We are often asked why we use monocrystalline cells instead of some of the newer technologies including amorphous silicon, CIGS and dye-based photovoltaics. The primary answer is that we’re interested in power density. We want to produce the most Watts per inch.
Since we’re making consumer electronics, the customer demand is frequently to make things with more power in less space. We’ve made a mockup of the amount of area devoted to cells if we used other cell types and still wanted to put out 4 Watts (the amount needed to charge a smartphone in a bit over 4 hours). CIGS at 12% efficiency would certainly work from a space perspective and you could probably manage amorphous at 8%. Dye-based photovoltaics at 6% spills over the backpack.
Ok, but what if you wanted to put 10 Watts on the backpack and charge an efficient laptop or tablet? Then, monocrystalline is the only one that will work unless you start making people unfold panels.
There are a couple of other reasons why we like monocrystalline cells on our solar chargers:
1. They’re super tough. Our customers really like to beat up our bags. With the flexible panels, creasing can often decrease the power output. if you’re like us and sometimes jam a backpack full of stuff or put it under a seat on an airplane, you’re going to crease the panel.
2. They degrade very slowly. The dye-based photovoltaics like those from Konarka degrade in as little as three years. Do you just tell your customer to throw away their charger? We’ve had panels outside for several years and haven’t seen any measurable drop in output.

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