Which photovoltaic materials have direct bandgaps?

The II–VI, I–III–VI, kesterite and perovskite photovoltaic materials, such as CdTe, Cu (In,Ga)Se 2, Cu 2 ZnSn (S,Se) 4 and methylammonium lead triiodide (MAPbI 3), respectively, have direct bandgaps that enable light to be absorbed and converted into electricity in semiconductor layers that are just several micrometres thick 1, 2, 3.

Are thin film poly-crystalline CdTe solar cells able to achieve high acceptor concentrations?

Kartopu, G. et al. Study of thin film poly-crystalline CdTe solar cells presenting high acceptor concentrations achieved by in-situ arsenic doping. Sol. Energy Mater. Sol. Cells 194, 259–267 (2019).

Can a single-crystal solar cell have a bandgap similar to cdsete?

Device models and epitaxial single-crystal GaAs solar cells with a bandgap similar to CdSeTe (1.4 eV) demonstrate that Voc greater than 1.1 V, FF exceeding 85% and efficiencies of 25–28% are possible if the hole density can be increased by orders of magnitude without limiting the lifetime or photocurrent 15, 16, 17, 18.

How does substitutional doping work in polycrystalline VTD deposited films?

By enabling substitutional As doping in polycrystalline VTD deposited films, the hole density in thin polycrystalline CdTe films is increased by two to three orders of magnitude to 1 × 10 16 –1 × 10 17 without compromising carrier lifetime and is coupled with high photocurrent exceeding 30 mA cm −2.