Dominating Energy Losses in NiO p‐Type Dye‐Sensitized Solar Cells

Abstract

have been reported for n-type DSCs and further improvements should be feasible by pairing an n-type DSC with a p-type DSC to form a double junction tandem device. [ 4 ] A proof of concept experiment has demonstrated that this can be achieved by simply assembling a photocathode with a photoanode in a sandwich device sharing the same electrolyte. [ 5 ] Current matching of the photocathode to the photoanode was found to be essential for higher tandem DSC effi ciencies. These results have sparked further interest in p-DSC research, continuously improving the effi ciency of the best performing p-type DSC to currently 1.3%. [ 6 ] There is no intrinsic reason as to why a p-type DSC cannot be as effi cient as its n-type counterpart; however, the comparatively small choice of materials with suitable properties is an issue and much optimization will be necessary to reduce the effi ciency gap between the two devices. While reasonable photocurrents and photovoltages can be achieved, low fi ll factors (FFs) of ≈0.4 are generally limiting the device performance. [ 6 ] The FF is defi ned as the ratio of the electrical power output at the maximum power point ( P MP ) to the product of the short-circuit current ( I SC ) and the open-circuit voltage ( V OC ) and is often described as a measure of the "rectangularity" of the current voltage characteristic (JV curve) (see Equation ( 1) The peak light-harvesting effi ciency decreases from 63% at short circuit to 57% at 600 mV reducing the FF of NiO DSCs by 5%. This effect is expected to be more pronounced for future devices with higher operating voltages. Incident, photon-to-electron conversion effi ciency front-back analysis at applied bias is utilized to characterize the interfacial charge recombination. It is found that the recombination between the injected hole and the redox mediator has a surprisingly small effect on the FF.

Developments in and prospects for photocathodic and tandem dye-sensitized solar cells

“…As has been discussed both here and elsewhere [208,209], one of the major limitations of using NiO is its strong colouration. This is the chief limitation in the realisation of higher IPCE values [28,176] and another major reason, along with VB edge potential, why researchers have investigated a range of alternative p-type semiconductors.…”

“…SQ) shows radiative recombination to be a significant loss mechanism under ambient conditions. While it is neglected in this analysis, obviously it will play a role in reality, as shown by Daeneke et al [208] under applied bias. Radiative recombination in wide bandgap materials (such as TiO2, NiO) is expected to be small compared to what would be expected from the absorber material.…”

“…More recently, an extensive investigation published by Daeneke et al [208] identified several other limitations in addition to the issues raised above. should also be viewed in the light that our previous work with current matched photoelectrodes resulted in FFpn > FFn, FFp [28], suggesting that the fill factor in a tandem device is again a more complex issue.…”

Indium tin oxide as a semiconductor material in efficient p-type dye-sensitized solar cells

“…Electrochemically platinized electrodes were prepared following the literature procedures. 28 Measurements were conducted at short circuit conditions (presented in Figure 5) following procedures detailed elsewhere. 28 Inert electrolyte measurements were collected utilizing a three electrode spectro-electrochemical setup while applying the respective electrolyte rest potential to emulate short circuit conditions.…”

“…28 Measurements were conducted at short circuit conditions (presented in Figure 5) following procedures detailed elsewhere. 28 Inert electrolyte measurements were collected utilizing a three electrode spectro-electrochemical setup while applying the respective electrolyte rest potential to emulate short circuit conditions. TA spectroscopy was carried out on two custom-built spectrometers, one that was optimized for nanosecond and the other optimized for microsecond measurements.…”