Display substrate, display panel, display apparatus, and method of fabricating a display substrate thereof

1. A display substrate having an array of a plurality of subpixels, comprising:

a base substrate;

a pixel driving layer comprising a plurality of thin film transistors on the base substrate;

a tuning layer on a side of the pixel driving layer away from the base substrate, thicknesses of the tuning layer being different in subpixels of different colors;

a plurality of organic light emitting diodes on a side of the tuning layer away from the pixel driving layer; and

a pixel definition layer on a side of the tuning layer away from the base substrate, and defining a plurality of subpixel apertures;

wherein a respective one of the plurality of organic light emitting diodes comprises a hole injection layer, thicknesses of the hole injection layer being different in subpixels of different colors;

the thicknesses of the tuning layer and the thicknesses of the hole injection layer are negatively correlated among the subpixels of different colors;

a surface of the pixel definition layer away from the base substrate has a substantially same height relative to a main surface of the base substrate throughout the plurality of subpixels;

heights of the pixel definition layer relative to a surface of the tuning layer away from the base substrate are different in the subpixels of different colors; and

the thicknesses of the tuning layer and the heights of the pixel definition layer relative to the surface of the tuning layer are negatively correlated among the subpixels of different colors.

2. The display substrate of claim 1 , wherein the respective one of the plurality of organic light emitting diodes further comprises a first electrode between the tuning layer and the hole injection layer;

the first electrode is electrically connected to a respective one of the plurality of thin film transistors through a via extending through the tuning layer.

3. The display substrate of claim 2 , wherein heights of the first electrode relative to the base substrate being different in the subpixels of different colors;

and the heights of the first electrode relative to the base substrate and the thicknesses of the hole injection layer are negatively correlated among the subpixels of different colors.

4. The display substrate of claim 2 , wherein the respective one of the plurality of organic light emitting diodes further comprises a second electrode on a side of the hole injection layer away from the first electrode;

a microcavity in the respective one of the plurality of organic light emitting diodes is formed using the first electrode and the second electrode as reflective mirrors; and

lengths of the microcavity and the thicknesses of the tuning layer are negatively correlated among the subpixels of different colors.

5. The display substrate of claim 1 , wherein a surface of the tuning layer in a respective one of the plurality of subpixel apertures is substantially flat.

6. The display substrate of claim 1 , wherein a surface of the tuning layer in a respective one of the plurality of subpixel apertures is a stepped surface having one or a combination of one or more protrusions and one or more recesses.

7. The display substrate of claim 1 , wherein the subpixels of different colors comprise a red subpixel, a green subpixel, a blue subpixel, and a white subpixel;

a thickness of the tuning layer in the red subpixel is greater than a thickness of the tuning layer in the white subpixel;

a thickness of the tuning layer in the white subpixel is greater than a thickness of the tuning layer in the blue subpixel;

a thickness of the tuning layer in the blue subpixel is greater than a thickness of the tuning layer in the green subpixel;

a thickness of the hole injection layer in the red subpixel is less than a thickness of the hole injection layer in the white subpixel;

a thickness of the hole injection layer in the white subpixel is less than a thickness of the hole injection layer in the blue subpixel; and

a thickness of the hole injection layer in the blue subpixel is less than a thickness of the hole injection layer in the green subpixel.

8. A display apparatus, comprising the display substrate of claim 1 , and one or more integrated circuits connected to the display substrate.

9. A method of fabricating a display substrate having an array of a plurality of subpixels, comprising:

forming a pixel driving layer comprising a plurality of thin film transistors on a base substrate;

forming a tuning layer on a side of the pixel driving layer away from the base substrate, thicknesses of the tuning layer being formed differently in subpixels of different colors;

forming a plurality of organic light emitting diodes on a side of the tuning layer away from the pixel driving layer; and

forming a pixel definition layer on a side of the tuning layer away from the base substrate, to define a plurality of subpixel apertures;

wherein forming a respective one of the plurality of organic light emitting diodes comprises forming a hole injection layer, thicknesses of the hole injection layer being formed differently in subpixels of different colors;

the thicknesses of the tuning layer and the thicknesses of the hole injection layer are negatively correlated among the subpixels of different colors

a surface of the pixel definition layer away from the base substrate is formed to have a substantially same height relative to a main surface of the base substrate throughout the plurality of subpixels;

heights of the pixel definition layer relative to a surface of the tuning layer away from the base substrate are formed differently in the subpixels of different colors; and

the thicknesses of the tuning layer and the heights of the pixel definition layer relative to the surface of the tuning layer are negatively correlated among the subpixels of different colors.

10. The method of claim 9 , wherein the tuning layer having different thicknesses in the subpixels of different colors is formed in a same patterning process using a multi-tone mask plate.

11. The method of claim 10 , wherein forming a tuning layer comprises:

coating a tuning material layer on side of the pixel driving layer away from the base substrate;

exposing the tuning material layer using the multi-tone mask plate;

developing the tuning material layer subsequent to exposing the tuning material layer, thereby forming the tuning layer having different thicknesses in the subpixels of different colors.

12. The method of claim 9 , wherein the tuning layer is formed so that a surface of the tuning layer in a respective one of a plurality of subpixel apertures is substantially flat.

13. The method of claim 9 , wherein the tuning layer is formed so that a surface of the tuning layer in a respective one of a plurality of subpixel apertures is a stepped surface having one or a combination of one or more protrusions and one or more recesses.

14. The method of claim 9 , wherein forming the hole injection layer comprises:

coating a hole injection material solution to fill the plurality of subpixel apertures; and

drying the hole injection material solution, thereby forming the hole injection layer having different thicknesses in subpixels of different colors.

15. The method of claim 9 , wherein forming the hole injection layer comprises:

vapor depositing a hole injection material layer to fill the plurality of subpixel apertures; and

planarizing a surface of the hole injection material layer by polishing or thermal reflux, thereby forming the hole injection layer having different thicknesses in subpixels of different colors.

16. The method of claim 9 , wherein forming the respective one of the plurality of organic light emitting diodes further comprises forming a first electrode, the first electrode formed between the tuning layer and the hole injection layer and electrically connected to a respective one of the plurality of thin film transistors through a via extending through the tuning layer;

heights of the first electrode relative to the base substrate are formed differently in the subpixels of different colors; and

the heights of the first electrode relative to the base substrate and the thicknesses of the hole injection layer are negatively correlated among the subpixels of different colors.

17. The method of claim 16 , wherein forming the respective one of the plurality of organic light emitting diodes further comprises forming a second electrode on a side of the hole injection layer away from the first electrode, thereby forming a microcavity in the respective one of the plurality of organic light emitting diodes using the first electrode and the second electrode as reflective mirrors; and

lengths of the microcavity and the thicknesses of the tuning layer are negatively correlated among the subpixels of different colors.