Application of flexible OPVs for building integration applications Dr Jeff Kettle School of Electronics, Bangor University

Production process - Low temperature processing - Low factory investments - No shortage of raw materials - Therefore low energy payback time (1-10 day for OPV!) Lightweight and flexible→ aesthetics Lab efficiency ≈13%, module efficiency >7% in foils -Poor lifetime (18 months outdoors, T 50% ) Introduction to OPVs

OPVs for BIPV Array of demonstrators around the world (<50)…. - Si; main drawback for BIPV is price (60% more expensive) - Longer installation time - lifetime years Source: Heliatek, Dresden OPV E-Bike charger from InfinityPV ̴£800 Most OPVs laminated to building material, very few examples of direct integration

Solution processible epoxy deposition of IL layer -Steel substrates (0.3mm) have high roughness (R A = 0.25 μm, R max = 1μm) -Costs of uncoated steel is cheaper than PEN, more expensive than PET -OPV active layer is nm thick. Direct usage likely to lead to shorts -In addition, need to electrically isolate substrate from PV module -Roughness can be reduced to an acceptable value by application of solution processible epoxy layer Applying OPVs/PSCs directly to steel; challenge 1 - reducing the surface roughness

Solution processible epoxy deposition of IL layer - Steel substrates have high roughness (R A = 0.25 μm, R max = 1 μm) -OPV active layer is nm thick. Direct usage likely to lead to shorts -In addition, need to electrically isolate substrate from PV module -Roughness can be reduced to an acceptable value by application of solution processible epoxy layer -Bar coating/screen printing (with WCPC) possible to achieve R A =6m (for 0.5x0.5cm)

Key problem with OPVs on steel is finding a top electrode (no high temperatures, plasmas, compatibility of solvents etc) and low cost Challenge 2: Top electrode optimisation for OPVs on steel Variation of R SH and transparency at 550nm for a variety of top electrodes Best performance 8Ω/sq with 92% transmittance

OPV on Opaque Substrate Device Area 1cm 2

Champion Device Device Area 1cm 2 Conventional (glass) device, PCE =2.9% Conventional (PET) device, PCE=2.2%

Improvement in device performance through ‘3D’ device architectures → Capture more light at low incidence → Improve efficiency due to lower footprint AB CD Apply OPV modules to cheap corrugated substrates - Cost of substrate is £10/m 2 Applying OPVs modules building substrates

Performance under 1 sun direct irradiation Before lamination After lamination PCE (%) J SC (mA/cm 2 PCE(%) J SC (mA/cm 2 PCE gain (%) J SC gain (%) A %5.95% B %13.25% C %-40.80% D %-14.45% B is our best performing device and seems to possess the most uniform LBIC data

Yaw Pitch Pitch is the angle of the “sun” away from normal incidence and simulates the vertical tilt of the panel. (0° == panel directly pointing at the sun) Yaw is the angle of the “sun” in the horizontal plane and simulates the diurnal passage of the sun. (90° == panel directly pointing at the sun). Indoor testing of solar irradiation Efficiency of a flat module

Indoor testing of a 3D module Efficiency Relative Efficiency (to flat sample)

Outdoor performance of OPV Measurements undertaken at Bangor School of Electronics 8-cell module 3-cell module from BU  Outdoor test rig established with weather station measuring climatic conditions  Modules sourced from DTUand made internally  Benchmarking conducted with panels from Pure Wafer, Swansea, CIS from Siemens, DSCs 3-D OPV modules

Outdoor performance in Bangor– Summer 2015 Sunny Cloudy

Outdoor performance in Bangor– June-August, 2015 Flat Corrugated module Average Daily yield (mWh/cm 2 ) Sunny (+17%) Intermediate (+21%) Diffuse (+29%) Average yield at peak periods ( pm) [mWh/cm 2 ] Sunny (+55%) Intermediate (+57%) Diffuse (+60%) Kettle, Jeff, et al. Energy & Environmental Science 8.11 (2015):

Conclusions OPVs made directly on ‘cheap and rough’ steel substrates by applying a low cost planarization layer. The technique can be employed on different building material e.g slate, concrete Silver nanowire electrode deposited directly onto OPV yields impressive material properties R SH =15Ω/sq at transmittance of 92% Corrugated BIPV products can yield advantages over flat modules – improved PCE, performance in diffuse conditions, and in early morning/evening

Acknowledgements - Noel Bristow, Dr Huw Waters, Dr Ziqian Ding, Vasil Stoichkov, Helder Anzelli, Ricardo Fernandes, Dr Sanjay Ghosh - Prof F Krebs group, DTU - Dr Tracy Sweet, Cardiff University -Dr Pascal Sanchez, Dr David Gomez, Dr MF Fernandez, Fundacion ITMA -Dr Tatyana Korochkina, Prof Gethin, WCPC

Save the date; PVSAT-13, April 5 th -7 th, 2017 Bangor University, Wales