KEYWORDS: Perovskite, Ultraviolet radiation, Solar cells, Titanium, Carrier dynamics, Absorption, Oxygen, Heterojunctions, Diffusion, Electron transport
In this study, the microscopic carrier dynamics that govern the UV stability of perovskite solar cells was investigated using pump-probe spectroscopy. In conventional perovskite solar cells, the UV-active oxygen vacancy in compact TiO2 prohibits current generation after UV degradation. On the other hand, the dominant vacancy type in 2D Ti1-xO2 atomic sheet transporting layer (ASTL) is a titanium vacancy, not UV-sensitive. Consequently, the carrier recombination are suppressed and further extends UV stability in perovskite solar cells with a 2D Ti1-xO2 ASTL. The dynamics of electron diffusion, electron injection, and hot hole transfer processes are found to be less sensitive to the UV irradiation. The ultrafast time-resolved data shown here clearly represent a close correlation between the carrier dynamics and UV aging of perovskite, thus providing insight into the origin of UV-induced degradation in perovskite solar cells.
The solar-powered LED lighting system has been commercialized for a long time. The system usually consists
of a DC to DC converter in order to convert the battery voltage into a fixed voltage or current for the LED lighting
luminaire. This will cause energy loss and system reliability due to the failure of DC/DC converter. In the present study,
we develop a special technique to drive the LED luminaire directly from battery utilizing PWM technique in order to
remove the DC/DC converter. However, instantaneous current overdriven can occur easily due to the variation of
battery voltage with the state-of-charge of battery.
In the present study, we setup a thermal chamber with temperature variation to within 40±3°C. A LED luminaire
was specially designed for the LED reliability test with four different circuits with each circuit connecting three LED
lamps serially. A driver is designed to provide 4 kinds of power inputs to LED: (a) 350mA constant current, (b)
700mA,100Hz, duty cycle=50%, (c)700mA, 10K Hz duty cycle=50% and (d) 1050mA, 100Hz, duty cycle=33%. The
tests were performed simultaneously to compare light decay between normal drive condition (a) and other PWM
driving conditions (b, c, d). The accumulated total test time so far is more then 7,032 hours and has shown no
significant light decay in 4 different loops. This reveals that the PWM technique directly driven by battery is feasible
and is able to reduce energy loss of DC to DC converter in the solar lighting system.
In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene)/TiO2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO2 nanorods surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 2.2 % under simulated A.M. 1.5 illumination (100mW/cm2) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.
The solution processable poly(3-hexylthiophene)(P3HT)/TiO2-nanorod hybrid material for solar cells has been
successfully demonstrated. A critical issue for using hybrid heterojunction concept is the interface properties which
affect the exciton separation efficiency and bi-carrier transport. To improve the interface properties, we replace the
insulating surfactant on TiO2 nanorod surface with a more conductive oligomer, carboxylate terminated 3-hexylthiophene (P3HT-COOH). The enhancement of exciton separation efficiency due to better organic-inorganic
interfacial compatibility can be obtained. The electron mobility for transporting in the TiO2 network is improved. A
power conversion efficiency has been increased 3 times by using this new hybrid material without optimization as
compared with the hybrid without P3HT-COOH modification.
This paper aims to propose a 3D nanostructured organic-inorganic hybrid photovoltaic device based on the ZnO
nanostructures/poly(3-hexylthiophene)(P3HT):TiO2 nanorods hybrids by solution processes at low temperature. An array
of ZnO nanorods with a larger size of ~50 nm in diameter and ~180 nm in length are grown to provide direct pathways
for efficient charge collection. TiO2 nanorods with a size of ~5 nm in diameter and ~20-30 nm in length are incorporated
into polymer to facilitate charge separation and transport by providing increased interfacial area and more effective
transport pathway. The device performance with the inclusion of TiO2 nanorods exhibits a seven times increase in the
short circuit current with respect to that without TiO2 nanorods.
Photovoltaic devices based on the conjugated polymer (poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene)
(MEH-PPV) / TiO2 nanorods hybrid materials are investigated. It is found that efficient charge separation occurs at the
interfaces of MEH-PPV/ TiO2 nanorods, accompanying with a significant quench in the photoluminescence (PL)
intensity and a decrease of PL lifetime with increasing TiO2 nanorod concentrations. The device based on the MEHPPV/
TiO2 nanorod hybrid material shows power efficiency about 2.2% at the incident light with a wavelength of 565
nm. The transport properties of the solar cells are further investigated and discussed.
The mechanisms of exciton dissociation and migration in the conjugated polymer
(poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene)(MEH-PPV) / CdSe nanoparticle
hybrid materials were investigated by steady-state and time-resolved photoluminescence spectroscopy.
Rapid exciton dissociation at the nanoparticle/polymer interfaces leading to quenching of the
photoluminescence efficiency
η and shortening of the measured lifetime τPL is observed. The excitons
which contribute to the remaining luminescence in polymer will migrate to the lower energy sites with
longer conjugated sequences in the composites. The result is evident from the observations of a redshift
of the photoluminescence peak positions, a progressive decrease of the Huang-Rhys factor S and an
increase in the nature radiative lifetime τR with increasing CdSe nanoparticle content. The solar cell
based on the MEH-PPV / CdSe nanoparticle hybrid materials are fabricated and the transport
mechanism of the device will also be discussed.
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