Stability and Photovoltaic Performance Studies of Bulk Heterojunction Polymer Solar Cells
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Date
2017-02
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Addis Ababa Universty
Abstract
This dissertation reports a research done on the stability and photovoltaic performance
studies of bulk heterojunction polymer solar cells. Different techniques were used, in order
to study the stability and performance of polymer solar cells fabricated using different
polymers and fullerenes.
Two fullerene derivatives with different electron affinity were used to fabricate polymer
solar cell based on P3HT as donor. Results obtained from UV-visible, FTIR and J-V
measurement showed that the P3HT:PCBM film and solar cells fabricated from
P3HT:PCBM as active layer have much better air stability than those made from
P3HT:ICBA as active layer. Due to lower electron affinity of ICBA, the blend of
P3HT:ICBA photobleached at a faster rate compared to PCBM.
Effect of sol-gel synthesized TiOx layer on the stability and performance of P3HT:ICBA
based solar cells were investigated by spectroscopic and electrical measurement methods.
Results from J-V measurements indicates that P3HT:ICBA/TiOx solar cell has better
performance and stability compared to the reference device. The higher value of shortcircuit
current density and open-circuit voltage for P3HT:ICBA/TiOx solar cell indicate the
role of TiOx layer as the optical spacer and hole blocking layer, respectively. The results
from UV-visible absorbance, J-V and C-V measurement on light irradiated
P3HT:ICBA/TiOx solar cell demonstrates that TiOx layer can be used to protect
P3HT:ICBA active layer from oxygen and water attack under ambient air and to improve
the working lifetime of P3HT:ICBA based device.
Investigation on the effect of two fullerene derivatives with similar electron affinity on the
photovoltaic performance and stability of P3HT based solar cells is presented. From UVvisible
measurements it is found out that P3HT mixed with both PC61BM and PC71BM has good ambient air photochemical stability. However, device based on P3HT:PC61BM has
better stability compared to P3HT:PC71BM based device.
The impact of two different fullerenes with similar electron affinity on the photovoltaic
performance and stability of PCDTBT based solar cells were studied. Results from UVvisible
absorbance indicate that unlike that of pure film of PCDTBT, blend of PCDTBT
with PC61BM, PC71BM and 1:1 mixture of PC61BM and PC71BM has relatively constant
absorbance under light exposure. The results show the stabilizing power of acceptor
fullerenes when mixed with PCDTBT. The results from J-V measurement indicates that the
solar cells made from PCDTBT:PC61BM and PCDTBT:PC61+71BM have better stability
under light exposure in ambient air compared to the device based on PCDTBT:PC71BM.
When only PC71BM is used as acceptor the device has higher rate of decay of PCE.
The effect of DIM on the PCE and stability of PSCs made of PCDTBT:PC71BM is
investigated. PCE of the device based on PCDTBT:PC71BM processed with DIM is higher
than the reference device. In terms of device stability, the PSCs processed with DIM
showed poor stability at longer light exposure time. For the device without DIM especially
as the light exposure time was increased, the device stability was better. The result from IS
measurement shows that for pristine PCDTBT:PC71BM devices with DIM, the active layer
resistance is lower compared to device without DIM. However, after irradiating the device
for 5 hr the resistance of the device processed with DIM is higher and it is consistent with
decreased PCE of aged device.
The investigation presented on the application of NIL for performance improvement of
organic solar cells shows that, NIL is really promising technique for improving efficiency
of polymer solar cells. Nanopatterning of the PEDOT:PSS electrode can be used as a way
to improve the cell efficiency. In our case relative increase of the 60%, from 0.8% to 1.3%
of efficiency is obtained. The increased interfacial area and higher hole collection
contributed for the improved photovoltaic performance of nanopatterned device.
Keywords: polymer solar cells, degradation, photochemical stability, lifetime, charge
carrier mobility, P3HT, PCDTBT, ICBA, PC61BM, PC71BM, TiOx, DIM, nanopatterning
Description
Keywords
polymer solar cells; degradation; photochemical stability; lifetime; charge carrier mobility; P3HT; PCDTBT; ICBA, PC61BM; PC71BM; TiOx; DIM; nanopatterning