cell comprising the steps of:
 synthesizing the soluble CuInGaS 2  nanoparticles/wires precursor at room temperature under non-vacuum condition;   preparing a CIGS-based ink, adding CIGS powder into specific solvent and adding additives to form monodispersed CIGS ink;   ultrasonic spraying CIGS ink on Mo glass substrate, using ultrasonic spray to reduce the aggregation effect of CIGS nanoparticles/wires and obtaining uniform CIGS precursor films;   heat treating of the CIGS precursor films to melt soluble CIGS nanopowder and change it to a clear solution, and cooling the solution to dry to a uniform and black color CIGS precursor film;   selenizing the heat treated CIGS precursor films, using Se powder as the Se-source and, creating high quality CIGS films after selenizing the precursor films in a double zone furnace for one approximately hour; and   preparing a CIGS device by chemical bath deposition and sputtering and evaporating step.   
     
     
         5 . A method as defined in  claim 4 , wherein said step of synthesizing CIGS nanoparticles/wires comprises the steps of:
 (a) providing a solution comprising Cu, In and Ga ions, the ratio of Cu, In and Ga being in the following proportions: Cu 0.9˜1; In 0.6˜0.8 and Ga 0.4˜0.2;   (b) providing a thickening solution;   (c) providing a sulfurated precipitant;   (d) providing an effective coupling agent;   (e) adding the solution comprising Cu, In and Ga ions into said thickening solution and stirring the mixture to form a homogeneous solution; and   (f) sequentially adding appropriate amounts of sulfurated precipitant and coupling agent into above homogeneous solution and stirring the mixture to form CuInGaS 2  nanoparticles/nanowires in a well dispersed solution.   
     
     
         6 . A method as defined in  claim 4 , wherein said step of preparing the CIGS-based ink comprises the steps of:
 (a) separating the CIGS nanoparticles/wires by centrifuging method;   (b) washing and drying the centrifuged CIGS nanoparticles/wires under vacuum pump and low temperature;   (c) providing the high volatilizing solvent with low boiling point;   (d) providing a small amount of additives, such as dispersants and thickening agents; and   (e) weighing an appropriate amount of CIGS solid powder, adding into the organic solvent and some additives, stirring for overnight to form a uniform ink.   
     
     
         7 . A method as defined in  claim 4 , wherein said step of ultrasonic spraying CIGS ink on Mo glass substrate comprises the steps of:
 (a) providing a Mo-coated glass substrate;   (b) providing monodisperse CIGS ink; and   (c) automatically ultrasonically spraying the CIGS ink onto the Mo-glass a plurality of times under 300° C.   
     
     
         8 . A method as defined in  claim 7 , wherein said CIGS ink is sprayed less than five times onto the Mo-glass. 
     
     
         9 . A method as defined in  claim 4 , wherein said selenizing step comprises the steps of:
 (a) providing pre-treated CIGS precursor films; and   (b) selenizing the hot-treated precursor films at a temperature above 500° C. for approximately 60 minutes in a selenization furnace using Selenium powder as the Se-source to obtain high-quality CIGS absorb layer.   
     
     
         10 . A method as defined in  claim 4 , wherein said step of preparing said CIGS device comprises the steps of:
 (a) depositing a buffer layer of CdS employing CBD method;   (b) sputtering a window layer of i-ZnO and a conductive AZO layer; and   (c) evaporating Ni/Al top-electrode to form a CIGS PV device with structure of glass/Mo/CIGS/CdS/i-ZnO/AZO/Ni—Al.   
     
     
         11 . A method as defined in  claim 4 , wherein said step of synthesizing CIGS nanoparticles/wires based solution comprises the steps of:
 (a) synthesizing a CuInGa precursor solution A by: Adding CuCl 2 .2H 2 O, InCl 3  and GaCl 3  into Methanol, stirring for up to 30 min and a green color solution is obtained;   (b) synthesizing a thickening solution B by: Adding EC into Terpinol, stirring overnight and heating up to a temperature of 200° C. until it is completely dissolved;   (c) mixing solution A and thickening agent solution B, and stirring for up to 5 hours; and   (d) gradually adding Thiourea and 3-MPA into the mixture of solution A and B to obtain a white nanoparticles-based solution.   
     
     
         12 . A method as defined in  claim 4 , wherein said step of preparing the CIGS-based ink comprises the steps of:
 (a) separating the CIGS nanoparticles/wires by methanol using centrifuging method up to five times;   (b) drying the centrifuged powder under vacuum pump under 100° C. for less than ten hours to obtain white color dried powder;   (c) weighing the CIGS dried powder, adding MEK as the solvent and PEG as the thickening agent and SHMP as the dispersant, then mixing together and stirring overnight to form CIGS ink.   
     
     
         13 . A method as defined in  claim 4 , wherein the procedure of ultrasonic spraying CIGS ink comprises the steps of:
 (a) providing a clean Mo-coated glass substrate, using acetone, ethanol and DI water to wash the Mo-glass successively, finally using N2 to blow to dry;   (b) providing monodispersed CIGS ink and storing in a container, extracting ink for ultrasonic spraying under following conditions or parameters:   running power of ultrasonic generator: P=less than 15 W;   temperature of the Mo-glass substrate: Ts=under 300° C.;   spraying rate: V=greater than 1 ml/min;   pressure of gas flow: P=greater than 5 Psi;   distance between the nozzle and the Mo-glass substrate: less than 150 mm;   number of sprays: n=less than 5 times;   whereby CIGS ink is ultrasonically sprayed onto the Mo-glass under 300° C. for less than five times, aggregation effect is reduced to obtain uniform and non-aggregated CIGS precursor films.   
     
     
         14 . A method as defined in  claim 4 , wherein said heat treatments step comprises:
 (a) heating the CIGS nanoparticles/nanowires coated substrate up to 350° C. to fuse all the particles to become a clear solution;   (b) heating the sample up to 450° C. gradually solidify the solution and the color changes from clear to red, and finally becomes deep black and the networks are formed through the decomposed nanowires; and   (c) increasing the temperature up to 500° C. and holding the temperature for half an hour to remove all the organic solvents and additives to finally cause the color to change to deep black.   
     
     
         15 . A method as defined in  claim 4 , wherein said step of selenization comprises the steps of:
 (a) using selenium powder as the solid-state Se-source and placing same in a graphite box, and then into a quartz tube of a selenization furnace at a low temperature zone; and   (b) placing the sample in a high temperature zone of the selenization furnace, and then using a mixture of Ar or N as the protection gas and Selenizing the hot-treated precursor films above 500° C. for 30-70 mins in a selenization furnace to form a high-quality CIGS absorber layer.   
     
     
         16 . A method as defined in  claim 4 , wherein said step of fabricating comprises the steps of:
 (a) preparing a CdS buffer layer through a chemical bath deposition (CBD) method;   (b) using CdSO 4  and Thiourea, adding NH 3 H 2 O and DI water, stirring and dissolving completely;   (c) placing the sample into a solution and heating up to 100° C. for up to 30 mins and removing the sample and using DI water flushing for removing the aggregated CdS particles and drying in an oven below 100° C. for 60-180 minutes;   (d) sputtering i-ZnO and AZO window layers,   (e) the sputtering depositing parameters of ZnO being as follows: sputtering power: P=100-200 W; sputtering pressure: P=0.5-10 mTorr; Ar/O 2 =5:1-2:1 gas flow=10-100 sccm; sputtering time: T=up to 20 minutes;   (f) sputtering depositing parameters of AZO being as follows: sputtering power: P=100-200 W; sputte 00 sccm; sputtering time: T=up to 30 minutes;   (g) evaporating Ni—Al electrode: and   (h) loading Ni wire and Al wire, placing the sample with mask covered on a heating stainless steel plate and sequencially evaporating Ni and Al wires under high vacuum background to create a CIGS device.