CdS/CdTe Heterostructures for Applications in Ultra-Thin Solar Cells.

Karla Gutierrez Z-B,José Andraca-Adame,Jorge Sastré-Hernández,Luis Moreno-Ruiz,Osvaldo De Melo,Hugo Martínez-Gutiérrez,Patricia G Zayas-Bazán,Salvador Gallardo,Gerardo Contreras-Puente,Francisco De Moure-Flores

doi:10.3390/ma11101788

Karla Gutierrez Z-B, José Andraca-Adame + Show 8 more

Open Access

https://doi.org/10.3390/ma11101788

Copy DOI

Abstract

The preparation of ultra-thin semi-transparent solar cells with potential applications in windows or transparent roofs entails several challenges due to the very small thickness of the layers involved. In particular, problems related to undesired inter-diffusion or inhomogeneities originated by incomplete coverage of the growing surfaces must be prevented. In this paper, undoped SnO2, CdS, and CdTe thin films with thickness suitable for use in ultra-thin solar cells were deposited with a radiofrequency (RF) magnetron sputtering technique onto conductive glass. Preparation conditions were found for depositing the individual layers with good surface coverage, absence of pin holes and with a relatively small growth rate adapted for the control of very small thickness. After a careful growth calibration procedure, heterostructured solar cells devices were fabricated. The influence of an additional undoped SnO2 buffer layer deposited between the conductive glass and the CdS window was studied. The incorporation of this layer led to an enhancement of both short circuit current and open circuit voltage (by 19 and 32%, respectively) without appreciable changes of other parameters. After the analysis of the cell parameters extracted from the current-voltage (I-V) curves, possible origins of these effects were found to be: Passivation effects of the SnO2/CdS interface, blocking of impurities diffusion or improvement of the band alignment.

Highlights

With an expected efficiency above 20% [1], conventional, highly absorbing, and non-transparentCdS/CdTe thin film solar cells are among the most promising photovoltaic devices for terrestrial purposes
Since the insertion of buffer layers has proven to increase the efficiency and the reproducibility of thick solar cells [6], we studied the influence of an undoped SnO2 (u-SnO2 ) buffer layer in the performance of our UT cells. u-SnO2 layers have been previously prepared by different techniques such as chemical reactive evaporation [7], chemical vapor deposition [8] or sputtering [9] as per our knowledge, there are no reports on the use of these buffer layers in UT solar cells
With the final objective of inserting them in the heterostructures, we proceeded to characterize the individual layers in terms of their morphology, crystalline structure, and chemical composition

Summary

Introduction

With an expected efficiency above 20% [1], conventional, highly absorbing, and non-transparentCdS/CdTe thin film solar cells are among the most promising photovoltaic devices for terrestrial purposes. The use of partially transparent CdS/CdTe ultra-thin (UT) solar cells has been the focus of recent research efforts due to the feasibility of their application in different kinds of windows or roofs [5] For these applications, UT cells should entail: (i) Efficiencies as high as possible (taking into account that a significant part of the radiation is obviously not absorbed in the cell); (ii) aesthetics, as to be compatible with building, sunroofs, etc.; (iii) adequate optical properties in the visible region as demanded by standard regulations tinted windows; and (iv) comfortable indoor buildings environment. These cells are fabricated with the absorber layer whose thickness is thinner than the length of optical absorption and carrier diffusion leading to the desired partial transparency and enhanced carrier collection

Methods

Findings

Discussion

Conclusion