Reliable and Damage-Free Estimation of Resistivity of ZnO Thin Films for Photovoltaic Applications Using Photoluminescence Technique

N Poornima,T V Vimalkumar,V G Rajeshmon,C Sudha Kartha,K P Vijayakumar

doi:10.1155/2013/105796

N Poornima, T V Vimalkumar + Show 3 more

Open Access

https://doi.org/10.1155/2013/105796

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Abstract

This work projects photoluminescence (PL) as an alternative technique to estimate the order of resistivity of zinc oxide (ZnO) thin films. ZnO thin films, deposited using chemical spray pyrolysis (CSP) by varying the deposition parameters like solvent, spray rate, pH of precursor, and so forth, have been used for this study. Variation in the deposition conditions has tremendous impact on the luminescence properties as well as resistivity. Two emissions could be recorded for all samples—the near band edge emission (NBE) at 380 nm and the deep level emission (DLE) at ~500 nm which are competing in nature. It is observed that the ratio of intensities of DLE to NBE (/) can be reduced by controlling oxygen incorporation in the sample. - measurements indicate that restricting oxygen incorporation reduces resistivity considerably. Variation of / and resistivity for samples prepared under different deposition conditions is similar in nature. / was always less than resistivity by an order for all samples. Thus from PL measurements alone, the order of resistivity of the samples can be estimated.

Highlights

Extensive research is being promoted on zinc oxide (ZnO) owing to the unique optoelectronic properties such as wide band gap of 3.3 eV, large room-temperature exciton binding energy of 60 meV, and piezoelectricity [1,2,3,4,5]
The wide band gap makes it an excellent candidate for use in UV sensors [6], light emitting diodes [7, 8], solar cells [9,10,11], and so forth. It serves its purpose as antireflection coating in solar cells [12] and nanorod layers of ZnO can be coupled with compound semiconductor absorber layers as in extremely thin absorber (ETA) cells [13,14,15] or can be used in organic photovoltaics [16, 17]
The graph has been plotted on a log scale so that the variation can be clearly understood. It can be seen from the graph that the minimum value for both IDLE/INBE and resistivity is for sample of ZI-v and the variation of the two parameters is similar

Summary

Introduction

Extensive research is being promoted on ZnO owing to the unique optoelectronic properties such as wide band gap of 3.3 eV, large room-temperature exciton binding energy of 60 meV, and piezoelectricity [1,2,3,4,5]. The wide band gap makes it an excellent candidate for use in UV sensors [6], light emitting diodes [7, 8], solar cells [9,10,11], and so forth It serves its purpose as antireflection coating in solar cells [12] and nanorod layers of ZnO can be coupled with compound semiconductor absorber layers as in extremely thin absorber (ETA) cells [13,14,15] or can be used in organic photovoltaics [16, 17]. Films with good optical quality are required on a large scale This is where costeffective deposition techniques as wet chemical methods and spray pyrolysis play a vital role [36, 37]. Thin films of ZnO were deposited by spraying alcoholic solution of zinc salt and various parameters such as spray rate, solvent used, pH of solution, and dopants used were varied; its effect on PL spectrum and resistivity was analyzed. In order to substantiate our findings that PL can be used to analyze the resistivity of ZnO thin films, we have included our own similar observations with indium sulphide (In2S3) thin films

Experimental Technique

Results and Discussion

Effect of Variation of Deposition Parameters

Pristine

Conclusion