The innovation engine for new materials

Sarah Wang

2013 Intern


University of California, Santa Barbara


Chemical Engineering

Site Abroad: 

Oxford University, England


Darren Chi Neo
Vincent Tobin

Faculty Sponsor(s): 

Hazel Assender

Faculty Sponsor's Department: 


Project Title: 

Degradation of encapsulated PbS nanocrystal photovoltaic devices with a flexible barrier layer

Project Description: 

Organic and inorganic hybrid photovoltaics offer advantages over purely inorganic, silicon based photovoltaics due to potential in flexibility and cheaper production. This would allow for industrial size roll-to-roll processing, decreasing the cost and time to fabricate commercially used solar cells. A major problem in photovoltaics is degradation, in which device performance significantly decreases when exposed to oxygen and air in the atmosphere. There are many possible factors in degradation, such as chemical or morphological; this project will mainly observe the overall degradation over time due to the atmosphere such as light, water, and oxygen exposure. Lead sulfide, PbS, nanocrystals (synthesized by Chi Neo) were used to make devices which were encapsulated with a transparent, flexible aluminium oxide and polymer barrier layer (fabricated by Vincent Tobin) or glass held together by degassed epoxy. An optical calcium test was used to show the penetration of water and oxygen through the epoxy layer is minimal and is not the limiting factor. The results showed that devices encapsulated with a barrier layer worked better over time than non-encapsulated devices. The device with no barrier layer tended to perform better the first day, but degrade quickly, while the encapsulated devices tended to degrade slower but start off with a lower efficiency. The encapsulated devices also showed slight increases in efficiency after the first day, speculated to be due to doping with oxygen. The devices that were stored with exposure to light did not perform as well as the devices stored in darkness. But this may also be due to the temperature the lamp emitted, annealing the devices. Comparing the barrier layers, glass barrier layer showed less degradation than the aluminium oxide barrier layer, since glass is expected to have no water or oxygen penetration. The aluminium oxide barrier showed to perform better than no barrier at all, which gives us hope for a flexible device that could be encapsulated from water and oxygen degradation.