Electron-beam-induced current at absorber back surfaces of Cu (In,Ga) Se2 thin-film solar cells

The following article appeared in Journal of Applied Physics 115.1 (2014): 014504 and may be found at http://scitation.aip.org/content/aip/journal/jap/115/1/10.1063/1.4858393The present work reports on investigations of the influence of the microstructure on electronic properties of Cu(In,Ga)Se2 (CIGSe) thin-film solar cells. For this purpose, ZnO/CdS/CIGSe stacks of these solar cells were lifted off the Mo-coated glass substrates. The exposed CIGSe backsides of these stacks were investigated by means of electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements as well as by electron backscattered diffraction (EBSD). EBIC and CL profiles across grain boundaries (GBs), which were identified by EBSD, do not show any significant changes at Σ3 GBs. Across non-Σ3 GBs, on the other hand, the CL signals exhibit local minima with varying peak values, while by means of EBIC, decreased and also increased short-circuit current values are measured. Overall, EBIC and CL signals change across non-Σ3 GBs always differently. This complex situation was found in various CIGSe thin films with different [Ga]/([In]+[Ga]) and [Cu]/([In]+[Ga]) ratios. A part of the EBIC profiles exhibiting reduced signals across non-Σ3 GBs can be approximated by a simple model based on diffusion of generated charge carriers to the GBs.This work was supported in part by the BMU projects comCIGS and comCIGSII. R.C. acknowledges financial support from Spanish MINECO within the program Ramon y Cajal (RYC-2011-08521)

New formulation of Copper Zinc Tin Sulfide compounds An Ink precursors route to printed photovoltaics

We report on the development of copper zinc tin chalcogenide compounds, especially kesterite Cu2ZnSn S,Se 4 CZTSSe that can be used for low cost solar cells using scalable inexpensive coating processes. For the formulation of copper zinc tin sulfur inks we developed a new method relying on binary and ternary chalcogenide nanoparticles as precursors. The chemical composition of the resulting absorber layers can be controlled by varying the ratio of the NP precursors in the ink. The ink was first coated at room temperature on Mo coated soda lime glass substrates. After soft heat treatment in air, the obtained precursor layers were subjected to further annealing process under Ar H2S or Ar Se atmosphere to allow solid state reaction of the precursors to form CZTS Se absorber layers. The morphology and phase formation were investigated with scanning electron microscopy and grazing incident X ray diffraction. The Raman spectroscopy was utilized to better identify all secondary phases. Solar cell formation is completed by chemical bath deposition of CdS buffer layer followed by sputtered i ZnO ZnO Al bi layers. Solar cells with efficiencies around 1.17 were achieve

Cu2ZnSn S, Se 4 thin film absorbers based on ZnS, SnS and Cu3SnS4 nanoparticle inks Enhanced solar cells performance by using a two step annealing process

In this paper, we present the fabrication of Cu2ZnSn S, Se 4 CZTSSe thin film absorbers by a four step solution process based on ZnS, SnS and Cu3SnS4 nanoparticle precursors and their application in thin film solar cells. The influence of ligand exchange process on the morphologies of the resulting CZTSSe thin films was studied. Ligand exchange with each sequential spun coat layers leads to cracking films which can be avoided by combining ligand exchanged and non ligand exchanged processes. Moreover, a two step annealing process yields the most homogeneous films. CZTSSe thin films consisting a large grain and fine nanoparticle grain layered structure was formed. The formation of layered structure for the absorbers was found to be due to the existence of high content of carbon left near the back contact and the out diffusion of Cu and Zn from the bottom layer to the surface layer. As a result, solar cell conversion efficiency was improved from 1.2 to 3.0 upon adoption a two step annealing process. Temperature dependent I V characteristic analysis reveals the dominant loss mechanism of the solar cells is the strong CZTSSe and CdS buffer interface recombinatio

Thin Film Solar Cell Absorber Cu2ZnSnS4 CZTS by Annealing of Monodisperse Kesterite Nanoparticle Precursors

Indium in chalcopyrite based solar cell absorbers can be substituted by zinc and tin forming Cu2ZnSn S,Se 4 CZTS CZTSe . Light to electricity conversion efficiencies of solar cell based on CZTSSe absorber have recently reached 9.6 , making it a competitive and more sustainable replacement for existing CdTe and Cu In,Ga Se2 CIGS thin film technologies. The approach to grow CZTS using metal co deposition of the Cu II Zn II Sn IV system followed by sulfurisation is very promising technique for large scale production. However the process suffers from the incomplete sulfurisation of the precursors, and requires the development of suitable rapid thermal processing technique for the formation of single CZTS phase similar to that of Cu chalcopyrite solar absorber. In this work we report on the synthesis of uniform monodisperse CZTS nanoparticles at the temperature below 300 C without the precipitation of secondary phases such as ZnS. The as synthesized CZTS nanoparticles characterized by high resolution transmission electron microscopy HR TEM exhibited highly crystalline structure with a size variation of 18.0 4.0 nm. The energy dispersive X ray analysis EDXA confirmed the presence of all elements with the atomi ratio of 43.3 S, 31.0 Cu, 14.9 Zn and 10.8 Sn. Thin films made from CZTS NPs are of kesterite structure which can be greatly improved by annealing in Se Ar atmospher

Inkjet Printed Cu2ZnSn S, Se 4 solar cells

Cu2ZnSn S, Se 4 based solar cells with total area 0.5 cm2 power conversion efficiency of 6.4 are demonstrated from thin film absorbers processed by inkjet printing technology of Cu Zn Sn S precursor ink followed by selenization. The device performance is limited by the low fill factor, which is due to the high series resistanc

Air stable solution processed Cu2ZnSn Sx,Se 1 x 4 thin film solar cells Influence of ink precursors and preparation process

ABSTRACTQuaternary semiconductors, Cu2ZnSnS4 and Cu2ZnSnSe4 which contain only earth-abundant elements, have been considered as the alternative absorber layers to Cu(In,Ga)Se2 (CIGS) for thin film solar cells although CIGS-based solar cells have achieved efficiencies over 20 %. In this work we report an air-stable route for preparation of Cu2ZnSn(Sx,Se(1-x))4 (CZTSSe) thin film absorbers by a solution process based on the binary and ternary chalcogenide nanoparticle precursors dispersed in organic solvents. The CZTSSe absorber layers were achieved by spin coating of the ink precursors followed by annealing under Ar/Se atmosphere at temperature up to 580°C. We have investigated the influence of the annealing temperature on the reduction or elimination of detrimental secondary phases. X-ray diffraction combined with Raman spectroscopy was utilized to better identify the secondary phases existing in the absorber layers. Solar cells were completed by chemical bath deposited CdS buffer layer followed by sputtered i-ZnO/ZnO: Al bi-layers and evaporated Ni/Al grids.</jats:p

Formation of a disorderd hetero junction by diffusion of Cu I from CuSCN into In2S3 layers a surface photovoltage study

Charge selective disordered hetero junctions were formed in evaporated In2S3 layers by diffusing at 200 amp; 8201; C CuI from a CuSCN source. The thicknesses of In2S3 layers and diffusion times were varied between 5 and 80 amp; 8201;nm and between 2 and 19 amp; 8201;min, respectively. In some cases CuSCN layers were etched back with pyridine. Spectral and time dependent surface photovoltage measurements were carried out in the capacitor arrangement. It was observed that a competing process of charge separation and relaxation was initiated together with the formation of the charge selective In2S3 In2S3 Cu hetero junctio

Formation of a heterojunction by electrophoretic deposition of CdTe CdSe nanoparticles from an exhaustible source

Fast and well controlled electrophoretic deposition of CdTe and CdSe nanoparticle CdTe np and CdSe np layers and nanoparticle layer systems from an exhaustible source has been demonstrated. Using a small volume of pyridine based nanoparticle suspensions with varying concentrations, these were completely drained of nanoparticles during deposition. Our proposed approach is well suited to a practical realization of engineering materials with different band gaps for various promising applications such as fabrication of nanodevices. The formation of a charge selective contact across the CdTe np CdSe np heterojunction was investigated by surface photovoltage methods and evidence of the separation of charge carriers at a CdTe CdSe np heterojunction in amp; 8208;between was demonstrate