CIS Solar Cell Backside Electrode Alkali Diffusion Control
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Solution Overview
Problem
Existing methods for manufacturing CIS-based thin film solar cells face challenges in achieving high photoelectric conversion efficiency and reproducibility, particularly due to difficulties in uniformly adding alkali elements to the p-type light absorbing layer without using soda lime glass, which has a low strain point and limited alkali supply, and in controlling Na concentration with external Na compounds.
Innovation Solution
A method involving the formation of a backside electrode layer with alternating layers of alkali metal-containing and alkali metal-free materials, such as Mo, using sputtering or evaporation, on a high strain point glass or non-alkali glass substrate, allowing for precise diffusion of alkali elements into the p-type light absorbing layer, thereby increasing the formation temperature and improving uniformity and reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soda lime glass is used as the glass substrate to supply Na to the p-type light absorbing layer, then photoelectric conversion efficiency is improved, but the glass substrate deforms at high temperatures (550°C or more)
Solution Approach 1:
A Mo layer containing 0.1-10 wt% Na is introduced as an intermediary between the high strain point glass substrate and the p-type light absorbing layer. This Mo layer serves as a Na reservoir that supplies Na to the light absorbing layer during formation, enabling high-temperature processing without substrate deformation while maintaining efficient Na supply.
Solution Approach 2:
The backside electrode layer is segmented into multiple layers: a first Mo layer containing Na and a second Mo layer free from Na. This segmentation allows precise control of Na diffusion into the p-type light absorbing layer while maintaining structural integrity at high temperatures.
2Temperature
If high strain point glass or non-alkali glass is used as the glass substrate to withstand high temperatures, then formation temperature can be increased, but the glass contains little or no alkali and cannot supply sufficient alkali to the p-type light absorbing layer
Solution Approach 1:
The Mo layer containing 0.1-10 wt% Na acts as an intermediary Na supply source, compensating for the lack of alkali in high strain point glass substrates. This enables high-temperature formation processes while ensuring sufficient Na is supplied to the p-type light absorbing layer for optimal photoelectric conversion efficiency.
3Manufacturing precision
If Na compound (such as NaF) is added from the outside to control Na concentration in the p-type light absorbing layer, then Na concentration can be controlled, but uniform addition and lot-to-lot reproducibility are difficult to achieve
Solution Approach 1:
Na is preliminarily incorporated into the Mo layer during the electrode formation process. This preliminary action ensures uniform Na distribution in the backside electrode layer before the p-type light absorbing layer is formed, enabling consistent and reproducible Na supply across different production batches.
Solution Approach 2:
The Na supply function is merged with the backside electrode layer by incorporating Na into the Mo layer. This integration ensures that Na is supplied uniformly and reproducibly along with the electrode formation process, eliminating the variability associated with external Na compound addition methods.
4Quantity of substance
If NaF is added to the p-type light absorbing layer by spraying, then Na can be added to the layer, but the diameters of the added particles are not uniform and uniform spraying is difficult
Solution Approach 1:
The Mo layer serves as an intermediary that provides uniform Na distribution through its inherent structure. This eliminates the need for particle spraying and the associated uniformity problems, as Na is released uniformly from the Mo layer during the p-type light absorbing layer formation process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of high-quality CIS-based thin film solar cells with enhanced photoelectric conversion efficiency and cost-effectiveness by allowing high-temperature processing and precise alkali addition, overcoming the limitations of soda lime glass and external Na compound methods.
Implementation Method 1
Na, which is an Ia group element, contained in the soda lime glass is diffused into the p-type light absorbing layer in the formation process of this layer
Implementation Method 2
forming a backside electrode layer with alternating layers of alkali metal-containing and alkali metal-free materials, such as Mo, using sputtering or evaporation
Implementation Method 3
forming a backside electrode layer with alternating layers of alkali metal-containing and alkali metal-free materials, such as Mo, using sputtering or evaporation
Data Source
AI summary
In order to manufacture a CIS-based thin film solar cell that can achieve high photoelectric conversion efficiency by adding an alkali element to a light absorbing layer easily and with good controllability, a backside electrode layer (2) is formed on a substrate (1). Then, a p-type CIS-based light absorbing layer (3) is formed on backside electrode layer (2), and then an n-type transparent and electroconductive film (5) is formed on this p-type CIS-based light absorbing layer (3). At this time, the backside electrode layer (2) is constituted by forming a first electrode layer (21) using a backside electrode material in which an alkali metal is mixed and, then forming a second electrode layer (22) using the backside electrode material that does not substantially contain the alkali metal.