# Presentation: 671271

## Barrier Coatings and Effects of Moisture on SSI CIGSS Cells

**Larry Olsen, Sambu Kundu and Mark Gross**
** ****Pacific Northwest National Laboratory (PNNL)**

## Outline Of Presentation

**Introduction**
**Background**
**3.  Approach To Studies With SSI Circuits**
**4.  Results For Accelerated Tests**
**5.  Key Results / Future Work**

## PNNL Program :  Barrier Coatingsand Stability of Thin Film Solar Cells

_**PROGRAM**_
**Funded By NREL As Part of the ‘Thin Film Partnership’**
_**OBJECTIVE**_
** ****Develop Low Cost Barrier Coatings For Thin Film Solar Cells**
** ****Investigate Mechanisms Influencing Cell Stability**
_**APPROACH**_
_**Utilize Multilayer Coating Technology Developed at PNNL**_** For OLEDs to Coat Thin Film Cells Provided By Industry**
**Carry Out **_**Current-Voltage**_** and **_**Photoresponse**_** Analyses, **_**Physical**_** **_**Characterization**_** In Collaboration With NREL and **_**Modeling**_** to **_**Investigate Degradation Mechanisms**_** **

## Background

**PNNL Has Developed Multilayer Coatings For Organic LEDs**
**Multilayers Comprised Of   Alternating Polymer And Oxide Layers**
**Have Demonstrated Coatings On Glass Characterized By WVTR Values Less Than 2x10****-7**** g/m****2****/d**

**OLED**

**Multilayer**
**Coating**

**Glass**

**OLED Structure**

**Monomer**

**Cure**

**Ceramic**
**Deposition**

**WVTR (g/m****2****/d)**

## Basis For Multilayer Coating

_**Diffusion Rate Of Water**_** And Oxygen Through Homogeneous **_**Oxide Layers**_** Is Extremely Low**
_**Penetration Of Moisture**_** Or Oxygen Through Oxide Based  Coatings **_**Occurs Because Of Defects**_** In Oxide – Usually Due To Region Of Substrate **_**Protruding Through Coating   **_
**PNNL Approach:**
**	****-  Smoothing First Polymer Layer**
**	****-  Multilayer To Provide Tortuous**
**	****   ****Path For Water And Oxygen**

**H****2****O Through Defect**

**First Polymer**
**Smoothing Layer**

**Oxide Layer**

**Multilayer **
**Coating**

**Substrate**

**Substrate**

## Barrier Coatings For SSI Circuits

**PNNL Is Collaborating With SSI To Develop Barrier Coatings For SSI Circuits**
**           **
**SSI Provides 10 cm x 10 cm Circuits With Depleted Edge**
**Multilayer Coatings Applied As Illustrated With Relatively Thick First Polymer Layer**
**Coated Circuits Subjected To 60****o****C/90% RH For Accelerated Testing**

## Process Development

**Clean Circuits To Eliminate Debris**
**Nodules In CIGSS Is Key Issue**
**First Layer Adjusted To Achieve Effective Barrier**
**Initial Polymer Layer Thickness Was **_**0.5 **__**μ**__**m For Coating Shown In Micrographs**_
**Circuits Coated With First Layer Being 0.5 **_**μ**__**m Began To Degrade After 600 Hours**_

***5 ******μ******m Nodule***

***12 m Nodule***

**Potential **
**Pathway **

## Process Development

-  **Micrograph Is For Multilayer**
**    ****Coating  With Initial Polymer **
**    ****Layer Of 4 ****μ****m**
** ****Note The **_**Planarizing Effect **_
**    ****Of First Layer**
** ****Coatings With Initial Layer **
**    ****Of 4 ****μ****m Allow SSI Circuits**
**    ****To Survive 1000 Hours In**
**    ****60****oC/90RH Environment**

## Results For SSI Circuits

**Efficiency vs Hours At 60****o****C / 90% RH**

_**SSI Circuits With No Barrier**_** Coating Degrade Rapidly In a 60****o****C/90% RH Environment**
_**Developed An Approach**_** For Barrier Coating Deposition That Provides Significant Protection – Less Than 5% Decrease In Efficiency  After 1000 Hours Under  60/90 Conditions**
_**Thickness Of First Polymer Layer **_**For Results Shown Is As Follows:**
**	****-  Circuit  A --  No Barrier Coating**
**	****-  Circuit  B --  0.5 ****μ****m**
**	****-  Circuit  C --  4.0 ****μ****m                                    **
**        **
**  **

**C**

**B**

**A**

## Measurements By Shell Solar

**Two Coated Circuits Were Returned To SSI For Characterization**
**SSI Measured I-V As Received From PNNL, Then Subjected To UV For 10 Days And Tested Again**

**Circuit     I****sc**** (Amps)     V****oc ****(Volts)        FF       P****max ****(Watts)  Rel Change****	****	****	****	****	****	****      ****   **

**Bare Circuit         22 - 4           0.184            5.633            0.508           0.525**
**Coated Circuit     22 - 4           0.192            5.420            0.561           0.582           1.108       **
**(1000 hr @60/90)**
**After UV Test      22 - 4           0.183            5.275            0.515           0.498           0.856**
**Bare Circuit         22 - 9           0.180            5.652            0.581           0.592           **
**Coated Circuit     22 - 9           0.189            5.495            0.608           0.631           1.066**
**(1000 hr @ 60/90)**
**After UV Test      22 - 9           0.183            5.750            0.653           0.688           1.091**
**	**

## Measurements By Shell (Continued)

**Efficiency (%)**

**12**

**10**

**11**

**9**

**8**

**Circuit**

**Bare Circuit**

**Coated Circuit &**
**1000 Hrs @ 60/90**

**After 10 Days **
**      ****Of UV**

**22 -4**

**22 - 9**

## Effect Of Moisture On Bare SSI Circuit 

**mA/cm****2**

**Hrs @ 60/90**

**Hrs @ 60/90**

**Hrs @ 60/90**

**Hrs @ 60/60**

## Effect Of Moisture On Bare SSI Circuit          Photoresponse And I-V Parameters

_**External Photoresponse**_
**Measurements for Small Cell **
**     ****Formed On Rectangular **
**     ****Region Cut From SSI Module**
_**Dark I-V Characteristics**_
**All of Average Cell **
**     ****Parameters  Degrade**

## Modifed Barrier Coating Structure

_**Current Approach    **_
**Multilayer Structure Consists Of: **
**Initial Polymer Layer /Al2O3**** **
**Plus 4 Pairs Of Polymer/Al2O3**
**      ****Layers**
_**Reduced Number Of Pairs**_
**Will Utilize Initial Layers, But**
**      ****Begin To Reduce Number Of Pairs**
**Early Results For Efficiency Of**
**      ****Circuit With **_**Three-Pair Coating**_
**	**** ****Given In Figure **

## Key Results

PNNL Multilayer Barrier Coating Developed That Effectively Protects SSI Circuits From Moisture in 60/90 Environment

Effects Of Moisture On Uncoated SSI Circuits Characterized

Future Work

Initiate Testing Of SSI Circuits at 85/85

Investigate Effects Of Multilayer Coatings With Reduced 
     Number of layers 

Correlate SSI Circuit With Estimated WVTR Values

Consider Studies of Other Types Of Cells

**PNNL Multilayer Barrier Coating Developed That Effectively Protects SSI Circuits From Moisture in 60/90 Environment**
**Effects Of Moisture On Uncoated SSI Circuits Characterized**
_**Future Work**_
**Initiate Testing Of SSI Circuits at 85/85**
**Investigate Effects Of Multilayer Coatings With Reduced **
**     ****Number of layers **
**Correlate SSI Circuit With Estimated WVTR Values**
**Consider Studies of Other Types Of Cells**