Easy processing carbon paper electrode for highly efficient perovskite solar cells
Cristina Teixeira a, Luísa Andrade a, Adélio Mendes a
a LEPABE - University of Porto, Portugal, Rua Dr. Roberto Frias s/n, Porto, Portugal
Proceedings of Online International Conference on Hybrid and Organic Photovoltaics (OnlineHOPV20)
Online, Spain, 2020 May 26th - 29th
Organizers: Tracey Clarke, James Durrant, Annamaria Petrozza and Trystan Watson
Poster, Cristina Teixeira, 139
Publication date: 22nd May 2020

In this work, a thorough study was done into three different carbon papers (CP1, CP2 and CP3) for identifying the ideal features for their application as BC in a PSC. Carbon papers (CP) consists in carbon fibers matrix coated with a microporous layer made of an amorphous mixture of carbon black, graphite, and polytetrafluoroethylene (PTFE). The contact between any CP and the hole-extraction layer (HEL) demonstrated to be near ohmic (electrical energy levels of each material are correctly aligned and close enough from each other), resulting in no open-circuit voltage loss comparing with gold BC behavior. Sheet resistance of CP1 and CP2 are close to the gold BC’s one, which confirms that the CPs’ bulk is not compromising the electric charge flow. Topography is also important since higher roughness may create insulating voids that force electrical charges to transport through longer distance in HEL, which increases the charge transport resistance. By AFM and profilometry it was proved that CP2 had the better physical contact, followed by CP1. CP2 lower thickness also makes it the most malleable and flexible, allowing it to adjust its surface to the surface it is being pressured against. However, the best performing CP was CP1, which is the CP with lower load of the hydrophobic and insulator binder - PTFE. 

By simply pressing the CP against the device’s HEL, a maximum PCE of 12.93 % was achieved, which corresponds to 89 % of the PCE obtained with the typical gold BC. Besides having a much simpler and cheaper application method, the proximity between the CP and noble metal electrical resistivity, together with CP’s malleability, high mechanical resistivity, great chemical stability and low cost make this material an excellent option for flexible and large-scale photovoltaic applications. Furthermore, the PCE and relative PCE were further improved to 13.87 % and 92 % through interfacial contact optimization - depositing a thin gold layer between the HEL and CP. We deduced that a PCE over 19 % would be conceivable if standard cells reach a PCE of 20 %. 

Cristina Teixeira acknowledges project SolarPerovskite - NORTE-01-0145-FEDER-028966 funded by FEDER funds through NORTE 2020 - Programa Operacional Regional do NORTE – and by national funds (PIDDAC) through FCT/MCTES for funding; L. Andrade acknowledges FCT for funding (IF/01331/2015). The authors also acknowledge European Union's Horizon 2020 Programme, through a FET Open research and innovation action under grant agreement No 687008 (GOTSolar project). This work was also partially supported by Project WinPSC (POCI-01-0247-FEDER-017796) co-funded by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), under PORTUGAL 2020 Partnership Agreement; POCI-01-0145-FEDER-006939 (LEPABE - UID/00511/2020 ), funded by the ERDF, through COMPETE 2020  and by nationals funds through FCT; and NORTE-01-0145-FEDER-000005 – LEPABE-2-ECO-INNOVATION, supported by North Portugal Regional Operational Programme (Norte 2020), under the Portugal2020 Partnership Agreement, through the ERDF. The authors are also very thankful to CEMUP for AFM, profilometry, XPS and SEM analysis.

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