Perovskite Solar cells with Back Contact

1. Back-contacted hybrid organic–inorganic perovskite
solar cells
It is expected that a better cell performance as well as reduced J-V hysteresis can be achieved by
fabricating a perovskite layer with larger grains and better crystallinity, which will lead to a
longer diffusion length.
Askhat N. Jumabekov, Enrico Della
Gaspera, Zai‐Quan Xu
2016

2. Synopsis
This text is an accepted manuscript that has undergone peer review and will be published online before being edited and formatted.
The Royal Society of Chemistry is not responsible for any errors or omissions in the manuscript.
A group led by Askhat Jumabekov from the Soochow University (2016) reported in ‘Back-contacted hybrid organic–inorganic
perovskite solar cells’ that a back-contacted solid-state perovskite solar cell with charge selective electrodes was fabricated using
quasi-interdigitated electrodes (QIDEs).
The device demonstrated stable power output and could be illuminated from either the absorber or glass substrate side.
It was suggested that a smaller gap between the fingers of the QIDE could improve charge collection and increase photocurrent
collection efficiency.
The performance of the cell could be improved by fabricating a perovskite layer with larger grains and better crystallinity.
The selection of a hole selective layer material with a better band offset could also enhance performance.
The QIDE structure was found to be tolerant to defects and could potentially be used for large-scale production of perovskite solar
cells.
The maximum power conversion efficiency achieved with the novel cell architecture was over 6.0%.

3. Key concepts
• solar cell
• maximum power point
• indium tin oxide
• Accepted Manuscript
• transparent conducting oxide
• scanning electron microscopy
• Melbourne Centre for Nanofabrication
• Royal Society
• Australian National Fabrication Facility
• hysteresis
• technical editing
• graphics

4. Abstract
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been
accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting
and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we
publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is
available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical
editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms &
Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any
errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.

5. Confirms previous work
NiOx blocking the PL signal. Generally the photolVuiemwiAnrteicsleceOnnlcinee map has a very patchy appearance, an DoObIs:
e10rv.1a0t3i9o/nC6tThCa0t06is81iGn agreement with earlier observations by Ginger and coworkers.[22]

6. Builds on previous research
The high intrinsic defect tolerance of the QIDE structure and the effective doubling of the process resolution potentially makes the
electrode amenable to printing, allowing for it to be applied to the future large scale production of perovskite SCs. Although we
used photolithVoiewgrAartpichleyOnlitnoe demonstrate the proof of concept forDtOhIi:s10a.1r0c3h9it/Ce6cTtuCr0e0,68w1Ge
believe this structure can be also fabricated by cheap alternative methods such as reverse-offset printing, which can produce sub-
micron patterns.[29]

7. Differs from previous work
The applied bias changes will significantly change the magnitude of the local electric field within the perovskite layer close to this
junction, resulting in a significantly larger bias dependence in bottom illumination, compared to the top illumination mode.
Furthermore, we expect that the maximized local electric field close to the QIDE surface (at the boundary of the anode and
cathode) will decay quickly when moving away from the QIDE surface due to the high dielectric constant, εr, of the perovskite
(~70).[23,24,25,26] In addition, the perovskite layer has a very high extinction coefficient at the laser wavelength (532 nm) used
for photocurrent mapping

8. Highlights
• This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been
accepted for publication
• We demonstrated that the device produces a stable power output and can be illuminated from either the absorber or glass
substrate side
• This suggests that a smaller gap between the fingers of the quasi-interdigitated electrodes (QIDEs) could potentially improve
charge collection, resulting in a more homogenous and higher photocurrent collection efficiency
• It is expected that a better cell performance as well as reduced J-V hysteresis can be achieved by fabricating a perovskite layer
with larger grains and better crystallinity, which will lead to a longer diffusion length.[27,28]
• We concluded that an improved performance can be achieved by the careful selection of a hole selective layer (HSL) material
that can give a better band offset with the perovskite for a higher driving force for hole extraction
• The high intrinsic defect tolerance of the QIDE structure and the effective doubling of the process resolution potentially makes
the electrode amenable to printing, allowing for it to be applied to the future large scale production of perovskite solar cell (SC)

9. Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available to the community, in citable form, before we publish the edited
article.
Authors can make their results available to the community, in citable form, before we publish the edited article
We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the Information for Authors.
In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or
any consequences arising from the use of any information it contains

10. Journal of Materials Chemistry C COMMUNICATION
We use QIDEs to fabricate the first back-contacted solid-state perovskite solar cell with charge selective electrodes.
In the complete QIDE the two charge collecting electrodes (ITO and Al/Ni) are continuously covered and separated by oxide
layers, in which the ZnO layer acts as the ESL and the NiOx as the HSL (Fig. 2a(vi) and Fig. S2, ESI†).
The SEM image at lower magnification shows the 2 μm wide and ~200 nm thick fingers of the QIDE separated by a 2 μm gap on
the glass/ITO/ZnO substrate, and a ~500 nm thick CH3NH3PbI3 perovskite absorber layer on top.
For both sets of measurements the device was monitored using moderate forward (0.2 V), short-circuit (0 V) and reverse (−0.2V)
bias potentials.
In bottom illumination mode the charge carriers can be more effectively picked up by the electric field generated by the small
applied bias, compared to top illumination mode

11. Findings
The maximum PCE achieved with our novel cell architecture under standard AM 1.5 at 1 Sun illumination is over 6.0%.
We concluded that an improved performance can be achieved by the careful selection of a HSL material that can give a better band
offset with the perovskite for a higher driving force for hole extraction

12. Conclusions
We have shown a fabrication process for backcontacted perovskite SCs with a simple and novel architecture.
Characterization of the devices with PL and PC mapping techniques showed that the photocurrent collection is inhomogeneous
throughout the active area of the cell and is most efficient near the interface between the ESL and HSL.
This suggests that a smaller gap between the fingers of the QIDE could potentially improve charge collection, resulting in a more
homogenous and higher photocurrent collection efficiency.
The back-contact devices will be useful for conducting fundamental studies as it has an exposed photoactive area, permitting in situ
measurements on the effects of chemical treatment or passivation