Control of valence band offset of Cu(In,Ga)Se₂solar cells with single-graded band profile

Abstract

We have revealed that the insertion of a Cu(In,Ga)3Se5 layer at the CdS/Cu(In,Ga)Se2 interface is effective for improving the efficiency of Cu(In,Ga)Se2 solar cells fabricated at low temperatures and with single-graded band profiles. Although the double-graded profile is usually adopted for Cu(In,Ga)Se2 solar cells grown at around 600 °C, the single-graded profile is more suitable for low-temperature-grown solar cells owing to the higher controllability of band profiling. We also analyzed the role of the Cu(In,Ga)3Se5 layer by transmission electron microscopy energy-dispersive X-ray spectrometry (TEM–EDX) and scanning electron microscopy electron-beam-induced current (SEM-EBIC), and found that Cd diffuses to the Cu(In,Ga)3Se5 layer, resulting in a shift of the pn-junction electrical interface from the highly defective structural interface. Finally, by applying this new band profile, VOC and FF increased, resulting in an efficiency improvement from 13.4 to 14.5% at a substrate temperature of 450 °C.

Benefits of Low Electron-Affinity Material as the N-Type Layer for Cu(In,Ga)S2 Solar Cell

“…The additional step of absorber layer's post-deposition treatment (PDT) using alkali [16,17] have also been known to have a positive impact on the CIGSe 2 solar cell's performance. In addition, the importance of the pn-junction interface between the buffer layer and the absorber layer in non-radiative recombination was identified empirically [18][19][20] and further validated through a numerical study [21]. The abundance of work on the narrow band gap CIGSe 2 solar cells established the current efficiency record of 23.35% [22] for a single-junction narrow-band gap CIG(SSe) 2 solar cell with E g = 1.09 eV.…”

Controllable Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2 Solar Cells

“…Meanwhile, the smaller E u confirmed the larger V OC in the device with OVC phase. [13,15,17] To elucidate underlying reasons for efficiency improvement for CIGS with OVC phase, we firstly examined the temperature dependent J-V evolutions in the dark condition for CIGS with/ without OVC phase (Figure 5a,b). For CIGS device without OVC, the diode-like behavior was largely suppressed when the temperature was lower than 250 K. [3] By contrast, for CIGS device with OVC, the J-V curves show good diode characteristics until the temperature decreased to 120 K. This demonstrated the lower transmission barrier in the CIGS device with OVC.…”

“…Tremendous research efforts have been implemented to study the formation of OVC phase in vacuum based process. [ 15–17 ] Nevertheless, limited studies are investigating the OVC formation through solution process. Current studies have reported the existence of OVC phase in high efficiencies solution processed CIGS solar cells, confirming the indispensability of OVC phase.…”

Silver‐Doped Cu2(Sn,Ge)S3 Solar Cells

“…[3][4][5][6][7] By mutual diffusion of Ga and In elements, conduction band gradient in CIGSe or CIGSSe was controlled, enhancing the minority carrier collection efficiency owing to an electric field. [8][9][10][11][12] In the CIGSSe solar cells, by incorporating S element into CIGSSe surface during the sulfurization process, interfacial recombination was reduced by the carrier separation near the heterojunction due to a bandgap widening. [13][14][15][16] Control of wide-bandgap Cu-deficient phases such as Cu 2 (In,Ga) 4 Se 7 , Cu(In,Ga) 3 Se 5 , and Cu(In,Ga) 5 Se 8 near the CIGSe surface has been developed.…”