Organic and inorganic materials are being widely used for development of semi-transparent solar cells that may be integrated in office buildings and replacement windows to enable harvesting of low-cost solar energy over wide surfaces.
Perovskite-based solar cells combine simple, low-cost deposition methods with high power conversion efficiencies (PCEs), making them exciting new candidates for low-cost solar energy.
Currently there has been no simple method to enable the production of hole-conductor-free perovskite solar cells which avoids the use of expensive organic/polymeric hole-transporting materials (HTM).
There is need for a low-cost method is that enables precise control the transparency of the cell and high power conversion efficiencies (PCEs) in order to maximize overall solar cell efficiency.
Simple deposition method for the fabrication of semi-transparent, hole-conductor-free perovskite-based solar cells.
(A) The PCE of the semi-transparent HTM free cells vs. their average transparency calculated in the range of 400–800 nm wavelengths.
(B) The average transparency of the perovskite solar cells vs. the concentration (%wt) of the assembly solution of the precursors.
(C) Images of the semi-transparent HTM free cells with different average transparencies from left to right,19%, 28%, 38%, 64% and 67%.
(D) The current-voltage curves of the semi-transparent HTM free cells with different average transparencies. The PCEs of the cells are 0.41%, 1.02% and 2.39% for the cells of 39%, 25% and 12% transparency, respectively.
Avoiding the use of a hole conductor has an advantage for transparency since hole transport materials absorb in the visible range resulting in decreased transparency.
All layers of the cell are deposited in an ambient environment using simple, low cost self-assembly or spin coating deposition methods (followed by different annealing processes).
The semi-transparent cells demonstrate 20%–70% transparency.
Solar cell efficiencies of devices using perovskite absorber materials have increased from 3.8% in 2009  to a certified 20.1% in 2014, making this the fastest-advancing solar technology to date. Their high efficiencies and cheap production costs make perovskite solar cells an extremely commercially attractive option, with start-up companies already promising modules on the market by 2017. 
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2. Oxford Photovoltaics oxfordpv.com Oxford PV reveals breakthrough in efficiency of new class of solar cell, 10 June 2013
3. "The Wall Street Journal: Perovskite Offers Shot at Cheaper Solar Energy" (September 28, 2014)".